PREVALENCE OF OXYTETRACYCLINE RESIDUE AND RESISTANT 
ESCHERICHIA COLI O157:H7 IN BEEF AND CHICKEN IN SELECTED CITIES OF 
SOUTH WESTERN NIGERIA 
 
BY 
 
OLATOYE ISAAC OLUFEMI, 
DVM, MVPH (Ibadan) 
 
A thesis in the Department of Veterinary Public Health and Preventive Medicine 
Submitted to the Faculty of Veterinary Medicine in partial fulfilment of the requirements for 
the degree of 
DOCTOR OF PHILOSOPHY (PhD) 
of the 
UNIVERSITY OF IBADAN 
 
 
August 2011 
 
ABSTRACT 
The use of antibiotics in livestock production is of food safety concern due to hazards of their 
residues and transfer of resistant bacteria along the food chain. There are few reported 
quantitative assessment of meat-borne antibiotic residues and resistant pathogens in 
southwestern Nigeria. Antibiotics usage in food animal production, antimicrobial residues 
screening, prevalence of Escherichia coli O157:H7 and levels of oxytetracycline residue in 
chicken and beef from Lagos, Ibadan and Akure were investigated.  
A semi-structured questionnaire was administered to 30 poultry and 20 cattle producers 
purposively selected from the study areas to obtain data on types and sources of antibiotics 
used, knowledge of disease recognition and practice of withdrawal periods in food animals. 
Two hundred and fifty samples each of kidney, liver and muscles of slaughtered cattle from 
one abattoir and 200 samples each of breast muscle and liver from chicken markets and 
broiler farms in each study area were collected between January 2006 and December 2009. 
The samples were screened for antimicrobial residues using rapid microbial inhibition assay. 
Oxytetracycline residue levels were determined by high performance liquid chromatography. 
Escherichia coli O157:H7 was isolated and screened by culture and latex agglutination 
respectively. Antibiotics susceptibility of the isolates was performed using multi-disc 
diffusion method. Data were analysed using descriptive statistics and ANOVA at p<0.05. The 
residue levels were compared with Codex Alimentarius Maximum Residue Limits (MRLs) 
and residue prevalence in beef during the wet and dry seasons were also compared.  
All the respondents administered antibiotics without veterinary prescription, with 
oxytetracycline being the most commonly used. Most (95.0%) of the producers never 
observed withdrawal periods and 75% of them did not know the importance of withdrawal 
i 
periods and hazards of antibiotic residues. Antibiotic residues prevalence in beef was 48.5%, 
44.5% and 44.5% in Ibadan, Lagos and Akure respectively. In chicken, prevalence of 76.0% 
and 69.5% were obtained in Ibadan markets and farms compared to 70.0% and 61.0% in 
Lagos markets and farms respectively. Mean oxytetracycline residue concentrations of 
1324.7±148.0, 856.6±118.0 and 651.7±101.3µg/kg were obtained in bovine kidney, liver and 
beef respectively with 37.8, 40.3 and 47.5% of these samples containing residues above 
MRLs. The levels in chicken liver and muscle were 1042.0±122.8 and 615.0±91.8µg/kg 
respectively of which 50.7% and 58.8% contained residues above MRLs. The prevalence of 
antimicrobial residue was significantly higher in chicken than in beef and during wet than dry 
season in beef. The prevalence of E. coli O157:H7 in beef from Ibadan and Lagos were 
28.5% and 11.0%, while those of chicken from Ibadan and Lagos markets were 13.0% and 
14.0%, and from Ibadan and Lagos farms were 18.0% and 13.0% respectively. All the 
isolates were resistant to one or multiple antibiotics, but the highest resistance of 91.1% was 
to tetracycline. 
Indiscriminate antibiotics usage predisposes meat consumers to risks of antibiotic residues 
and resistant Escherichia coli O157:H7 in southwestern Nigeria. Regulatory control of 
antibiotics usage in livestock production, meat inspection and pharmaco-epidemiological 
surveillance of food animals is hereby recommended to ensure safe meat supply. 
Key words: Antibiotic usage, Chicken, Beef, Oxytetracycline residue, Escherichia coli 
O157:H7  
Word Count:  496. 
 
ii 
DEDICATION 
The work is dedicated to the Almighty God for the beautiful world he gives us and the power 
to dominate the creations including food animals to live well. To HIM be all the glory.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
iii 
 
CERTIFICATION 
 
This is to certify that this work was carried out by 
ISAAC OLUFEMI OLATOYE 
 
AT 
THE DEPARTMENT OF VETERINARY PUBLIC HEALTH AND PREVENTIVE 
MEDICINE, 
UNIVERSITY OF IBADAN 
 
UNDER THE SUPERVISION OF 
 
 
.................................................................. 
Professor G. A. T. Ogundipe 
DVM, MVPM, Ph.D (Ibadan); FCVSN 
 
 
iv 
Acknowledgement 
To GOD be the GLORY. 
My most sincere thanks go to my supervisor Prof. G.A.T. Ogundipe, for his guidance, 
support and encouragement throughout the whole process of this research work. 
This study was carried out at the Department of Veterinary Public Health and Preventive 
Medicine, Faculty of Veterinary Medicine, University of Ibadan, Ibadan. The support of this 
research by IDRC/ILRI and the Postgraduate School of University of Ibadan are gratefully 
acknowledged. I appreciate everyone who has supported me professionally and technically. I 
thank the past and present Heads of the Department of Veterinary Public Health and 
Preventive Medicine. I am particularly indebted to my colleagues; Engr (Dr) Adewole, Drs. 
Debo Saba, Babasola Olugasa, Elizabeth Amosun, Olanike Adeyemo, Kunle Ayinmode, 
Dimeji Oluwayelu, Debo Olukole, Segun Oriade, Yinka Oridupa, Emma Awosanya, and 
Sanmi Aina for their immense contributions at various stages of this work. 
 Dr. I. F. Ijagbone, the Director General of Nigerian Institute of Science Laboratory 
Technology (NISLT) is highly appreciated for the immeasurable assistance and the access to 
use the HPLC machine and other equipment in the Chemical Analytical Laboratory of 
NISLT. Dr. Yetunde Kolade, Messrs. Ipinmoye, Ishola and Ajayi are especially thanked for 
teaching me skilfully the principles and operations of liquid chromatography. I am also 
grateful to Messers Ojomo, Okunlade and Mrs. Kolawole for their technical assistance in 
laboratory works throughout these years.  
 
 
v 
To the entire staff of the Department of VPHPM, it has been my pleasure to work together for 
the pursuance of one health goal. I thank you all for your various contributions to this work. 
Many colleagues offered their support and assistance whenever needed. The contributions of 
Professors D. R. Call, G. Palmer, Lisa Orfe and all the members of Call Laboratory of 
Molecular Epidemiology, Pathogenomic and Proteiomic team at Washington State University 
and their constructive and valuable criticisms are highly appreciated. I also say a big thanks 
to Vaughn Sweet and Njansi Uchendu of WSU for their love and prayers.  
I am grateful to the my colleagues and friends in veterinary drugs marketing; Drs Olatunde 
Agbato (Animal Care Ltd), Ibrahim Adekunle (Global Vet Konsult), S.O. Adeyemi (Soptimal 
Ventures), Ogunbeku Biodun, Eegunyika Aderemi, Olaofe Olaitan (Chi Ltd), and the 
livestock farmers for our field romance and assistance in data collection. Our aggression to 
sell veterinary drugs prodded my quest to the fascinating world of antibiotic residues and 
resistance science. The veterinary inspectors and butchers deserve profound thanks for their 
cooperation in samples collection at the abattoirs and slaughterhouses.  
My profound gratitude also goes to my angel mother (Chief Julie Olatoye) my brother (Mr. 
Kayode Olatoye) and my sisters who believe in my God giving potentials for academic 
excellence/ thank you for your love, support and encouragement. 
Finally, my deepest appreciation and gratitude go to „My Sweet Heart‟ Yemisi Temilola who 
has been so patient and had so much faith in me and also in many practical ways has helped 
to carry this work to completion God bless you darling. Thanks to our lovely children Joy-
Bolu, Faith-Shalom, Righteous-Daniel, Blessed-Israel and Queen-Esther for bringing so 
much joy into our lives and for all the good times we have had so far, and for helping me 
keep things in healthy proportion. It is your turn to shine. Greater heights shall you reach.  
vi 
TABLE OF CONTENTS 
Abstract ………………………………………………………………………………………..i 
Dedication ................................................................................................................................iii 
Certification ..............................................................................................................................iv 
Acknowledgement .....................................................................................................................v 
Table of contents .....................................................................................................................vii 
List of appendices ....................................................................................................................xv 
List of tables ...........................................................................................................................xvi 
List of figures ........................................................................................................................xvii 
List of abbreviations...............................................................................................................xvii 
CHAPTER ONE: GENERAL INTRODUCTION...............................................................1 
1.1 Background Information ...............................................................................................1 
1.2 Research Questions .......................................................................................................4 
1.3 Objectives ......................................................................................................................5 
1.4 Justifications ..................................................................................................................5 
1.5 Study Hypotheses...........................................................................................................6 
1.6 Description of study Area..............................................................................................7 
1.6 Limitations of study.......................................................................................................8 
vii 
CHAPTER TWO: LITERATURE REVIEW.....................................................................10 
2.1.1 Food Animal Production in Nigeria.............................................................................10 
2.1.2 Changing patterns of livestock production and consumption......................................13 
 2.1.3 World Food Situation and Safety Concerns.................................................................19 
 2.2 Antibiotics....................................................................................................................20 
 2.2.1 Historical Overview of Antibiotics..............................................................................20 
2.2.2 Classification of Antibiotics.........................................................................................22 
2.2.3 Mode of action of Antibiotics......................................................................................23 
2.2.4 Metabolism of antibiotics.............................................................................................26 
2.2.5 Antibiotic Resistance………………….……………………………………………...27 
2.2.5.1 Resistance Mechanisms, Cross-Resistance and Co-Selection.....................................28 
2.2.5.2 Vectors of Antibiotic Resistance…………………………………………………….33 
2.2.5.2.1 Plasmids……………………………………………………………………………33 
2.2.5.2.2 Transposons………………………………………………………………………...33 
2.2.5.2.3 Integrons……………………………………………………………………………34 
2.2.5.3 Determination of Antibiotic Resistance......................................................................35 
2.2.6 Antibiotics Drug Residues in Food Animals...............................................................38 
2.2.6.1 Tetracyclines Residue.................................................................................................38 
viii 
2.2.6.2 Causes of antimicrobial residues in meat…………………………………………….39 
2.2.6.3 Public health risks of antimicrobial residues…………………………………………41 
2.2.6.4 Effects of residues on gut microbata............................................................................41 
2.2.6.5 Hypersensitivity reactions............................................................................................42 
2.2.6.6 Other harmful effects..................................................................................................43 
2.2.7 Safety factors for the evaluation of antimicrobial drug residues....................................44 
2.2.7.1 Acceptable daily intake (ADI) ...................................................................................45 
2.2.7.2 Maximum Residue Limit (MRL) ................................................................................46 
2.2.7.3 Withdrawal period......................................................................................................47 
2.2.8 Detection and Analysis of Antibiotics Residues..........................................................48 
2.2.8.1 Detection and Identification of Antimicrobial Residues..............................................49 
2.8.1 Screening Methods.......................................................................................................50 
2.2.8.1.1 Microbiological Assay ....................................................................................50 
 (i) The four-plate test (FPT) .................................................................................51 
 (ii) The swab test on premises (STOP) .................................................................51 
2.2.8.1.2 Immunological Techniques..............................................................................51 
2.2.8.1.3 Antibiotics Residues Rapid Screening Kits.....................................................52 
 (i) Charm II Test ..................................................................................................53 
ix 
 
 (ii) Premitest...........................................................................................................53 
2.8.2 Physico-chemical (Quantitative) Residue Analysis Methods......................................54 
2.8.2.1 Chromatographic Techniques......................................................................................54 
(i) Sample Preparation ....................................................................................................56 
 (a) Extraction: .............................................................................................................56 
 (b) Clean-up: ...............................................................................................................57 
(ii) Chromatographic separation........................................................................................58 
 (iii) Resolution and Detection............................................................................................58 
2.9 Antimicrobials use in Livestock ..................................................................................58 
2.9.1 Antibiotics as Growth Promoters.................................................................................60 
2.9.2 Antimicrobials Use in Animal and Resistant Bacteria Transfer to Man. ....................61 
2.9.3 Regulatory Control of Veterinary Drugs Use and Residues in Food Animals. ..........65 
2.10 FAO/WHO Residue Control and World Trade Organisation (WTO) ........................66 
2.10.1 Codex Alimentarius Commission (CAC) ....................................................................67 
2.10.2 Control of antimicrobial use and residues in different countries.................................69 
2.10.3 Veterinary Drug Use and Control in Developing Countries.......................................72 
2.10.4 Drug Usage and Antibiotic Residues in Livestock Products in Nigeria......................74  
x 
2.10.5 Nigerian Food and drug Safety Policies.....................................................................76 
CHAPTER THREE: SURVEY OF THE USAGE OF ANTIBIOTICS USAGE BY 
CATTLE AND POULTRY PRODUCERS IN SOUTHWEST NIGERIA.......................81 
3.1 Introduction..................................................................................................................81 
3.2 Materials and Methods.................................................................................................82  
3.2.1 Materials.......................................................................................................................82 
3.2.2 Methods.......................................................................................................................82 
3.2.2.1 Sampling Procedures....................................................................................................82 
3.2.2.2 Questionnaire interview...............................................................................................82 
3.2.2.3 Data Analysis...............................................................................................................83 
843.3 Results..........................................................................................................................83 
3.3.1 Livestock farmers Characteristics ...............................................................................83 
3.3.2 Flock/Herd Structure and Management Systems.........................................................84 
3.3.3 Feed and Feeding of the poultry and cattle..................................................................84 
3.3.4 Diseases Status of the Poultry and Cattle.....................................................................86 
3.3.5 The use of drugs in poultry and cattle .........................................................................89 
3.3.6 Farmers knowledge of withdrawal period and drug residues.......................................93 
3.4 Discussion........................................................................................................................96 
xi 
CHAPTER FOUR: DETECTION OF ANTIBIOTIC RESIDUES AND 
QUANTITATIVE ANALYSIS OF OXYTETRACYCLINE RESIDUES IN CATTLE 
AND CHICKEN MEAT IN SOUTHWEST NIGERIA......................................................97 
4.1 Introduction..................................................................................................................97 
4.2 Materials and Methods...............................................................................................100 
4.2.1 Samples collection......................................................................................................100 
4.2.2 Screening of Beef and Chicken for Antimicrobial Residues.....................................103 
4.2.3 Chromatographic Analysis of Oxytetracycline Residue in beef and Chicken...........104 
4.2.3.1 HPLC Chromatographic conditions………………………………………………..104 
4.2.3.2 Sample Preparation....................................................................................................104 
4.2.2.3 Preparation of Standard Curve..................................................................................105 
4.2.2.4 Procedure for HPLC analysis of oxytetracycline......................................................105 
4.2.2.5 Recovery Experiment.................................................................................................106 
4.3 Results..............................................................................................................................107 
4.3.1 Prevalence of antimicrobial residues in beef..............................................................107 
4.3.2 Prevalence of antimicrobial residues in chicken........................................................110 
4.3.3 Results of oxytetracycline residue................................................................................113 
4.3.3.1 Calibration Curve and Recovery Experiment............................................................113 
xii 
4.3.3.2 Prevalence of oxytetracycline residue in beef............................................................118 
4.3.3.3 Prevalence of xytetracycline residue in beef from Ibadan (Bodija) abattoir..............121 
4.3.3.4 Prevalence of oxytetracycline residue in beef from Akure (Araromi) abattoir..........123 
4.3.3.5 Prevalence of oxytetracyline residue in beef from Lagos (Oko-Oba) abattoir..........125 
4.3.3.6 Prevalence of oxytetracycline residue in chicken samples from farms and markets in
 Lagos and Ibadan.......................................................................................................127 
4.3.4 Hypotheses testing......................................................................................................132 
4.4 Discussion..................................................................................................................133 
CHAPTER FIVE: ISOLATION AND ANTIBIOTICS SUSCEPTIBILITY OF 
ESCHERICHIA COLI O157:H7 FROM BEEF AND CHICKEN IN IBADAN AND 
LAGOS..................................................................................................................................138 
5.1 Introduction................................................................................................................138 
5.2 Materials and Methods.....................................................................................................141 
5.2.1 Sterilization of Glass Wares and Preparation of Culture Media................................141 
5.2.2 Preparation of microbiological media for bacterial isolation and identification........141 
5.2.3 Samples and Sampling Procedures............................................................................142 
5.2.4 Bacterial isolation......................................................................................................142 
5.2.5 Identification and Biochemical Tests........................................................................143 
xiii 
5.2.6 Determination of Antibiotic Susceptibility and resistance pattern of E. coli O157
 isolates............................................................................................................146 
5.2.7 Statistical Analysis.....................................................................................................147 
5.3 Results........................................................................................................................147 
6.3.1 Prevalence of E. coli O157:H7 in Beef and Chicken.................................................147 
6.3.2  Antibiotics susceptibility and resistance pattern of E. coli O157 isolates..................149 
6.4 Discussion..................................................................................................................153 
CHAPTER SIX  CONLUSIONS AND RECOMMENDATIONS...........................157 
6.1 Conclusions................................................................................................................157 
6.2 Contributions to Knowledge......................................................................................158  
6.3 Recommendations......................................................................................................160 
References..................................................................................................................163 
Appendixes................................................................................................................206 
 
 
 
 
 
xiv 
 
LIST OF APPENDIXES 
Appendix                    Page 
Appendix i: Codex Definitions on antibiotics and residue.....................................................206 
Appendix iia: Questionnaire on antibiotics usage in cattle in Nigeria……………………...211 
Appendix iib: Questionnaire on antibiotics usage in poultry in nigeria…………………….215 
Appendix iiia: List of Respondent Poultry Farmers………………………………………...218 
Appendix iiib: List of Respondent Cattle Producers………………………………………..220 
Appendix iv: Codex Alimentarius Commission Maximum Residue Limits for  
Tetracylines in Foods……………………………………………………….222 
Appendix v: Table of Number of samples required to detect at least one non-compliant 
  result with pre-defined probabilities in a population having known non- 
  compliance residue prevalence. …………………………………………….224 
Appendix vi: Preparation of reagents and buffers…………………………………………..225 
Appendix vii: Statistical Tables OTC residue in beef and chicken……………………………..227 
 
 
 
xv 
LIST OF TABLES 
Table                     Page 
2.1 Livestock population in West Africa............................................................................12 
2.2 Production of Cattle Meat...........................................................................................17 
2.3 Production of Chicken Meat.......................................................................................18 
2.4 Molecular typing antibiotic resistance methods...........................................................36 
3.1 Farmers characteristics and flock/herd structure.........................................................87 
3.2 Indications for the use of Antimicrobials in Poultry and cattle....................................89 
3.3 Compliance with Withdrawal Period among the Poultry and cattle farmers...............92 
4.1a Distribution of beef samples...........................................................................................101 
4.1b Distribution of chicken samples.....................................................................................101 
R
4.2 Premi Test Screening of beef for antimicrobial residues................................................108 
4.3 Prevalence of antimicrobial residues in chicken from Ibadan and Lagos........................111 
4.4 Recovery of oxytetracycline from spiked tissues.............................................................117 
4.5 Seasonal Prevalence of oxytetracycline residue in beef...................................................119 
4.6 Prevalence of oxytetracycline in beef above the MRLs...................................................120 
4.7 Oxytetracycline residue in beef from Ibadan (Bodija) abattoir........................................122 
4.8 Oxytetracycline residue in beef samples from Akure (Araromi) abattoir........................124 
xvi 
4.9 Oxytetracycline residue in beef from Lagos (Oko-Oba) abattoir.....................................126 
4.10 Oxytetracycline residue in chicken from Ibadan............................................................128 
4.11 Oxytetracycline residue in chicken from Lagos.............................................................129 
5.1 Distribution of E. coli 0157 strains isolated from slaughtered cattle and  
 chicken meat...............................................................................................................148  
5.2 Frequencies of Antibiotics Resistant E. coli O157:H7 isolates from Beef................150 
5.3 Frequencies of antibiotics resistant E. coli O157:H7 isolates from chicken..............151 
5.4 Antibiotic resistance patterns of E. coli O157:H7 isolates from Beef.......................152 
5.5 Antibiotic resistance patterns of E. coli O157:H7 isolates from chicken..................153 
 
 
 
 
 
 
 
 
 
xvii 
LIST OF FIGURES 
Figure                      Page 
1.1 Map of southwest Nigeria showing the study areas.......................................................9 
2.1 Chemical Structures of Some Antibiotics....................................................................24 
2.2 Mechanisms of Action of Antibiotics..........................................................................31 
2.3 Ecology of antibiotic resistance and routes of transmission........................................64 
3.1 Commonly encountered poultry diseases reported by the respondents.......................86 
3.2  Commonly encountered cattle diseases reported by the respondents..........................87 
3.3 Commonly used antibiotics in poultry and cattle ........................................................90 
3.4 Farmers knowledge of the effects of drugs residues in egg/meat................................93 
4.1: Seasonal prevalence of antimicrobial residues in beef from abattoirs in the cities.........109 
®
4.2 Prevalence antimicrobial residues in chicken meat by Premi Test Screening................112 
4.3 Calibration curve of oxytetracycline analytical standard.................................................114 
4.4a: Chromatographs of oxytetracycline standard...........................................................................115 
4.4b: Chromatographs of oxytetracycline in meat samples....................................................116 
4.5: Mean oxytetracycline residue levels in beef and chicken from southwest Nigeria.......130 
4.6: Seasonal prevalence of oxytetracycline residue in cattle................................................131 
 
xviii 
LIST OF ABBREVIATIONS 
ADI  Acceptable Daily Intake 
CAC   Codex Alimentarius Commission 
CCFH   Codex Committee on Food Hygiene 
CCP   Critical Control Point 
CCRVDF  Codex Committee on Residues of Veterinary Drugs in Foods 
EUCVM European Union Center for Veterinary Medicine  
FAO   Food and Agriculture Organization of the United Nations 
FDA   US Food and Drug Administration 
GAP  Good Agricultural Practice 
GATT  General Agreement on Trade and Tariff 
GDP   Gross Domestic Product 
GVP  Good Veterinary Practice 
HPLC  High Performance Liquid Chromatography 
HACCP  Hazard Analysis Critical Control Point (System) 
JECFA  Joint FAO/WHO Expert Committee on Food Additives 
JMPR   Joint FAO/WHO Meetings on Pesticide Residues 
LC-MS  Liquid chromatography – mass spectrometry 
xix 
MRL   Maximum residual level 
MRL  Maximum Residue Limit 
MRLVD  Maximum residual level of veterinary drug 
NAFDAC National Agency for Food and Drug Admnistration and Control  
OIE  Office International des epizooties/International Office of Epizooties 
OTC  Oxytetracycline 
SPS   Sanitary and phytosanitary measures 
TBT  Agreement Agreement on the Technical Barriers to Trade 
WHO   World Health Organization 
WTO  World Trade Organization 
DANMAP Danish Integrated Antimicrobial Resistance Monitoring and Research 
  Programme, Denmark 
NARMS National Antimicrobial Resistance Monitoring System, USA 
JVARM Japanese Veterinary Antimicrobial Resistance Monitoring System, Japan, 
MARAN Monitoring Antimicrobial Resistance And Antibiotic Usage Animals, The 
  Netherlands  
CIPARS Canadian Integrated Program for Antimicrobial Resistance Surveillance,  
IIMAR Indian Initiative for Management of Antibiotic Resistance, 
xx 
SVARM Swedish Veterinary Antimicrobial Resistance Monitoring 
NORM-VET Usage of Antimicrobial Agents and Occurrence of Antimicrobial Resistance 
Monitoring in Norway 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
xxi 
CHAPTER ONE 
GENERAL INTRODUCTION 
1.1 Background information  
Food security comprising of food availability and safety are major global challenges of the 
st
21  century. The 1996 world food summit was concluded with declaration that “all countries 
of the world should rise up to the challenge of hunger eradication to feed the growing human 
population” (FAO, 1996). Nigerian livestock production is an integral part of agriculture 
contributing about 7% to the nation‟s Gross Domestic Product (Blench, 1999). The pressure 
of food demand in quantity and quality sought by consumers require a variety of intensive 
technologies and large scale agricultural production including livestock husbandry which 
provides animal protein in human diet. 
Drugs, vaccines and some chemicals are employed in livestock to combat the challenges of 
infectious organisms and to enhance productivity. Commercial rearing of animals for food 
depends on the use of pharmacologically active compounds (drugs) which are beneficial to 
health, well-being and economics of the livestock industry.  The five major classes of drugs 
used in food animals include: antibiotics; antiparasitic drugs; steroid anabolic growth 
promoters; ionophores; and topical antiseptics. Antibiotics are used in livestock 
prophylactically and therapeutically to combat infections by bacteria and also to improve 
productivity and as growth promoter antibiotics (GPA). Since the first discovery of penicillin 
by Alexander Fleming in 1928 (Fleming, 1929) and its subsequent clinical importance in the 
1940s, antimicrobial agents have played revolutionary role in human and animal health 
(Abraham and Chain, 1940; Abraham et al., 1941). The reported benefits of drug use in 
livestock result from the maintenance of good animal health thereby reducing the chance that 
pathogenic agents will spread to humans from animals.  
Following the administration of these drugs to food animals, residues of the parent drugs or 
their metabolites may be deposited in edible portions (meat milk and eggs) of such animals 
(Schmidt and Rodrick, 2003). The potential health hazards of drug residues in food were 
categorised into three namely toxicological, microbiological and immunological effects (Van 
Dresser and Wilke, 1989). Oxytetracycline, streptomycin, penicillin and sulphamethazine 
have been reported as the most frequently used and detected antibiotics in tissues food 
animals (Van Dresser and Wilke, 1989; Rivere and Spoon, 1995; Phillips et al., 2004; 
Posyniak et al., 2005). Concerns on public health risks of residues in animal foods began with 
the linkage identified between outbreak of resistant bacterial infections in the people that 
consumed calves and milk with antibiotic residue in U. K. in 1960. Swann committee 
subsequently recommended stringent control of the use of antibiotics in food producing 
animals to protect public health (Swann et al., 1969). 
 A major public health concern about the presence of antibiotics residues in food is their 
contribution to development, spread and transfer of antibiotic resistant bacteria and genes 
along the food chain. There is also concern about continued dissemination and spread of 
antibiotic resistance from the co-mingling of antibiotic resistant bacteria with the natural 
micro-flora in animal and human gut leading to the disruption of gastrointestinal microbial 
ecology. This could results in food-borne zoonoses caused by multi-drug resistance (MDR) 
pathogens resulting from the selective pressure exerted by the exposure to antibiotics (Alanis, 
2005; Kumai et al., 2005). 
Other reported health hazards of antibiotics residues in food chain when consumed at 
violative levels include allergic or hypersensitivity reactions, carcinogenic, mutagenic and 
toxic effects in man (Dewdney et al., 1991; Berends et al., 2001; Nisha, 2008). Economic 
loses also arise from meat, milk and eggs condemnations at national and international trade 
levels when residues are detected at violative levels. Furthermore, milk contaminated with 
even low concentrations of antimicrobial drug residues also create technological difficulties 
in the production of fermented milk products by inhibiting the growth of the starter cultures 
leading to economic loss in dairy industry (Heeschen and Blüthgen, 1991).  
Developed nations are employing strict regulatory monitoring of antibiotics use and residues 
in order to safe guard against the associated health hazards (van den Bogaard, 1998). 
However, antibiotics are also widely and indiscriminate use in developing countries but the 
quantities being used are difficult to obtain due to lack of regulatory control of their uses 
(Mitema et al., 2001; Al Mustafa and Al Ghamdi, 2002). International, national and regional 
efforts in setting residues safety standards: maximum residue limits (MRLs) and acceptable 
daily intake (ADI) for the various drugs and chemicals used in livestock production are 
ongoing and are major requirements in food exports. Global food trade with little or no tariff 
and barrier (including drug residues) is a primary objective of the General Agreement on 
Tariffs and Trade (GATT) 1994 culminating in establishment of World Trade Organization 
(WTO) on January 1, 1995 with Codex Alimentarius Commission (CAC) as the international 
standard food safety regulatory body. The Codex Alimentarius Commission is a joint 
committee of Food and Agriculture Organisation (FAO) and World Health Organisation 
(WHO) that sets and recommends food safety standards (codex) to promote international 
trade. Withdrawal periods are also established as the time required for the residue of 
toxicological concern to reach safe concentration before slaughtering of treated animals or 
harvesting milk and eggs for human consumption.  
Veterinarians and livestock producers have ethical responsibility of prudent use of drugs in 
livestock and are expected to observe the withdrawal periods prior to the slaughtering of 
animals or harvesting of milk and egg for human consumption. When drug manufacturers and 
national legislative directions are followed by livestock producers and the veterinarians, drug 
residue levels in food of animal origin are expected to be within safe limits. But where levels 
of residue exceed permitted maximum limits, they are usually caused by improper use and as 
such food should legally not be allowed into the food system. More so, carcasses of such 
animals can be carriers of food borne pathogens including E. coli that could be resistant to the 
antibiotics, thereby exposing the consumers to the associated public health risks of antibiotic 
residues and bacterial resistance. Several authors have isolated resistant foodborne pathogens 
from meat, in some part of Nigeria (Aibinu et al., 2007; Umolu, et al., 2006; Okeke et. al., 
2007).  
This study therefore was aimed at investigating the practice of drug administration in poultry 
and cattle production and quantifying residues of oxytetracycline in the chicken and beef 
meant for human consumption in selected cities of south western Nigeria. Also the 
prevalence and antibiotic resistance patterns of Escherichia coli O157:H7 isolated from the 
meat was also investigated. 
1.2 Research questions 
(i) What are the patterns of veterinary drug usage in cattle and poultry production? 
(ii) What is the prevalence of antibiotic residues in beef and chicken being consumed in
 selected cities of southwest Nigeria? 
(iii) What are the levels of oxytetracycline residues in beef and chicken meant for human
 consumption in Akure, Ibadan and Lagos? 
(iv) What is the prevalence of Escherichia coli O157:H7 contamination and its antibiotics
 resistance pattern in beef and chicken across the cities? 
 
 
1.3 Objectives 
The overall objective of this study is to determine the wholesomeness of beef and chicken 
with respect to the deposition of residue of oxytetracycline and contamination with 
Escherichia coli O157:H7 of meats from selected cities of southwest Nigeria  
The specific objectives are:  
(i) To assess the culture (i.e. knowledge, attitude and practice) of poultry and cattle 
  producers in southwest Nigeria on the administration of antibiotics to their livsetock. 
(ii) To determine the prevalence of antibiotic residues in beef and chicken in the cities of
   Ibadan, Akure and Lagos. 
(iii) To quantify the levels of oxytetracycline residues in beef and chicken from 
  Ibadan, Akure and Lagos. 
(iv) To determine the prevalence and antibiotics resistance patterns of E. coli O157:H7
  contamination of the beef and chicken samples from the cities. 
1.4 Justifications 
Beef and chicken have wide consumer acceptability and they constitute more than 60% of 
meat consumption in Nigerian cities. These meats are obtained mostly from commercial 
poultry and semi-intensive cattle production. Veterinary drugs including antibiotics are 
commonly administered to these animals indiscriminately.  
Antibiotic use in food animals is of global and public health concerns and also a critical 
regulatory function of the codex alimentarius commission for SPS regulations in World Trade 
Organisation (WTO) to which Nigeria subscribes. Compliance with such international 
standards will ensure participation in international food and meat trade. There is no 
regulatory monitoring of the use of veterinary drugs, no national antibiotics residues and 
resistance monitoring or surveillance and there are no residue limits (MRL or ADI) set for 
veterinary drugs in foods in Nigeria (Aliu, 2004). Previous studies in Nigeria have shown 
qualitative presence of antibiotics residues in meat. There is need for quantitative analysis of 
residues in theses food using more sensitive and specific detection methods such as HPLC.  
In addition, meat-borne bacteria due to contamination of the meat with fecal material or 
ingesta during the slaughtering process have been repeatedly isolated with E. coli as an 
indicator organism. These bacteria are also resistant to most commonly used antibiotics and 
can subsequently be transfer to human beings via the food chain. E. coli O157:H7 is one of 
the emerging food-borne pathogens that have been isolated from beef and chicken 
worldwide. Consequent to the practices of floor slaughtering and meat processing in most 
abattoirs in Nigeria there is the need to investigate the prevalence of meat contamination with 
such zoonotic pathogens and its antibiotics resistance patterns. 
The results from this study would supply the hitherto unavailable baseline information on the 
quantitative evaluation of oxytetracycline residue and associated resistant E. coli O157:H7 in 
the meat commonly consumed in Nigerian cities on which risk assessment of antibiotics use 
in food animals in Nigeria  could be based.  The knowledge of the residue levels in such meat 
and its control would aid Nigeria‟s participation in international meat trade under the WTO.  
1.5 Study hypotheses 
(i)  HO1: There is no prudent and responsible use of antibiotics in poultry and cattle 
     production in southwest Nigeria.   
(ii)  HO2: The use of antibiotics in poultry and cattle cannot lead to the presence of high 
     levels of residue of antibiotics in meat. 
(iii) HO3: The prevalence of antibiotic residues in beef and chicken in southwest Nigeria are
     not significantly different. 
(iv) HO4: There is no significant difference in the prevalence of antibiotic residues in beef
      during dry and wet season. 
(v) HO5: The levels of oxytetracycline residue in beef during the wet and dry seasons are not
      significant different. 
(vi) HO6:  There is no significant difference in the levels of oxytetracycline residue in 
      beef and chicken in the different cities. 
(vii) HO7: The mean concentrations of oxytetracycline in beef and chicken in south western
       Nigeria are not above the codex maximum residue limits (MRLs). 
  (viii) HO8: The prevalence of beef and chicken contaminations with E. coli O157:H7 across
        the cities abattoirs are not significantly different. 
1.6 Description of study Area 
The southwest Nigeria is one of the six geopolitical zones of Nigeria. The zone comprises of 
o 1 o 1
Lagos, Ogun, Oyo, Ondo and Ekiti States and is located within latitude 6  25  to 8 03 N and 
o 1 0 1
longitude 3 02 and 5 30 E. It comprised of tropical rainforest and derived savannah 
favouring commercial livestock production. Poultry production is the major commercial 
livestock farming constituting a significant portion of commercial poultry in Nigeria and 
more than 80% of the breeders stocks in Nigeria are reared in this region. Also agro-pastoral 
Fulanis who engaged in cattle rearing are scattered across the derived savannah zone of 
southwestern Nigeria where their animals enjoy the availability of green grass and water all 
year round. Lagos Ibadan and Akure are among the state capital cities in the south western 
Nigeria (figure 1.1) were selected to have a wide cosmopolitan coverage for this work based 
on different population density and demand for meat. Poultry farming exist mostly at the 
peri-urban area and outskirts of these cities with some backyard holdings within the cities. 
Feed, equipments and veterinary inputs are located at wholesale and retail shops and feed 
mills in the cities. There is also a high concentration of government and private veterinarians 
in these cities. There are several wholesalers and retailers of livestock inputs and veterinary 
drugs in the city. Also central abattoirs (such as Araromi abattoir in Akure, Bodija abattoir in 
Ibadan and Oko-Oba abattoir in Lagos) exist along with slaughter slabs scattered within the 
cities and open meat retail markets where cattle and goats are regularly slaughtered.   
 
1.7 Limitations of study 
The kidney of chicken was not available for this study because it was not easily accessible for 
both screening and quantitative assays, Also chicken samples were not obtained from Akure 
because there were few broiler grow-out farmers and no chicken slaughter market in the city.  
 
 
 
 
 
 
 
 
 
 
 
Figure 1.1 Map of Nigeria showing the study area (southwestern Nigeria) 
 
 
 
 
 
 
 
CHAPTER TWO 
LITERATURE REVIEW 
2.1.1 Food Animal Production in Nigeria 
Food is a basic necessity of all living things and it has been identified globally as not only a 
biological need but also as an economic and political weapon. It is a potential source of 
socio-political problems in communities and nations (Friedmann, 1998). Global food security 
policies are geared towards the production and supply of adequate, nutritious, high quality, 
safe and wholesome food to the consumers (Delgado, 1999). Before the 1970's oil boom, 
agricultural exports were the backbone of the Nigerian economy with livestock products 
accounting for a significant share of exports and had a well-developed domestic agricultural 
market. However, since the advent of the oil boom, despite this sound potential for growth in 
the domestic market, Nigeria witnessed drastic decline in agricultural production, especially 
in livestock and meat sectors of the industry (Osho and Asghar, 2004). Agriculture, including 
farming and herding, accounts for 23 percent of Nigeria‟s GDP and it engages 3 percent of 
the economically active population (Blench, 1999). The livestock sub-sector accounts for 
about 20% of Nigeria‟s agriculture and it contributes about 7% of the Gross Domestic 
Product (Blench, 1999). According to David-West (1983), over 6 million transhumance 
pastoralists derive their sole livelihood from cattle and of the small ruminant‟s population in 
the northern parts of Nigeria.  Commercial poultry and piggeries are reared in peri-urban area 
near the consumer markets. 
Although current information about the country‟s livestock population and herd structure are 
not easily obtainable, it has been observed that Nigeria has a sizeable livestock population, 
which account for about 95% of her current domestic livestock intakes. In 1999, the livestock 
population in Nigeria were estimated at 19.8, 20.5, 24.3, 4.8 and 126.0 million cattle, sheep, 
goat and chicken respectively (FAO, 2000), with Nigeria taking the lead among many West 
African countries (Table 2.1).  According to Blench (1999), livestock production operations 
in Nigeria can be categorised into the following systems: 
 Traditional pastoralist system (migratory, nomadic); 
 Integrated (mixed) crop livestock system which could be at both subsistence
 or slightly above subsistence level; 
 Ranching (dairy/beef); 
 Intensive system especially for commercial dairy, piggery and poultry
 production; 
 Extensive, free range and backyard livestock production system. 
Majority of livestock in Nigeria especially cattle are reared on extensive management system 
by pastoralists or nomadic herdsmen. The distributions of livestock across the different parts 
of Nigeria depend on several factors such as climatic conditions, disease and pest prevalence, 
availability of grazing vegetation. About 80% to 90% of cattle, sheep and goats in Nigeria are 
reared by traditional pastoralists who keep these animals as a way of life without much of 
economic motivation.  Also, the indigenous chicken (Gallus gallus) constitutes about 80% of 
poultry population in Nigeria (Sonaiya, 1990) which are not economically viable to meet the 
growing protein demand of the populace. While about 20% of poultry population in Nigeria 
are reared on intensive commercial system most of which are located in the south western 
Nigeria. The south western Nigeria is the main entry point of exotic chicken and is also the 
location of major poultry breeders and retailers that distribute poultry round the country and 
beyond (Owoade et al., 2004). According to FAO (2009) Nigeria produced about 196,000 
tonnes of chicken meat annually between 1997 and 2007. This was about 50%, 7% and 
0.31% of total chicken meat produced in West Africa, Africa and the World, respectively 
(Table 2.1). 
 
Table 2.1: Livestock population (‘000) in West Africa (% for Nigeria) in 1999. 
 Cattle Sheep Goats Pigs Chicken 
Benin 1438 645 1183 470 29000 
Burkina Faso 4550 6350 7950 590 21000 
Chad 1330 1370 1070 1275 29000 
Cote d‟lvore 5582 2432 4968 23 4800 
Gambia 360 190  265 14 680 
Ghana 1273 2516 2739 352 17467 
Guinea 2368 687 864 54 8900 
Guinea- 520 280 315 340 8500 
Bissau 
Liberia 36 210 220 120 3500 
Mali 6058 5975 8525 65 24500 
Mauritania 1395 6200 4133 20 4100 
Niger 2174 4312 6469 39 20000 
Nigeria (%) 19830(39.3) 20500(36.0) 24300(35.8) 4855(57.5) 126000(36.7) 
Senegal 2960 4300 3595 330 45000 
Sierra Leone 400 350 190 52 6000 
Togo 223 740 1110 850 7500 
Subtotal 50497 57057 67896 8449 343497 
Source: FAOSTAT (2000)  
 
 
 
 
Livestock production in Nigeria provides less than 30% of minimum protein requirement of 
Nigerians due to various socio-economic constraints and agro-climatic factors affecting 
distribution and production (Blench and Marriage, 1999).  Livestock diseases are major 
limiting factors affecting productivity and profitability by increase mortality and morbidity 
rates, reduced rates of reproduction, weight gain and milk production. Apart from 
trypanosomiasis, other reported cattle diseases are anthrax, blackleg, rhinderpest, lumpy skin, 
brucellosis, papillomatosis, keratoconjunctivitis, foot-and-mouth diseases, contagious bovine 
pleuropneumonia and helminthosis (Maina, 1986). Ticks infestation is also common among 
Nigerian cattle, which lowers the fertility, skin quality, and milk and meat yields of the 
animals.  Small ruminants are afflicted by a range of diseases such as peste des petits 
ruminants (PPR), contagious caprine pleuropneumonia, heartwater, sheep pox, helminthosis, 
coccidiosis, eye infection, caseous lymphadenitis and brucellosis. Dermatophilosis attacks 
and damages the skins and hides resulting in loss of productivity and death among the 
animals and loss in foreign exchange from the famous Moroccan leather produced by the Red 
Sokoto goat. Poultry diseases like coccidiosis, chronic respiratory disease, fowl typhoid, fowl 
cholera, fowl fox, Newcastle disease and helminthosis are enzootic in Nigeria (Maina, 1986; 
Sonaiya and Swan, 2004). Nigerian livestock are therefore sustainable and renewable 
resources that can be improved to meet the challenges of the growing animal protein needs of 
over 140 millions Nigerian. 
2.1.2 Changing patterns of livestock production and consumption  
The challenges of increasing world population and the need to cater for the human nutritional 
needs in term of food supply are driving force behind intensive agriculture and cardinal 
Millennium Development Goals (MDGs).  
According to FAO (2010), agriculture including intensive livestock production will directly 
or indirectly facilitate the achievement of the following MDGs:  
Goal 1: Eradicate extreme poverty and hunger; through pursuance of adequate structure and
 practice of modern agriculture for effective household food security. 
Goal 2: Achieve universal primary education; through agriculture including crop, livestock
 and veterinary extension education on food safety.   
Goal 3: Promote gender equality and empower women; by encouraging participation of
 women in agricultural production activities  
Goal 7: Ensure environmental sustainability; good agricultural practice through irrigation, 
 soil degradation, use of mineral fertilizers, pesticides drugs and other chemicals will
 ensure sustenance of agricultural environment. 
Goal 8: Develop a global partnership for development; good agricultural practice including
 Good Practice in the Use of Veterinary Drugs (GPVD) will ensure global food trade
 such as WTO. 
In recent years, there is increased global consumption of meat, poultry and dairy products. It 
is estimated that per capital consumption in developing countries of livestock products could 
rise by as much as 40% by 2030 (FAO, 2002). Income, population movements, education, 
preferences and lifestyles are critical factors affecting dietary patterns. Throughout the world, 
there is currently major shift from consumption of basic staple diets towards more diversified 
diets with milk and other livestock products, fruits vegetables and processed foods are on 
increasing demand (Delgado, 2003).  
Meat is defined as the freshly dressed or processed tissues, mainly skeletal muscles from 
warm-blooded animals suitable for use for food (Alonge, 2005). Meat is a good source of 
essential nutrients required for growth and development, and one of the most important 
 
sources of high quality protein, vitamins and mineral (Speedy, 2003).  Pig meat is particularly 
 
rich in thiamine. Liver, and to a lesser extent kidney, are also rich in vitamin A and folic acid 
  
and in iron, riboflavin and other B-vitamins. Fish is an equally good source of protein and 
  
vitamins, including vitamins A and D in fatty fish. It also contains a well-balanced supply of
 
minerals, including iodine, and if the bones are eaten, calcium, phosphorus and fluoride. Milk 
 
is the most complete of all foods, containing nearly all the constituents of nutritional 
  
importance to man, although it is comparatively lacking in iron and vitamins C and D. It also 
 
contains substantial amounts of lactose and protein. Eggs make a useful contribution to the 
 
daily intake of vitamin D, retinol, riboflavin, iodine, iron and protein (Speedy, 2003).  
Alonge, (2005) enumerated conventional sources of meat to include cattle, lambs, sheep, 
goat, swine, camel, rabbits, horse, game like interlopes, deer, buffalo, poultry (chicken, 
ducks, geese and turkeys while the unconventional sources of Nigerian meat include Guinea 
pigs, frogs, pigeon, pheasants, grabs turtles, termites, beetle, caterpillar, giant rats, grass 
cutters, porcupine, squirrel, snail, bat, rat, mice, rainbow lizard, alligator and birds. Meat 
consumption from different species of food animals varies from country to country; culture to 
culture and religious believe.  
The average global per capital meat consumption is 52kg/year while the annual average of 
9.5kg/year was estimated for sub-Sahara Africa as against the FAO recommended per-capital 
consumption of meat of 36.4kg/year (FAO, 2002). A recent statistics showed that Nigeria‟s 
per-capita meat consumption is approximately 6.4 kilograms a year compared to China‟s is 
about 23 kg, while Canadains consume an average of 65 kg a year and the citizens of the US 
eat 95 kg. This was described as “meatcentricity” of western society (Earth Day, 2008). Alabi 
and Isah, (2002) reported that the average Nigerian consume less than 61 % of the 
recommended minimum per capita protein requirement.  In Nigeria the per capita meat 
consumption declinined from 13.8 kg in 1986 to 6.4kg in 2008 (Osho and Asghar, 2004; 
Earth Day, 2008) due to escalating increase in meat prices is a major factor (Osho and 
Asghar, 2004).  In Nigeria beef and chicken are popular staple livestock products and have 
wide consumers‟ acceptance (Gomna and Rana, 2007). Osho and Asghar (2004) also reported 
that beef and chicken are classified as luxury goods with greater proportions of these meats 
are being consumed in the cities (Udoh and Akintola, 2002).  
According to FAOSTAT (2009), the annual beef and chicken production in Nigeria 2009 was 
about 1.8 million tons which accounted for 77% total meat production in the country. FAO 
 
data showed that livestock production is growing rapidly, which is interpreted to be the result 
  
of the increasing demand for animal products. Since 1960, global meat production has more 
 
than trebled, milk production has nearly doubled and egg production has increased by nearly 
  
four times. This is attributed partly to the rise in population, as well as to the increase in 
affluence in many countries. FAO, (2000) estimated global production and consumption of 
  
meat will continue to rise from 233 million metric tons (Mt) in the year 2000 to 300 million 
 
Mt in 2020, as will that of milk, from 568 to 700 million Mt over the same period. Egg 
  
production will also increase further by 30%. The greatest increase is in the production of 
  
poultry and pigs, as well as eggs and milk (Speedy, 2003). The demand for meat in 
developing countries is growing and is expected to rise rapidly, although from very low 
consumption levels. This will stretch the capacity of existing production and distribution 
systems, but will provide income growth opportunities as well (Delgado et al., 1999; FAO 
2009) Table 2.3 and 2.4 showed the trend of production of beef and chicken meat in countries 
of the world between 1999 and 2007.  
 
 
Table 2.2: World Beef Production (1000 Tonnes) 
Countries 1994-1996 1999-2001 2005 2006 2007 
Benin 16 19 22 23 23 
Burkina Faso 67 84 106 111 116 
Cameroon 74 93 94 94 94 
Chad 62 76 82 84 86 
Côte d'Ivoire 35 33 30 31 29 
Gambia 3 3 3 3 3 
Ghana 21 23 25 24 24 
Guinea 24 32 41 44 47 
Guinea-Bissau 4 4 5 5 5 
Liberia 1 1 1 1 1 
Mali 56 66 108 106 112 
Niger 77 119 170 177 190 
Nigeria 270 285 261 284 287 
Senegal 44 46 47 50 39 
Sierra Leone 6 5 6 8 8 
Canada 948 1,263 1,464 1,327 1,279 
China 3,055 4,745 5,357 5,499 5,849 
Denmark 183 155 136 129 130 
Germany 1,437 1,346 1,167 1,193 1,186 
Netherlands 588 450 396 384 386 
World 54,068 56,304 59,493 58,758 59,852 
Source: FAOSTAT, 2009 
 
 
Table 2.3: World Chicken Meat Production (1000 Tonnes) 
COUNTRIES 1994-1996 1999-2001 2005 2006 2007 
Benin 11 12 15 16 17 
Burkina Faso 23 26 31 32 33 
Cameroon 22 27 30 30 30 
Chad 4 5 5 5 5 
Côte d'Ivoire 24 21 23 22 23 
Gambia 1 1 1 1 1 
Ghana 12 19 29 30 30 
Guinea 3 4 6 5 6 
Guinea-Bissau 1 1 1 2 2 
Liberia 5 6 8 9 9 
Mali 25 29 36 37 38 
Niger 10 11 12 14 14 
Nigeria 169 172 219 232 243 
Senegal 16 23 29 32 37 
Sierra Leone 9 10 11 11 11 
Canada 729 908 1,000 997 1,030 
China 5,783 8,695 9,964 10,164 10,617 
Denmark 158 191 183 166 170 
Germany 415 458 605 608 688 
Netherlands 611 699 628 621 610 
World 45,972 58,674 71,412 72,396 75,826 
Source: FAOSTAT, 2009 
 
 
2.1.3 World Food Situation and Safety Concerns 
There is currently global food security challenge to meet the demand of the ever increasing 
world population as affirmed during the FAO/WHO 1996 world food summit and it is also a 
cardinal millennium development goal. Concerted efforts are being made by national 
governments to increase the quantity and quality of global food supply so as to improve the 
nutritional status of populations. However, millions of people are exposed to contaminated 
food and water without access to sufficient supplies of a variety of safe, good quality food in 
many countries, even where food supplies are adequate at the national level. Almost one-
quarter of the world‟s undernourished are in sub-Saharan Africa, which is the region with the 
highest proportion of its population being undernourished (FAO, 1999).  
At the World Food Summit, governments and international organizations arrived at a 
consensus on key strategies for improving food security and nutritional status. They 
identified the major factors in world food security as constraints on food production, 
population growth, urbanization rates, changing dietary patterns, conflict and instability, 
government policy and limited investment in agriculture and research (FAO, 1996). Feeding 
the world‟s populations require coordinated and regulated interaction of the operators in 
every segment of the food chain, from the point of production, through harvesting, storage, 
processing, preservation and marketing with shared responsibility among primary producers, 
food handlers and consumers (Delgado et al. 1999; FAO, 2000). Intensification of livestock 
production through commercial enterprises is very imperative to meet global animal protein 
demand. Incidentally the global livestock sector is undergoing changes at an unprecedented 
pace over the past few decades as process termed “livestock revolution” resulting from 
booming demand in the world‟s most rapidly growing economies for food derived from 
animals has led to large increases in livestock production (Delgado et al., 1999). This has to 
be supported by major technological innovations and structural changes in the sector (FAO, 
2009) which are mostly applicable in commercial livestock production. However, millions of 
rural people still keep livestock in traditional production systems, where they support 
livelihoods and household food security.  This rapid transition of the livestock sector has 
been taking place in an institutional void as the speed of change has often significantly 
outpaced the capacity of governments and societies to provide the necessary policy and 
regulatory framework to ensure an appropriate balance between the provision of private and 
public goods. FAO (2009), affirmed that several systemic risks and hazards associated with 
the growth and transformation of livestock industry has outpaced the capacity and willingness 
of governments and societies to control and regulate this sector. The control of diseases in 
animals is an important component of livestock production. Consequently, antibiotics and 
other drugs are frequently used in the production of food animals.  
2.2 Antibiotics  
Antimicrobial substance is any substance of natural, semi synthetic or synthetic origin that at 
in vivo concentrations kills or inhibits the growth of microorganisms by interacting with a 
specific target (Cerf et al., 2010).  
2.2.1 Historical Overview of Antibiotics 
During the second half of nineteenth century Robert Koch observed that some 
microorganisms could destroy others (Koch, 1876). This phenomenon was confirmed by 
Louis Pasteur, (1880) who believed it could be utilized in medicine. This was followed by 
discovery of the first “chemical cure” for a disease by Paul Ehrlich which was arsenical 
compound called arsphenimine (marketed as Salvarsan®) that was selectively toxic for 
Treponema  pallidium (Erhlich and Hata, 1910). The period of 1920s and 1960s became the 
era of wonder drugs known as antibiotics; in 1935, the German bacteriologist and 
pharmacologist Gerhard Domagk discovered that the dye, protonsil red used to tint cloth was 
effective in the treatment of streptococcal infections in mice (Domagk, 1935). When his 
young daughter was dying of streptococcal infection, in desperation he injected this dye into 
to the girl and her fever dropped almost immediately, this quick recovery at that time was 
termed as nothing short of miraculous. It was a Swiss-born Chemist, Daniel Bovert, who later 
showed that the antibacterial activity of protonsil red was caused by sulphanilamide 
component of the dye and by 1940 sulphanilamide was available under at least thirty three 
different trade names (Magner, 1992). 
The discovery of penicillin by Alexander Fleming in 1928 was the starting point of modern 
antibiotic therapy.  Alexander Fleming, an English bacteriologist returned from holiday to his 
laboratory at St. Mary‟s hospital in London by early September 1928 where he made his 
famous observation on an old, uncovered culture plate of bacteria. He noticed a blue-green 
mould that was attacking the bacteria. He identified the mould as Penicillium notatum, 
cultured it in nutrient broth, filtered it and observed in the filtrate (which he named 
“Penicillin”) a substance that ravaged bacteria. Fleming reported this accidental discovery to 
the scientific world in the British Journal of Experimental Pathology (Fleming, 1929). 
Fleming was recognised for this landmark discovery and was awarded Nobel Lauret in 
Medicine in 1945 (http://nobelprize.org/medicine/laureate/1945). 
The term antibiotics (from Greek words that literally means against life anti – means against, 
biosis – means life) first appeared in scientific literature in 1942 (Waksman et al., 1942) was 
coined by Selman Blaksman to embrace those newly discovered antimicrobial substances 
such as pyocyanin, penicillin, actimycin and others, Waksman used this term to describe and 
define those substances of microbial origin that specifically inhibit the growth of other 
microorganisms. The usage for this term has now been extended to include any low 
molecular weight metabolites from living organisms or synthetic compounds which at low 
concentrations will kill or inhibit the growth of other organisms (Greenwood and O‟Grady, 
1997). 
According to (Lancini et al., 1995), antimicrobial agents affect the growth of bacteria either 
by killing bacteria cells with or without the lysis or rupture does not occur are known as 
bacteriocidal or by inhibiting cell wall and cytoplasmic membrane synthesis thereby 
inhibiting their growth and are known as bacteriostatic. 
Antibiotics that kill or inhibit the growth of wide groups of bacteria (both Gram-negative and 
Gram-positive) are called broad spectrum antibiotics while those that act only on a single 
group of bacteria (either Gram-negative or Gram-positive) are narrow spectrum antibiotics. 
Majority of antibiotics used in human and veterinary medicine are “natural product” 
elaborated as secondary metabolites by living organisms primarily bacteria and fungi (Bennet 
and Bentley, 1989; Davies, 1990; Vining, 1990). Most antibiotics are products of secondary 
metabolism of three main groups of microorganism: Actinomyces, Eubacteria and 
filamentous fungi (Greenwood, 2009). The actinomyces produce the largest number and 
greatest variety of known antibiotics, with more than six thousand active substance isolated 
from them (Greenwood, 2009). 
2.2.2 Classification of Antibiotics 
There are several methods used to classify and group antibiotics. They are grouped together 
based on their source, mechanism of action, chemical structure and spectrum of activity 
(Lancini, et al., 1995; Greenwood and Whitney, 2009). They are also classified as broad or 
narrow spectrum, depending on the range of bacterial species against which they are active, 
or as bacteriostatic or bactericidal on the basis of their mechanism of action. An antimicrobial 
that exhibits a large dilution difference between inhibitory and bacteriocidal effects is 
considered to be a bacteriostatic drug. An antimicrobial that kills the bacterium at or near the 
same drug concentration that inhibits its growth is considered to be a bactericidal drug 
(Greenwood and Whitney, 2009). In general, antibiotics and other chemotherapeutic agents 
are grouped together based either on their mechanisms of action and more usually chemical 
structure (Lancini, et al., 1995). Figure 2.1 shows the chemical structures of some antibiotics. 
2.2.3 Mode of action of Antibiotics 
Since the discovery of antibiotics much knowledge has been acquired on their mode of action 
and it is a major basis for their choice in the treatment of man and animals (Lancini, et al., 
1995).  Antibiotics can be classified into several groups according to their mode of action on 
or within bacteria (Lancini, et al., 1995; Millodot, 2009): 
 Inhibiting bacterial cell wall synthesis, such as bacitracin, vancomycin and the β-
lactams based agents (e.g. penicillin, cephalosporins).  
 Drugs affecting cytoplasmic membrane, such as polymyxin B sulfate and gramicidin.  
 Drugs inhibiting bacterial protein synthesis, such as aminoglycosides (e.g. amikacin 
sulfate, framycetin sulfate, gentamicin, neomycin sulfate and tobramycin), 
tetracyclines, macrolides (e.g. erythromycin and azithromycin) and chloramphenicol.  
  Drugs inhibiting the intermediate metabolism of bacteria, such as sulfonamides (e.g. 
sulfacetamide sodium) and trimethoprim. 
  Drugs inhibiting bacterial DNA synthesis, such as nalixidic acid and 
fluoroquinolones (e.g. ciprofloxacin, levofloxacin, moxifloxacin, norfloxacin and 
ofloxacin).  
 Other antibiotics such as fusidic acid, the diamidines, such as propamidine isethionate 
and dibrompropamidine. Syn. antibacterial. 
 
 
 
 
 
 
 
 
 
 
Figure 2.1: Chemical Structures of Some Antibiotics 
   
 
 
 
 
 
 
 
2.2.4 Metabolism of antibiotics 
Pharmacokinetics describes how the drug behaves in the body, i.e. absorption, distribution, 
metabolism and elimination, as reflected in the time course of drug concentrations in plasma 
or tissue (Chopra et al., 1992; Chopra and Roberts, 2001). After each administration of an 
antimicrobial drug, the distribution and concentrations in the body compartment depend on 
certain key the pharmacokinetic variables such as; the maximum plasma concentration, the 
peak time plasma concentration, the area under the plasma concentration time curve, the 
volume of distribution, and the plasma half-life. Most veterinary drugs are metabolized in the 
body to produce more water soluble compounds, which are more readily excreted (Aerts et 
al., 1995). For example, penicillins are eliminated almost entirely by the kidneys, which 
results in very high concentrations in the urine, (Prescott, 2000b). Penicillin-G is metabolized 
to some extent by hydrolysis of the β-lactam ring, and the metabolites are microbiologically 
inactive (Prescott, 2000b). Most tetracyclines are excreted unchanged in urine and, to a lesser 
extent, bile (Prescott, 2000b). Oxytetracycline is not metabolized to a significant extent in the 
body; it is eliminated in the urine and faeces (Spoo, 1995). High concentrations of 
fluoroquinolones are found in organs of excretion Aminoglycosides are eliminated 
unchanged by renal excretion (Prescott, 2000a). Chloramphenicol is excreted mainly in the 
form of a microbiologically inactive glucuronic acid conjugate (Glazko et al., 1977). 
The highest free drug concentrations of most antimicrobials are found in kidney and renal 
pelvis (Aerts et al., 1995). After intramuscular administration of oxytetracycline to cattle, the 
injection sites and kidneys contained the highest residue concentrations followed by the liver, 
hence oxytetracycline concentrations in edible tissues could be predicted from kidney cortex 
concentrations, whereas renal penicillin-G concentrations did not correlate with muscular 
drug concentrations (Black and Gentry, 1984). Aminoglycosides are usually found in tissues 
in low concentrations and unbound, except in the renal cortex where they tend to concentrate 
(Isoherranen and Soback, 1999). Incidence of false positive reactions and varying ratios of 
residue concentrations in kidney and muscle of healthy and diseased animals (Nouws, 1984; 
Engel et al., 1983) complicate the use of kidney tissue as the test matrix. 
2.2.5 Antibiotic Resistance 
The term antibiotic resistance is often used in a general sense to signify the lack of effect of 
antibiotic agent on a bacteria cell. The phenomenon antibiotic resistance occur when bacteria 
strains derived from species that were susceptible to certain antibiotics are no longer inhibited 
by the minimal concentration of the antibiotic that inhibit, the growth of typical strains of that 
species (Greenwood, 1995).  The resulting resistance is dependent on the interaction among a 
given bacterial strain, the particular antibiotic and the concentration of the antibiotic (Lancini 
et al, 1995). A bacterial strain is considered truly resistant to a given antibiotic only if it can 
grow in the presence of a concentration equal to or greater than that which antibiotic can 
reach in the serum or tissue (Drlica, 2001). Antibiotic resistance in clinical bacteriology has 
been recorded since these agents first came into use. The first antibiotic resistance mechanism 
was identified in 1940 when Abraham and Chain described the presence of a penicillinase, an 
enzyme that inactivates penicillin, in resistant Escherichia coli (Abraham and Chain, 1940) 
and a similar mechanism penicillin resistance was reported in 1944 in an isolate of 
Staphyloccocus aereus (Kirby, 1994). The enormity and complexity of the current problem of 
antibiotic resistance have earlier been fore told in the early days of antibiotic discovery when 
Alexandar Flemming recognized the threat and factors that would promote resistance 
(Fleming, 1929). Over the last three decades there has been concern over the problem of 
antibiotic resistance pathogens, evidence is mounting that antibiotic-resistant enteric bacteria 
(for example, Escherichia coli, Salmonella, Campylobacter and Enterococci) can transfer 
from animals to man via the food chain or by direct contact, leading to the establishment of a 
community reservoir of resistance genes (Van den Bogaard and Stobberingh, 1999). There 
are increasing reported numbers of bacterial infections that fail to respond to antibiotic 
treatment (Levy, 1992).  WHO, CDC, FDA, EUCVM and many public health agencies  are 
concerned  that antibiotic resistance is “a growing menace to all people,”  noting  that 
continued spread of resistance means that treatments for common infections “will become 
increasingly limited and expensive and, in some cases, non-existent.”  
Bacteria reproduce rapidly, sometimes in as little as 20 minutes hence, it does not take long 
for antibiotic-resistant bacteria to spread (Levy, 1997). Microorganisms display amazing 
versatility in terms of their ability to avoid, withstand, or repel the antibiotic onslaught (Neu, 
1992; Courvalin, 1994). Often, the use of antibiotics disrupts the delicate bacterial ecology 
within the body of humans and animals thereby allowing the proliferation of resistant species 
and sometimes initiating new infections that are worse than the one originally treated (Levy, 
1997). The historical cycle that has been witnessed in the last fifty years is that as drugs were 
discovered and diseases successfully treated with certain antibiotics soon the organisms 
develop resistance (Levy, 1992). Antibiotic resistance makes diseases like cholera, bacterial 
meningitis, tuberculosis, pneumonia, and even plagues to reemerge a renewal vengeance 
(Neu, 1992; Caputo et al, 1993; Doern et al., 1996). 
2.2.5.1: Resistance Mechanisms, Cross-Resistance and Co-Selection 
Resistance to an antibiotic may be an inherent property of the infecting organism or it may be 
acquired. The intrinsic resistance is a natural property of the bacteria resulting from mutation 
or acquisition of new genetic material (Kathleen et al., 2003). Intrinsic resistance refers to 
bacteria in their natural state are insensitive to an antibiotic without acquiring resistance 
factors. Mutations that result in antibiotic resistance are spontaneous events involving 
changes in chromosomal nucleotide sequences. The development of mutational resistance is 
favoured by low and intermittent drug dosage (Prescott and Baggot, 1993). Acquired 
resistance may result from mutation or from transfer of an extrachromosomal genetic material 
followed by selection of resistant organisms during therapy (Neu, 1992).   
An acquired resistance gene induces a resistance mechanism if this gene is expressed. 
Resistance mechanisms can be either constitutive or inducible, depending on whether the 
resistance gene is can be expressed in the presence of the antimicrobial drug (Catry et al., 
2003). The different resistance mechanisms are related to the mechanisms of action of 
different antimicrobial drugs on the bacterial cell, but more than one resistance mechanism 
can be present in a given bacteria.  
The most important resistance mechanisms are antimicrobial drug modification, reduced 
intracellular accumulation, and modification of the target site (Livermore, 1995). 
Antimicrobial drug modification consists of an enzymatic modification or inactivation of the 
antimicrobial drug that prevents the molecule from reaching the target site. The inactivation 
of penicillins and cephalosporins by β-lactamases (Livermore, 1995) and of aminoglycosides 
by acetyl-, adenyl- and phospho-transferases (Davies, 1994) in both Gram-positive and 
negative species are examples of enzymatic inactivation. The second mechanism arises from 
an alteration in bacterial cell-wall porins, resulting in either a decreased uptake or an 
increased removal of the antimicrobial drug in the cell. The reduced intracellular 
accumulation inhibits the antimicrobial drug from proceeding with its normal intracellular 
action. An increased removal of tetracyclines, for example, can be caused by the presence of 
tetracycline efflux genes, e.g. tet (A-E), which are found in a wide variety of bacteria 
(Roberts, 1996). The third resistance mechanism results from a chemical modification of the 
target site. For instance, mutations in the genes for DNA gyrase and topoisomerase can cause 
structural changes that inhibit fluoroquinolones from binding to these target sites (Webber 
and Piddock, 2001). Finally, a fourth but less prevalent mechanism is based on a bypass 
effect that prevents the inhibitory action of the antimicrobial drug. This is a well-known 
resistance mechanism for the combination of sulphonamides with trimethoprim. In this case 
an alternative synthetic pathway for folic acid production makes the microorganism 
unsusceptible to the antimicrobial drug combination. 
The most common and important process of resistance transfer is conjugation in which two 
organisms exchange R-plasmids by contact through sex pilus. R-factors may also be released 
by one bacterium and take in through the cell wall of another (transformation). R-factors, 
therefore, can circulate in humans, in animals and in the environment and possibly between 
animals and humans (Landicho, 1996). Transmission of antibiotic resistance in pathogenic 
bacteria may cause zoonotic infections, while resistant non-infectious bacteria may serve as a 
reservoir of R-plasmids for other virulent organisms. R-factors encode at least four different 
biochemical mechanisms: enzymatic degradation; alteration of the antibiotic by the cell, 
alteration of the target site of the antibiotic and synthesis of a resistant form of an essential 
metabolic enzyme that is normally sensitive to different antibiotics (Timoney et al., 1988). 
Cross-resistance arises from a resistance mechanism that makes bacteria resistant to more 
than one antimicrobial drug. This is often true for different molecules of a given class of 
antimicrobial drugs, such as tetracyclines, because they are structural analogues. For instance, 
tet (M) genes induce resistance to oxytetracycline, doxycycline, chlortetracycline and 
minocycline (Roberts, 1996). In contrast, multi-drug efflux pumps (mex) genes can cause 
cross-resistance to a wide range of structurally heterogeneous toxic compounds, including 
antimicrobial agents (Paulsen, 2003). Cross-resistance can also occur if analogue 
antimicrobial drugs act on the same target site of a microorganism. The presence of one erm 
(X) gene causes resistance against macrolides, lincosamides and B-compounds of the 
streptogramins. In livestock this gene has been found in streptococci of the bovine udder and 
pneumonic lungs from swine, and in faecal enterococci of different animal species (Butaye, 
1998; Martel et al., 2001). Such solitary genes causing cross-resistance, or different 
resistance genes gathered on a single mobile genetic element (transposons or plasmids), may 
cause co-selection (Schwarz et al., 2001). With co-selection, resistance to several different 
antimicrobial drugs emerges while only one antimicrobial drug is used. Thus the importance 
of co-selection is substantial. Levy et al. (1976) clearly demonstrated co-selection in caecal 
coliforms of poultry. Tetracyclines given orally made the bacterial caecal flora less 
susceptible not only to tetracyclines, but also to ampicillin, streptomycin and sulphonamides. 
Bager et al. (1999) also observed a significant difference between Danish swine and poultry 
in the persistence of glycopeptide-resistant enterococci (GRE) after the ban on avoparcin 
(glycopeptide) as a growth promoter. In poultry, the level of GRE decreased from 80 to 10%, 
while during the same period the percentage of GRE in swine declined from 25 to 20%. The 
vanA gene, selected by the use of tylosin because of linkage with the ermB gene, maintained 
the glycopeptide resistance level (Aarestrup, 2000). 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 2.2: Mechanisms of Action of Antibiotics 
 
 
 
 
 
 
 
 
 
2.2.5.2 Vectors of Antibiotic Resistance 
Bacteria have evolved very sophisticated means of exchanging DNA, both within their own 
genus and species and across themselves. Foreign genes responsible for antibiotics resistance 
reside on mobile genetic elements such as plasmids, transposons and integrons. 
2.2.5.2.1 Plasmids 
Plasmids are extra-chromosomal resistance circular self replicating DNA molecules that are 
produced in bacterial cells (Thomas, 2000) they can replicate independent of the bacterial 
chromosomal DNA. Plasmids are one of the key players in the team of mobile genetic 
elements that fuel bacterial adaptability and diversity. Plasmids are capable of promoting the 
rapid speed of antibiotic resistance genes. They can exist in the autonomous extra-
chromosomal state or can be inserted into the bacterial chromosome and then be carried as 
part of it (Thomas, 2000). Plasmids can be divided into two macro groups: narrow and broad 
host range or promiscuous plasmids. Broad host range plasmids are defined as those for 
which replication is not restricted to one particular species of bacteria but can replicate in 
many of a selected group of host species (Valla, 1998). Broad host range plasmids may 
further be subdivided into two subgroups: conjugative or self-transmissible and non 
conjugative but mobile. The self-transimisible, broad host range plasmids are the most active 
vehicle for a potential “horizontal gene pool” of antibiotic resistance genes that are available 
to many bacteria (Thomas, 2000). 
2.2.5.2.2 Transposons 
Transposon is a genetic element capable of moving from one DNA molecule to another, 
independent from the normal reaA-dependent type of combination. Transposons are linear 
pieces of DNA that range in size from 2.5 to 23 kilobase pairs (kb) and contain two identical 
insertion sequences (Iselements), one at each end of the molecule. Following the discovery 
R-factors, many antibiotic resistance genes were found to be located on small pieces of DNA 
that can independently move around (Hedges and Jacob, 1971).  Transposons appear to be 
ubiquitous in nature and have been identified in many types of organisms including plants 
and animals, as well as bacteria (Berg and Howe, 1989; Sherrat, 1989). There are several 
classes of transposons, grouped according to their general structural and functional 
organization, using features such as size, conserved DNA regions, number of open reading 
frames (ORFs), presence of the host genes and particularly the transpositional pathway (Nield 
et al., 2001). Some transposons, such as Tn10, which encode resistance to tetracycline, move 
in a “conservative” manner, without replication (Kleckner, 1989). Conjugation transposons, 
found in many gram-positive and a few gram-negative bacteria, are integrated DNA segments 
that excise from the chromosome to form a circular intermediate which then transfers itself to 
a recipient, where it integrates once again into the chromosome (Salyes and Shoemaker, 
1997). Conjugation transposons resemble plasmids in that they are transferred by conjugation 
and have a circular intermediate, but do not replicate (Salyers and Shoemaker, 1997). 
2.2.5.2.3 Integrons  
The term integron was originally coined to describe the group of apparently mobile elements 
that contain one or more antibiotic resistance genes located at a specific site as well as 
contain the determinants of the site-specific or recombination system responsible for insertion 
of the resistance genes (Stoke and Hall, 1989).  Integrons are “nature” vectors gene-capture 
and expression systems (gene cassettes) for exogenous DNA that incorporate open reading 
frames (OFR) and convert them into functional gene (Ploy et al., 2000).  They possess 
conserved region that codes an integrase (Int) and a variable region (5´CS-3´CS) where 
various resistance cassettes can be integrated themselves (Rodriguez, 2006). More than sixty 
different antibiotic resistance genes to most commonly used antimicrobial drugs have been 
characterized in cassette structure (Mazel and Davies, 1998). Carattoli (2001), reported that 
integrons are found among the genetic element and contributed to the development of 
antimicrobial multi-resistance in Gram-negative bacteria.  
2.2.6 Determination of Antibiotic Resistance 
Antimicrobial resistance have been conventionally determined using cultural broth- and agar-
based antimicrobial susceptibility testing methods to provide a phenotypic profile of the 
response of microbial pathogens to an array of antimicrobial agents (Pfaller, et al., 2001). 
Antimicrobial susceptibility is to guide the clinician in the choice of appropriate agents for 
therapy or used to evaluate the in vitro activity of new agents.  
The three phenotypic methods commonly used are, disc diffusion, minimum inhibitory 
concentration (MIC) or minimum bactericidal concentration (MIB) determination and 
Breakpoint methods (Jones and Pfaller, 1998). The protocols based on microbial cultural 
technique are described and standardised by National Committee for Clinical Laboratory 
Standards (NCCLS, 2004). Antimicrobial susceptibility are usually reported qualitatively as: 
sensitive (S), which indicates that the standard dose of the agent should be appropriate for 
treating the patient infected with the strain tested; resistant (R), which indicates that an 
infection caused by the isolate tested is unlikely to respond to treatment with that 
antimicrobial agent; and intermediate (I), where the strains are moderately resistant or 
moderately susceptible and indicates that the strain may be inhibited by larger doses of the 
agent or may be inhibited in sites where the agent is concentrated (e.g. urine). Quantitative 
testing determines the MIC, which is the lowest concentration of the agent that will prevent a 
microbial population from growing. The minimum bactericidal concentration (MBC) is the 
lowest concentration that kills 99.9% of the population.  
However, due to the rapid emergence, dissemination and global threat of bacterial resistance 
there has been need to pursue molecular typing of resistant strain of these bacteria. This is a 
critical tool for effective surveillance and intervention against the menace of resistance 
(Diekema, et al., 2000). Comprehensive molecular typing of organisms collected in a global 
surveillance program will helps to provide information regarding the emergence and 
distribution of specific pathogenic strains as well as the spread of resistance determinants. 
Table 2.5 shows the some of the molecular methods used in antimicrobial active surveillance 
program (Pfaller et al., 2001). 
 
 
 
 
 
 
 
 
 
 
 
 
 
Table 2.4:  Molecular typing antibiotic resistance methods. 
Method Comments Examples 
Plasmid analysis Plasmids may be digested Staphylococci, 
with restriction Enterobacteriaceae 
endonuclease enzymes; 
useful in tracking spread of 
resistance genes 
Restriction endonuclease analysis of Large number of bands; Enterococci, 
chromosomal DNA with conventional difficult to interpret; not Staphylococcus 
electrophoresis amenable to computer aureus, Clostridium 
analysis; a comparative difficile, Candida 
typing method only species 
Genome restriction fragment-length Fewer bands; amenable to Enterobacteriaceae, 
poly- morphism analysis: ribotyping, automation and computer staphylococci, and 
insertion sequence probe fingerprinting analysis; sequence based Pseudomonas 
profiles; library typing aeruginosa, 
methods Candida species 
PCR-based methods: repetitive- Crude nucleic acid extracts Enterobacteriaceae, 
elements PCR spacer typing, selective and small amounts of DNA Acinetobacter 
amplification of genome restriction may suffice; amenable to species, 
fragments,multilocus allelic sequence- computer analysis staphylococci 
based typing 
Pulsed-field gel electrophoresis (PFGE) Fewer bands; amenable to Enterobacteriaceae, 
automation and computer staphylococci, 
analysis; sequence based enterococci, 
profiles; library typing Candida species 
methods 
 
 
 
 
 
 
2.2.6 Antibiotic Residues in Food Animals 
Consumers of animals and animal products (meat, milk, eggs, etc.) are liable to ingest 
whatever chemicals the animal has consumed or been exposed to veterinary drugs, and also 
insecticides used on the animal, herbicides and fertilizers used on pastures and chemical 
additives used in its feed. Some of these substances are toxic (in particular, pesticides and 
herbicides), and some are undesirable in other ways for use on animals whose products are 
consumed by humans.  Residues of veterinary drugs may exert adverse effects on consumers 
in a number of ways, such as; chronic toxicological adverse effects, acute pharmacological 
effects on consumers and on the microflora of the gastrointestinal tract of consumers and 
allergic reactions (Sundlof et al., 2000; Berends et al., 2001; Doyle, 2006). The two main 
major substances of public health concern on drug use in food animal production are 
hormones and antibiotics. Several concerns regarding antibiotics use in animals result from 
the development of  bacterial resistance genes that are transferable to human beings, the 
effect on human intestine microflora composition, potential allergic reactions in sensitized 
individuals, direct toxicity and technological problems of their residues in meat and milk 
products (Stark, 2000).  
2.2.6.1 Tetracyclines Residue 
Tetracyclines are broad-spectrum antibiotics discovered in the 1940s and are used to treat a 
variety of bacterial, protozoan and rickettsiae infections, also as growth promoter in animals 
(Chopra and Roberts, 2001). In studies with humans, about 60% of an ingested dose of 
oxytetracycline was absorbed from the gastrointestinal tract and was then widely distributed 
in the body, particularly to liver, kidney, bones and teeth (Agwuh and MacGowan, 2006). 
There appeared to be little, if any, metabolism of this drug in humans or animals and it was 
primarily excreted in the urine (Agwuh and MacGowan, 2006; JECFA, 2003). At therapeutic 
doses, tetracyclines are occasionally associated with discoloured teeth, allergic reactions, or 
peripheral blood changes (Waltner-Toews and McEwen, 1994). Subtherapeutic dosages as 
low as 2mg/l of oxytetracycline administered over seven days resulted in increased drug-
resistant enterobacteriaceae (Corpet, et al., 1996). A no-observed-effect level residue of 
tetracycline of 2 mg/person/day was observed. There have been reports of allergic reactions 
to tetracyclines (Waltner-Toews and McEwen 1994). The CAC recommended MRLs of 
tetracyclines in kidney, liver, egg, muscle and milk of food animals destined for human 
consumption are 1200, 600, 400, 200, and 100 μg/kg respectively (CAC, 2009).  The ADI of 
0-30 μg/kg bw for tetracycline, oxytetracycline and chlortetracycline (group ADI) was 
established (JECFA, 2003). Oxytetracycline is used by, and JECFA (2003) as the marker 
residue to determine acceptable levels of intake because it is found to induce antibiotic 
resistance among the coliform bacteria in the human intestine. Liquid chromatographic 
techniques are the official methods widely recommended for confirmation of tetracycline 
residue levels in these food items (MacNeil et al., 1996; Posyniak et al., 1999; CAC, 2009).  
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
2.2.6.2 Causes of antimicrobial residues in meat 
The major reported cause of violative levels of veterinary drugs in food is failure to observe 
and adhere to the recommended withdrawal periods (van Dresser and Wilke, 1989; Kukanich 
et al., 2005). Improper maintenance of treatment records or failure to identify treated animals 
adequately can also lead to their omission (Sundlof, 2000). Results by FSIS National Residue 
Monitoring Plan indicated that penicillin and sulfonamide drugs, Neomycin and gentamicin 
were commonly detected at violative levels in cattle, swine and poultry (FSIS, 2006). Other 
drugs detected in cattle and swine included tilmicosin, flunixin, and tetracyclines. Faecal 
recycling, where the drug excreted in faeces of treated animals contaminates the feed of 
untreated animals, can be the cause of residues of certain antimicrobial groups (McCaughey 
et al., 1990). Housing of un-medicated pigs in boxes where pigs had previously been treated 
orally with sulfamethazine resulted in residues in urine, kidney and diaphragm (Elliott et al., 
1994). Violative drug residues can also occur as a result of improper use of a licensed product 
or through the illegal use of an unlicensed substance or extralabel dosages and use (Kaneene 
and Miller, 1997; Higgins et al., 1999). Residues can also occur in calves fed milk and/or 
colostrum from cows receiving antimicrobials (Guest and Paige, 1991). In most countries β-
lactams are widely applied in mastitis therapy and are consequently the major reason for the 
presence of inhibitory substances in milk (Sternesjö and Johnsson, 1998). 
The disease status of an animal and the way in which drugs are administered also influence 
the potential for residues as they affect the pharmacokinetics of the drugs, metabolism, or the 
presence of infection and/or inflammation may cause the drug to accumulate in affected 
tissues (Kaneene and Miller, 1997). Subcutaneous and intramuscular administrations increase 
the potential for residues at the injection sites (Kaneene and Miller, 1997; Berends et al., 
2001). Secondary drug concentration peaks in plasma have been detected after subcutaneous 
injections of benzathine procaine penicillin.  
Contamination of feeding stuffs could also be an important source of unintended application 
of antimicrobials (McEvoy, 2002). In a survey carried out in Northern Ireland antimicrobials 
were detected in 44% of feeds declared by the manufacturers to be free of medication (Lynas 
et al., 1998). Residual quantities of medicated feed may be retained at various points along 
the production line, contaminating subsequent batches of feed as they are processed 
(Kennedy et al., 2000). Data from a sulfamethazine residue programme suggested that 25% 
of violations were due to inadequate cleaning of feed mixers (Guest and Paige, 1991). 
 
 
2.2.6.3 Public health risks of antimicrobial residues 
Antimicrobial residues in foods of animal origin may cause problems for several reasons. In 
addition to toxic effects, effects on intestinal microbiota and the immune system are 
important (Perrin-Guyomard et al., 2001; Doyle, 2006). Microbiological endpoints are 
considered more valid and sensitive in the safety evaluation of antimicrobial residues in 
production animals than standard toxicological endpoints (Boisseau, 1993). 
2.2.6.4 Effects of residues on gut microbata 
The microbiota in gastrointestinal tract of man and animals are extremely complex, yet 
relatively stable, ecological community, containing more than 400 bacterial species (Carman 
-1
et al., 1993). The concentration of anaerobic microbiota is 1011-1012 CFU g  faeces, and the 
concentration of aerobic microbiota much lower i.e. less than 0.1% of the normal microbiota 
consists of aerobes (Vollaard and Claesner, 1994). In addition to the resident dominant 
anaerobic microbiota, the microbiota consists of a subdominant microbiota, a resident 
minority microbiota and a variable microbiota composed of bacteria which may be present 
for a variable period of time (Boisseau, 1993). Colonisation resistance means the natural 
defence by normal microbiota against colonisation and translocation by exogenous 
potentially pathogenic microbes or against the overgrowth of indigenous opportunistics 
(Corpet, 1993; Berends, et al., 2001). Administration of antimicrobial agents may cause 
disturbances in these functions (Nord and Edlund, 1990). The extent of disturbances in the 
ecological balance between host and microorganisms occur depends on the spectrum of the 
antimicrobial agent, the dose, pharmacokinetic and pharmacodynamic properties, and in-vivo 
inactivation of the agent (Wegener et al., 1999; Sullivan et al., 2001). 
Four microbiological endpoints have been identified that could be of public health concern: 
modification of the metabolic activity of microbiota, changes in bacterial populations, 
selection of resistant bacteria, and perturbation of the barrier effect (Boisseau, 1993; 
Gorbach, 1993; Sundlof et al., 2000; Perrin-Guyomard et al., 2001). In cases of reduced 
colonisation resistance not only are the minimal infectious or colonisation doses of 
pathogenic or resistant bacteria considerably lower, but animals also excrete these bacteria in 
higher numbers and over a longer period of time compared to animals with an intact 
colonisation resistance (van den Bogaard and Stobberingh, 1999; 2000). Low doses of 
antimicrobial drugs could alter intestinal enzyme activity and have an effect on microbiota 
ecology (Gorbach, 1993). 
2.2.6.5 Hypersensitivity effects of antibiotic residues 
Antimicrobial drug residues in animal tissues may cause hypersensitivity reactions in 
humans. Drug hypersensitivity is defined as an immune-mediated response to a drug agent in 
a sensitized patient, and drug allergy is restricted to a reaction mediated by IgE (Riedl and 
Casillas, 2003; Gomes and Demoly, 2005). Drugs are foreign molecules, but their molecular 
weight is usually too small to be immunogenic. For drugs to be immunogenic, they must act 
as haptens, which must combine with carrier proteins to be immunogenic and elicit antibody 
formation (Dewdney et al., 1991). An allergic reaction may be triggered by antimicrobial 
residues in a previously sensitized individual. In relation to primary sensitization, it is 
unlikely that residues could contribute to the overall immune response in view of the very 
low concentrations that are likely to be encountered. More so, the duration of exposure is also 
short (Dewdney et al., 1991; Sundlof et al., 2000). All antibiotics have the potential to cause 
allergic reactions; penicillins are most commonly implicated, affecting up to 10% of people 
receiving these drugs therapeutically (Dayan, 1993). Notwithstanding their non-toxic nature, 
β-lactams appear to be responsible for most of the reported human allergic reactions to 
antimicrobials (WHO, 1991;  Fein et al., 1995). Angioneurotic oedema and tightness of chest 
due to penicillin residues in meat was reported by Schwartz and Sher (1984). Also, in one 
study of 15 people known to be very sensitive to penicillin found that three reacted after 
drinking milk containing a total of 2.5 μg penicillin, and two sensitive volunteers developed 
rashes after eating pork containing 0.02–0.04 ppm penicillin (Dayan, 1993).  Anaphylactic 
reactions to penicillin in pork and beef have also been reported (Kanny et al., 1994; Raison-
Peyron et al., 2001). Also one case of anaphylaxis was possibly caused by streptomycin 
residue was reported by Tinkelman and Bock, (1984).  Aminoglycosides, sulphonamides and 
tetracyclines may also cause allergic reactions (Paige et al., 1997). Certain macrolides may be 
responsible for liver injuries, caused by a specific allergic response to macrolide metabolite-
modified hepatic cells (Dewdney et al., 1991). Adverse reactions to antibiotics have been 
linked to hypersensitivity (Woodward, 1991) and cases of chronic urticaria (Dayan, 1993). 
Minor reactions such as urticaria, due to exposure to allergenic residues are often not usually 
associated and reported (Woodward, 1991). 
2.2.6.6 Other harmful effects of antibiotic residues 
Hazards of chloramphenicol include  non-dose related aplastic anemia, reversible suppression 
of the bone marrow, gray baby syndrome (causing circulatory collapse in children less than 
30 days) and irreversible, idiosyncratic (Schmid, 1983; WHO, 1988; Waltner-Toews and 
McEwen, 1994). Aplastic anemia (fatal blood dyscrasia) can occur in sensitised individuals 
exposed to concentrations of chloramphenicol that might remain as residues in edible tissues 
of chloramphenicol-treated animals (Settepani, 1984). Aminoglycosides residue can produce 
damage in urinary, vestibular and auditory functions (Shaikh and Allen, 1985). Also the 
residue of furazolidone and its metabolites have been shown to be highly carcinogenic hence, 
its FDA approval was withdrawn in 1991 and NFDAC placed a ban on it use in Nigerian 
livestock since 1996 (NAFDAC, 1996) 
 
2.2.7 Safety factors for the evaluation of antimicrobial drug residues 
To assess the safety of ingested antimicrobial residues national and international committees 
evaluate data on chemical, pharmacological, toxicological and other, e.g. antimicrobial, 
properties of the drugs derived from studies of experimental animals and observations in 
humans (Woodward, 1998). The Joint FAO/WHO Expert Committee on Food Additives 
(JECFA) of Codex Alimentarius Commission undertakes the safety evaluation of residues of 
veterinary medicines. In the safety evaluation of veterinary drugs tests undertaken to 
demonstrate the safety of the substance are performed in order to determine a no observed 
adverse effect level (NOAEL). This level is the basis for calculating an acceptable daily 
intake (ADI). After an ADI has been determined, maximum residue limits (MRLs) are 
determined for various food commodities so that overall residue intake remains below the set 
ADI in a standard food basket. In order to ensure that drug residues have declined to a safe 
concentration in various tissues, a specified period of drug withdrawal is set for a veterinary 
medicinal product. In the European Union (EU) maximum residue limits (MRLs) must be 
established for all pharmacologically active substances for the concerned animal species and 
relevant tissues or products. These MRLs are the basis for the determination of limits of 
detection (LODs) of various analytical methods used in residue surveillance. In the EU safety 
evaluation of residue is performed by the Committee for Veterinary Medicinal Products 
(CVMP) of the European Agency for the Evaluation of Medicinal Products (EMEA), while in 
the USA by Food Safety and Inspection Service and Food and Drug Administration of the 
United States Department of Agriculture (USDA), and United States Department of Health 
and Human Services. The FDA and FSIS are the Food Safety Working Group that share 
authority for helping to ensure the safety of America food supply. Each agency investigates 
foodborne illness outbreaks and other foodborne risks (including drug residues) associated 
with the products they regulate. These investigations, conducted in close cooperation with the 
U.S. Centers of Disease Control and Prevention and state and local health and agriculture 
Departments, often involve tracing backward or forward in the supply chain the distribution 
of food products and ingredients associated with risk to consumer health (FDA-FSIS, 2009). 
FSIS release monthly list of individuals or firms responsible for repeat drug, pesticide, or 
other chemical residue violations in animals presented for slaughter. 
2.2.7.1 Acceptable daily intake (ADI) 
The ADI is an estimate of the residue, expressed on a body weight basis that can be ingested 
daily over a lifetime without any appreciable health risk (EC, 2001). The ADI approach was 
originally developed to take account of effects based on classical toxicology, and it was 
applied to the results of standard toxicity studies. These studies were used to derive a 
NOAEL. The ADI was calculated by dividing this by a suitable safety factor, usually 100, 
which assumes that humans are 10 times more sensitive than animals and that within the 
human population there is a 10-fold range of sensitivity (IPSC, 1987; Woodward, 1998). 
Standard toxicological studies are inadequate in evaluating adverse effects of antimicrobials, 
thus the determination on microbiological endpoints is necessary (Perrin-Guyomard et al., 
2001). Microbiological properties of residues are included in the safety evaluation at national 
and international levels (WHO, 1991; US FDA, 1996; CVMP, 2001a and 2001b). 
In the EU, the classical toxicology tests required include single dose toxicity, repeated dose 
toxicity, tolerance in the target species, reproductive toxicity, mutagenicity and 
carcinogenicity. Studies on other effects include immunotoxicity, microbiological properties 
of residues, observations in humans, and neurotoxicity (EC, 2001). In the determination of a 
microbiological ADI, various in vivo and in vitro methods have been developed for testing 
the effects of the drug residues on human intestinal microbiota.  Changes in microbiota can 
be measured by selectively culturing and identifying the predominant species by traditional 
bacteriological methods, by enumerating the enterobacteria as an indication of colonization 
resistance status, by measuring the biochemical activities of the bacterial enzymes in human 
fecal samples and by monitoring the susceptibility of the microbiota to colonization by a 
challenging organism. Studies in vitro, such as those to determine the MIC, are relatively 
simple to carry out and inexpensive, but are not always representative of the relevant bacteria, 
and may not take into account factors such as pH, anaerobiosis and the barrier effect 
(Boisseau, 1993; Cerniglia and Kotarski, 1999).  
The US FDA does not accept the use of in vitro MIC data for establishing a microbiological 
no-effect level. The human-microbiota-associated rodent model may have high relevance in 
determining the effects of low concentrations of antimicrobials on human microbiota 
(Boisseau, 1993). An in vitro gut simulation model (McConville et al., 1995) has also been 
considered as a good means for testing the effects. Studies in human volunteers enable the 
establishment of a no-effect level in conditions which most closely mimic the conditions of 
use. However, they are less favorable from a practical and ethical point of view (Boisseau, 
1993). According to US FDA, (1996) the model system used to establish the microbiological 
NOEL evaluates changes in metabolism of intestinal microbiota, the selection of 
antimicrobial resistant organisms, and/or changes in colonization resistance to potentially 
pathogenic microorganisms (Greenless, 2003).  
2.2.7.2 Maximum Residue Limit (MRL) 
According to Council Regulation 2377/90 (EEC, 1990) maximum residue limit is the 
maximum concentration of residue of both the parent drug and/or the metabolites resulting 
from the use of a veterinary medicinal product which may be legally permitted or recognized 
as acceptable in or on a food. It is based on the type and amount of residue considered to be 
without any toxicological hazard for human health as expressed by the ADI.  In calculating 
MRL and ADI, the residue depletion patterns of a compound in the edible tissues of a 
particular food-producing animal and the theoretical food intakes are taken into account. 
Possible persistence of residues in organs or at the injection sites is also considered 
(Fitzpatrick et al., 1995; EC, 2001). Once the process of safety evaluation is complete and 
MRLs have been derived for a particular substance, consideration is given to the likely level 
of residue which may be expected to remain after the use of the substance in accordance with 
good veterinary practice, and to the availability of analytical detection methods suitable for 
use for routine monitoring purposes. Internationally the MRLs and ADIs are developed and 
recommended as Codex MRLs (i.e. international standards) after the risk assessment has been 
performed by Joint FAO/WHO Expert Committee on Food Additives JECFA of the Codex 
Alimentarius Commission. The MRLs may be further reduced to take safety factors into 
account (EEC, 2001).   
2.2.7.3 Withdrawal period 
Following the use of a veterinary drug in food animals, a specified period of drug withdrawal 
is set to be observed prior to providing any products for human consumption. This period will 
ensure that the drug residues have declined to a safe concentration in the edible portions of 
the animals It is the time which passes between the last dose given to the animal and the time 
when the concentration of residues in the tissues: muscle, liver, kidney, skin/fat or products 
milk, eggs, honey is lower than or equal to the MRL (Jackson, 1980). The CVMP 
recommends the use of a statistical method in the assessment of a withdrawal period (CVMP, 
1995) whenever possible, and particularly for products containing new chemical entities. 
Linear regression technique is recommended. A withdrawal period is determined at the time 
when the upper one-sided tolerance limit with a given confidence when the residues in all 
tissues of all observed animals have fallen below the respective MRLs (Concordet and 
Toutain, 1997). Failure to adhere to these recommended periods is reported to be the primary 
cause of violative levels of veterinary drugs in food (Kabir et. al., 2004; Kukanich et al., 
2005). The maximum residue limit for veterinary drugs (MRLVD) can be assured with good 
practice in the use of veterinary drugs which implies the official recommended or authorized 
usage including withdrawal periods, approved by national authorities, of veterinary drugs 
under practical conditions. 
2.2.8 Detection and Analysis of Antimicrobial Residues 
The effectiveness and accuracy of the residue monitoring and surveillance program depend 
on the proper choice of the antibiotic screening and analytical tests. These tests designed for 
use by regulators and producers are used for the detection of antibiotic contamination in food 
to reduce or prevent the introduction of contaminated meat and milk into food chain (Popelka 
et al., 2005). Since residues are present in very low levels in foods very sensitive methods are 
used for their detection, also due to the diversity of their chemical structures, the methods of 
choice are expected to be discriminatory i.e. sensitive and specific. In recent time the 
methods for detection and characterisation of chemical and veterinary drug residues in foods 
of animal origin has been a dynamic area in food processing and is experiencing important 
developments mainly from the standpoint of food safety undergoing (Toldra and Reig, 2006). 
Different nationals and food safety regulators are developing and adopting varieties of 
techniques; however, CAC reviews and recommends both the qualitative and quantitative 
approaches for international equivalence in food trade.  
Several methods have been developed for the detection and quantitative analysis of drugs 
residues in animal tissues (Crosby, 1991). The analysis of antibiotic residues in animal tissues 
is generally grouped into qualitative (screening) and quantitative (confirmatory or physico-
chemical) methods. The methods involved include microbiological assay, immunoassays and 
several forms of chromatographic analysis such as thin - layer chromatography (TLC), high 
performance TLC, gas - liquid chromatography (GLC) and high performance liquid 
chromatography (HPLC) (Okerman et al., 1998a). An essential tool in assuring the safety of 
food products is the availability of a simple and reliable screening system for the detection of 
antibiotics (Popelka et al., 2005). Regulatory monitoring programmes involve analysis of 
large samples which may be prohibitive in term of cost (Fletouris et al., 1990). Hence the 
common approach is the use cheap, sensitive, simple and rapid screening procedure initially 
to reduce numbers of samples to the suspected cases which are further confirmed by chemical 
methods. Thus a screening method is the first-hand analysis of the sample to establish the 
presence or absence of residues (Aerts et al., 1995).  Screening tests allow a large number of 
samples to be analyzed in relatively short time, and are designed to minimize the number of 
false negatives. When a positive sample is found by a screening test, a confirmatory test is 
carried out, which normally involves a more sophisticated testing method that provides full or 
complementary information, enabling the substance to be identified precisely (Popleka, 
2005). 
2.2.8.1 Screening Methods 
2.2.8.1.1 Microbiological Assay 
The traditional methods of residue analysis in animal tissues, eggs and milk have been 
microbiological procedures. An appropriate microbiological method should be a low-cost and 
high-sample throughput method, optimised to prevent false-negative results and to have an 
acceptable number of false-positive results (Heitzman, 1994; Korsrud, and MacNeil, 1987). 
Microbiological assays depend on the ability of antibiotics to inhibit the growth of sensitive 
bacterial test organisms. This growth inhibition can either be manifested as failure to form 
colonies whereby a clear zone of inhibition is observed, or by the suppression of the 
organism's normal metabolic processes which results in the production of acid or gas 
(Crosby, 1991). Traditionally the methods require overnight incubation and are considered as 
multi-residue screening tests for antibiotics in milk, meat and other animal tissues. The size 
of the inhibition zone is determined by the interaction between the growth of the test 
organism and the diffusion of the antibiotic from its point of application in the test agar 
(Crosby, 1991). Methods based on inhibition are useful for the detection of an antibiotic or a 
group of antibiotics. For these tests, the micro-organism Bacillus spp. is often used. However, 
inhibition tests may be of high sensitivity but they lack specificity. They cannot distinguish 
among different forms antibiotics, therefore every inhibition test can only be used as a tool 
for screening. Some of the microbiological methods may be very time-consuming as they 
may require 24 hours incubation. Several microbiological assays have been described for the 
detection of antibiotic residues in meat.  
(i) The four-plate test (FPT) 
The FPT was described in the Manual of Reference Materials and Methods to Detect 
Veterinary Drug Residues (Heitzman, 1994), originally, the FPT was developed to identify 
five different groups of antibiotics: beta-lactam antibiotics, tetracyclines, sulphonamides, 
aminoglycosides and macrolides. The method does not detect sulphonamides, and is not 
reliable for detection of aminoglycosides or macrolides in meat (Okerman et al., 1998b).  The 
method involves incubation of thin slices of meat on agar plate inoculated with Bacillus 
subtilis spores at pH values 6, 7.2, and 8, together with a further plate inoculated with 
Micrococcus luteus at pH 8. The formation of annular zones of inhibition of at least 2mm 
wide to one or both microorganisms indicates the presence of an antibacterial substance. The 
FPT is based on the inhibition of growth of the micro-organism, which is included in the test. 
This inhibition becomes visible as a clear zone around the sample; in the case antibiotic 
substances are present at or above the limit of detection (LOD) of the plate. The size of this 
zone is dependent on the antibiotic concentration present in the meat sample. 
(ii) The swab test on premises (STOP)  
STOP is another microbiological method of detecting antimicrobial residues developed in the 
USA. This assay was specifically designed to be used by non-specialist inspectors at the 
slaughterhouses for the routine Control Of antibiotic residues in meat. In this method, slits are 
cut into the carcass and sterile cotton swabs are inserted for 30 minutes to soak up the 
exudate. The swabs are then laid on prepared agar plates seeded with Bacillus subtilis and 
O
incubated overnight at 29 C, after which the plate is observed for inhibition zones. 
Microbiological methods are suitable for large scale screening because of their convenience 
and broad spectrum characteristics (Aerts, 1995). In the search for rapid methods for 
determining the interaction of antimicrobial agents and organisms, intermediate and end 
products of bacterial metabolism, as well as the interaction of the organism with various 
energy sources have been examined (Amsterdam, 1996). Currently, most microbiological 
methods used in antimicrobial residue analysis are based on agar diffusion, which have been 
developed to rapid screening kits. 
2.2.8.1.2 Immunological Techniques 
Antigen and antibody reaction has been used for many years to detect a wide variety of food 
constituents including substances responsible for adulterations and contaminations. The basis 
of immunoassays is an interaction between an antibody and a corresponding antigen, and the 
detection of the interaction. In the immunoassay analysis of antibiotic residues in meat, the 
antigen is the antibiotic, but because most of the antibiotics have low molecular weights, they 
are by themselves not immunogenic, and have to be coupled with another molecule to form 
hapten, which are then rendered immunogenic by the attachment of a large macromolecular 
substance such as albumin (Heitzman, 1994). The detection of the antibody-antigen 
interaction is facilitated by the use of labels. These labels, which can either be attached to the 
antigen or the antibody may be radioactive atom in radio immunoassay (RIA), an enzyme in 
enzyme immunoassay (EIA) or a fluorescent substance in fluorescence immunoassay (FIA) 
(Heitzman, 1994). The interaction antigen–antibody is very specific and useful for the 
detection of residues of chemical and veterinary drugs in animal foods. They are relatively 
easy to perform and capable of detecting very low levels of residues even if the residues are 
covalently bound to proteins. However, their application is limited by the availability of 
suitable antibodies. In addition, immunoassays frequently lack specificity, since any 
compound, part of which is identical with or closely similar to the antigenic determinant of 
the analyte can compete for antibody binding sites. The most usual technique consists in the 
enzyme-linked-immunosorbent assay (ELISA) and the detection system is usually based on 
enzyme-labelled reagents. ELISA kits have been developed, they showed good performance 
for analysing antibiotic residues like tylosin and tetracycline in meat (Draisci et al., 2001), 
chloramphenicol in milk and meat (Gaudin et al., 2004). Delwiche et al., (2000) developed 
an enzyme immunoassay to detect penicillin residues in meat and dairy products. 
Radioimmunoassay (RIA) is another technique which involves measurement of radioactivity 
of immunological complex using a counter (Delwiche et al., 1991). A preliminary 
purification step is often necessary whereas some require the use of bio-hazardous radioactive 
isotopes which have a relatively short shelf life (Katz, 1982). 
2.2.8.1.3 Antibiotics Residues Rapid Screening Kits 
Several commercially immunological (Charm II test) or ELISA and microbial inhibition 
®
(Delvotest SP and Premi Test) test kits have been developed for rapid screening and 
detection of antibiotics residues in food.  
 
 
(i) Charm II Test  
The Charm II test produced by Charm Sciences Inc., USA is a screening test, used in 
different food items such as meat, milk and testing. It is based on the specific binding of 
3 
antibiotics to receptors. The quantitation is determined by measuring of radioactivity: H r C. 
The test has been shown to detect the several groups of antibiotics in food sulfonamides, 
tetracyclines, beta-lactams, macrolides, amphenicols and aminoglycosides of the 
streptomycin type. The screening by the Charm test will exclude the negative samples with 
low rate of false positive results (Edder and Corvi, 2001). 
(ii) Premitest 
®
Premi test (DSM food industries, Netherlands), is commercially available in kit form and has 
been shown to be responsive to wide variety of antibiotics (Stead et al., 2004). It provides a 
simple yes/no response to presence of antibiotics using Bacillus stearothermophilus, a 
thermophilic bacteria, which is responsive to all of the most commonly used antibiotics and 
provides a measurable effect when exposed to samples of contaminated meat or other 
®
substrates (Reybroeck 2000). The Premi Test is based on the inhibition of growth of Bacillus 
stearothermophilus, a thermophilic bacterium sensitive to many antibiotics (Stead et al., 
2004). The microbiological inhibition by this kit is obtained within 3hours and has been 
validated to detect residues of some antibiotics below MRLs (Popleka et al., 2005). 
®
Premi Test is simple, cheap, and practical in routine residue testing. The great advantage of 
® ®
the Premi Test is the short time of the analysis within 4 hours. Premi Test involves simple 
equipments and techniques that can relief the chemical analytical resources of food inspection 
laboratories (Popleka, 2005). 
 
2.2.8.2 Physico-chemical (Quantitative) Residue Analysis Methods 
According  to  the  Codex  Guidelines  for  the  Establishment  of  a  Regulatory Programme 
for Control of Veterinary Drug Residues (CCFH, 1993), methods that are suitable for 
determining compliance with MRLs are those that have successfully completed  an  
extensive,  multi-laboratory  study  for  specific  tissue  and  species combination. In some 
cases, these methods may be considered reference methods. Chromatographic methods are 
commonly employed in the confirmatory quantitative analysis of drugs and pesticides 
residues in different food and tissue matrices. 
2.2.8.2.1 Chromatographic Techniques 
Chromatography is a common name for techniques based on the partition of the molecules to 
be analyzed between a mobile and a stationary phase. Separation is the result of different 
partitions of molecules between the two phases. Because of the high sensitivity, selectivity, 
and reproducibility of chromatographic methods have been extensively exploited in food and 
nutrition science and technology (De Wasch et al., 1998). Chromatography is a method of 
analysis in which the flow of solvent or gas promotes the separation of substances by 
differential migration from a narrow initial zone in a porous sorptive medium. 
Chromatography method enables the qualitative and quantitative analysis of residues of 
pharmacologically active substances in food products of animal origin.  Chromatographic 
techniques include high performance liquid chromatography (HPLC), gas chromatography 
(GC) and thin layer chromatography (TLC). Thin layer chromatography are useful for 
handling many samples simultaneously and may greatly assist in residue identification 
through the use of derivatizing reagents specific for each functional group but  precision 
cannot be compared with that of gas chromatography or high performance liquid 
chromatography  (Aerts et al., 1995; McCracken et al., 2000). 
Gas chromatography (GC) is the common name for chromatographic methods in which the 
mobile phase is gas, and the stationary phase is solid or liquid (gas– solid chromatography 
(GSC) or gas–liquid chromatography (GLC)). A compound needs to have an appreciable 
o
vapour pressure at temperatures below 350–400 C and has to be vaporized rapidly without 
decomposing or reacting with the components of the stationary and mobile phase. Gas 
chromatographic technique has very limited application to the determination of antibiotic 
residues in animal tissues (Shaikh and Moats, 1993; Botsoglou and Fletouris 2001) because 
most antimicrobial agents are non-volatile and will required to be made volatile by 
derivatization. Most antimicrobials are either insufficiently volatile and are thermally 
unstable to permit their analysis using GC (Oka et al., 2000).  Losses of residues can occur 
during derivatization.  Since residues occur at low concentrations, such losses may 
significantly affect the reliability of the analysis (Shaikh and Moats, 1993; Kennedy et al., 
1998).  
High performance liquid chromatography offers many advantages in residue analysis over 
other analytical methods (Botsoglou and Fletouris 2001). It is a very useful technique for the 
separation of compounds which are not easily separable by other means and gives the best 
separation efficiency (Oka et al., 2000). High performance liquid chromatography (HPLC) 
has been applied successfully for the qualitative and quantitative detection of multi-residues 
in food samples. HPLC is getting expanded use in control laboratories due to the possibility 
to analyse simultaneously multiple residues in a sample in relatively short time and is 
increasingly used in the field of residue analysis. The popularity of the method is largely due 
to the variety of mobile phases, the extensive library of column packing, and the variation in 
modes of operation e.g. normal - phases (partition) ion exchange. Recent developments of 
high speed HPLC can reduce sample treatment and analysis time. In addition, this technology 
is fully automated (injection, elution, washing of column, detection) and computer-controlled, 
facilitating its use as a screening technique.  The basic isocratic high performance liquid 
chromatography can be considered to consist of an injection loop, high-pressure pulse – 
pump, column with appropriate packing and a detector. A typical HPLC analytical scheme 
involves sample preparations (extraction and clean-up), chromatographic separation (elution), 
resolution and detection. 
(i) Sample Preparation  
Sample pre-treatment before chromatographic separation involve extraction and clean-up. In 
the analysis of residues from edible animal products, the sample often has a very low content 
of the residues but much higher concentration of endogenous interfering components. 
Physico-chemical methods usually proceed with a preliminary extraction in order to isolate 
the drugs of interest from the biological matrix. The main objectives of sample treatment are 
removal of macromolecules and other matrix constituents that may either adversely affect the 
chromatographic system or interfere with the detection, and enrichment of the analytes in 
order to achieve the required low limits of detection (Aerts et al., 1995).  
(a) Extraction 
According to Botsoglou and Fletouris (2001), the first step in residue analysis of food of 
animal origin is sample deproteinization. This may be accomplished by the addition of 
mineral or organic acids such as hypochloric or trichloroacetic acid and/or water-miscible 
organic solvents such as acetonitrile, acetone or methanol which precipitate the protein to 
allow their removal by centrifugation. Organic solvents such as dichloromethane or 
chloroform, although less efficient precipitants can be used but much higher volumes are 
required. Sample deproteinization not only protects the HPLC column from irreversible 
contamination, but may also be effective in releasing protein bound residues (Shaikh and 
Moats, 1993).  Extraction efficiency is generally determined by the polarity of the extracting 
solvent, the PH of the sample/solvent system, the sample to solvent volume ratio and the 
method of contacting sample and solvent. 
 (b) Clean-up 
The extract obtained from the extraction process most often contains too much co-extractive, 
which might interfere with antibiotic detection. This necessitates the need for sample clean-
up. Clean-up refers to the separation of the analyte from co-extracted matrix constituents. 
Several methods are used for this process; the easiest method is the liquid-liquid partitioning 
between immiscible solvents allowing the analyte to be selectively partitioned in one of the 
two phases and most of the interfering components in the other phase. In this method the 
extract and an immiscible solvent are manually or mechanically shaken and allowed to 
separate in a funnel. Organic solvents are usually used as extracting agents, they are better 
than water because of their power to denature proteins which permits not only the extraction 
of free residues but also of non-covalently bound residues (Botsoglou and Fletouris (2001). 
Solid phase extraction SPE also known as liquid/solid extraction method involves the use of a 
solid surface (usually based on a powdered silica to which organic functional groups have 
been bonded) as the extracting phase, on which the compounds to be extracted can be 
retained. The type of SPE to be used is chosen based on the nature of the compounds and the 
solution from which the compound is extracted. This clean-up method is rapid and requires 
lesser amount of solvents than Liquid-solid extraction or solid phase extraction (SPE) 
procedures on the other hand, offer an important alternative to solvent partition to eliminate 
problems associated with the separation of the two liquid phases (Oka et al., 2000). 
Disposable SPE columns or cartridges containing a wide range of adsorbent including silica, 
alkyl-bonded silica or ion exchange materials are commercially available. 
 
(ii) Chromatographic separation 
HPLC analysis of antimicrobial residues can be performed in either the normal or reverse-
phase mode, and in the ion - exchange mode. The choice is governed by the polarity and the 
ionisable groups of the analytes. However, simultaneous separation of both ionised and non-
ionized compounds cannot be carried out. In the reverse-phase HPLC, many parameters can 
influence both the resolution of the compounds and column efficiency (Botsoglou and 
Fletouris (2001). A combination of the appropriate stationary/mobile phase system and mode 
of elution (isocratic or gradient) help to obtain best results. 
(iii) Resolution and Detection 
After the clean-up process, the purified extract is analysed by a suitable chromatographic 
method in order to detect, identify and to measure quantitatively the analyte. Most 
antimicrobials have relatively high molar absorbtivity within the UV absorption range, such 
that UV detection permits quantitation to be made with high sensitivity. Single/variable 
wavelength UV detectors or UV with spectrophotometers equipped with stop-flow scanning 
capabilities and photodiode array UV spectrophotometers have all been widely used for 
quantitative purposes. Antimicrobials that strongly fluoresce can be detected by fluorescence 
spectroscopy. The elute compounds are usually identified by comparing their retention time 
with those of reference analytical standards processed in an identical manner. 
2.9 Antimicrobials use in Livestock  
Veterinary use of antibiotics started soon after it became available for the treatment of human 
diseases in mid 1940s. Penicillin was used to treat mastitis before World War II. In food 
animals, antimicrobials are used for the control (prophylaxis) and treatment (therapeutic) of 
bacterial associated infectious diseases as well as for growth promotion purposes (Phillips et 
al., 2004). The use of drug in food animals are supposed to the principle of Good Veterinary 
Practice (Nouws, 1990). In relation to pharmacotherapy GVP is defined as; The selective use 
(in accordance with directions for users) of veterinary drugs registered by the authorities in 
those indications in which they are permitted when the diagnosis has been established and in 
which the problem of residues in foods of animal origin on using these agents has been taken 
into account (van Miert, 1990). Farmers and veterinarians have a key role to play in the 
avoidance of residues by ensuring safe and prudent use of veterinary medicines such as the 
need to follow label instructions and observe withdrawal periods. 
The accurate figures on the antibiotic use in humans or animals are usually difficult to obtain 
since the use are affected by various socio-cultural, economic and political factors (Okeke et 
al., 2007). Antimicrobials represent the largest proportion of pharmaceutical sales both in 
volume and money value of any drugs used in animal production (Kaneene and Miller, 1997).  
It has been estimated that as much as 50% of total antibiotic production (by weight) is used in 
animals and plants, with 50–80% used in some countries for growth promotion or disease 
prophylaxis and the rest used for therapeutic purposes (WHO, 2000). In the United States 
alone some 15 million pounds of antibiotics are administered to farm animals annually 
(Walter, 2005), while Mellon, et al., (2001), estimated annual use of antibiotics by livestock 
producers in the United States as 12.5 million kilograms of antimicrobials for non-therapeutic 
purposes. Most data on antimicrobial use in humans and animals are based on the monetary 
value of sales of antibiotics per annum (Kaneene and Miller, 1997). However, antibiotic use 
in humans is more expensive per gram of active compound than therapeutic and growth 
promoter antibiotic use in veterinary medicine and animal husbandry (Gustafon and Bowen, 
1997; van den Bogaard and Strobberingh, 1999). They concluded that consumption of 
antibiotics by animals might be higher, because the lifespan of food animals is short 
(approximately 7 weeks for broilers, and 6 months for fattening pigs). More so, that the 
dosage per kg bodyweight in small animals like poultry, is much higher than that in humans. 
Prescott (1997) and Levy (1998) also estimated about 55 to 60% of benzylpenicillin 
(penicillin G) and tetracyclines used in US were used in food animal feeds mainly at 
subtherapeutic doses mixed in animal feeds. In the EU and Switzerland in 1997, 10493 tons 
of antibiotics (active ingredient at 100% purity) were used and of this amount nearly 50% 
was used in animals where 3474 tons (33%) were used in animals for therapy and prevention, 
and 1590 tons (15%) as growth promoters. According to the European Federation of Animal 
Health Industries (FEDESA), the World Animal Health Product Market was, at 
manufacturers‟ prices, 11 billion Euros in 1995, of which 44%were therapeutic 
pharmaceutical products and 41% feed additives (EU, 2002).  
2.9.1 Antibiotics as Growth Promoters 
Antibiotics are used in food animals both therapeutically to treat disease and 
subtherapeutically, usually over long periods, to improve their rate of growth and feed 
conversion efficiency. The mechanisms responsible for growth promotion have not been fully 
elucidated but appear to include enhancement of vitamin production by gastrointestinal 
microorganisms, elimination of subclinical populations of pathogenic organisms, and 
increased intestinal absorption of nutrients (Committee on Drug Use in Food Animals, 1999). 
The use of antibiotics as feed additives especially in broilers and fatteners has been shown to 
improved growth performance and improve feed efficiency 17% in beef cattle, 10% in lambs, 
15% in poultry and 15% in swine (Nisha, 2008). They may produce improved growth rate by 
the thinning of mucous membrane of the gut, facilitating better absorption, altering gut 
motility to enhance better assimilation, producing favourable conditions to beneficial 
microbes in the gut of animal by destroying harmful bacteria and partitioning proteins to 
muscle accretion by suppressing monokines. Antibiotics also favour growth by decreasing 
degree of activity of the immune system, reduced waste of nutrients and reduce toxin 
formation. Indiscriminating use of antibiotics in all cases of pyrexia, inflammation, wounds 
and viral diseases have widespread residual effects on edible tissues (Nisha, 2008).  
Most livestock producers indiscriminately feed antibiotics to healthy farm animals to promote 
growth and compensate for unhygienic husbandry. Van den Bogaard, (1998) concluded that 
the selection pressure exerted by the veterinary use of antibiotics on the animal bacterial 
population selection pressure could be more than doubled in intensively reared animals than 
by human use due to their use as growth promoters along with prophylactic and therapeutic 
uses. The use of antimicrobial growth promoters in particular, has being receiving global 
attention and scrutiny as most antibiotics used in animals are also used in human medicine.  
The use of antimicrobial growth promoters have direct association with the resistance 
observed in indicator bacteria isolated from livestock animals (Bates et al., 1994; van den 
Bogaard and Stobberingh, 2000; Swartz, 2002). These have led to regulatory precautionary 
measures taken against the use of certain antimicrobial agents (Swartz, 2002). In the 
European Union, the only four agents are acceptable for use as AMGP are monensin-Na, 
salinomycin-Na, flavophospolipol, and avilamycin (Butaye, 2000). These antimicrobial 
agents are considered unlikely to exhibit cross-resistance with therapeutic compounds used in 
human and veterinary medicine (Schwarz et al., 2001). 
2.9.2 Antimicrobials Use in Animal and Resistant Bacteria Transfer to Man  
There is a casual relationship between increased use of antibiotics and increased prevalence 
of resistant bacteria has been demonstrated (Holmberg et al., 1987). The question of whether 
antibiotic use and antibiotic-resistant isolates of bacteria from animals have an impact on 
human health has been under scrutiny since the Swann (1969) report was published. WHO 
has recognized the global public health threat of increasing antimicrobial resistance as 
ominous and reported that the window of opportunity for the control and elimination many of 
the infectious diseases, including those caused by antibiotic resistant bacteria is closing 
(WHO, 2000). It is generally accepted that antimicrobial resistance in veterinary medicine 
could form a potential public health hazard. Indeed, the commensal gastrointestinal flora 
(indicator bacteria) of healthy animals harbour reservoir of resistance genes that are 
transferable to human being through the food chain or by direct contact (van den Bogaard and 
Stobberingh, 1999). This is more important because livestock are carriers of food-borne 
pathogens such as Salmonella and Campylobacter species that constitute zoonotic pathogens 
undergoing selection pressure due to the use of antimicrobial drugs resulting in clonal and 
horizontal transfer of resistance genes. These are transferable to humans through the food 
chain and/or through direct contact during processing (Kruse et al., 1998).  
The wide spread use of antibiotic in human and animals has been followed by the increased 
emergence of bacteria resistance to these antibiotics, particularly in enterobacteriaceae 
(Prescott and Baggot, 1993). Most concern about antibiotic resistance in animal isolates of 
bacteria is directed towards the enteric bacteria, E. coli, Salmonella, thermophilic 
Campylobacter and enterococci. There is considerable information on antibiotic resistance in 
E. coli and Salmonella, as these bacteria are recognised pathogens in animals, but there is 
relatively little information about antibiotic resistance in thermophilic campylobacters and 
enterococci, as they are regarded as commensal enteric organisms rather than animal 
pathogens. Antibiotic resistance was detected in isolates of E. coli from animals soon after 
antibiotics were incorporated into animal feeds (Smith 1967). Studies in the UK found that, in 
the late 1950s, tetracycline resistance was already detectable in E. coli isolates from chickens 
and pigs fed rations containing less than 100 g tetracycline/ton (Smith, 1967). Resistance to 
other antibiotics was detected as new agents were introduced for therapeutic and growth-
promotant purposes (Smith, 1967; Anderson, 1968). Some workers (Linton et al., 1985; Lee 
et al., 1993) also noted the occurrence of tetracycline resistance in some piggeries, even 
though tetracyclines had not been used in those piggeries. A common finding has been that 
resistance persists after antibiotics are withdrawn (Smith, 1973; Hinton et al., 1985). Feeding 
oxytetracycline to recently-weaned pigs was found to lead to a rapid increase in the incidence 
of tetracycline resistance, which was widely distributed among all strains of E. coli present, 
rather than being restricted to a few selected clones (Hinton et al., 1985). The feeding of low 
doses of ampicillin to chickens was shown to select for high levels of resistance to that 
antibiotic (El-Sam et al., 1993). Marshall et al., (1990) described an elegant experiment that 
demonstrated that resistant strains of E. coli spread among animals (and to other species such 
as mice), even in the absence of ongoing antibiotic treatment.  It is clear that resistance to 
antibiotics has become very common in E. coli over the 50 years of use of in-feed antibiotics 
(Aalback et al., 1991; Adesiyun and Kaminjolo, 1992; Nijsten et al., 1993; Dunlop et al., 
1998a; Orden et al., 1999; Lambie et al., 2000). Widespread resistance was seen in herds and 
flocks treated with tetracycline, aminoglycoside and sulphonamide, (Dunlop et al., 1998a; 
Sunde et al., 2006). However, resistance to other antibiotics such as ampicillin and 
olaquindox was less widespread (Linton et al., 1988; Dunlop et al., 1998).  Resistance to 
fluoroquinolones have also been reported (Blanco et al., 1997). Resistance to more than one 
class of antibiotics was the rule rather than the exception in these published studies. 
Antibiotic resistance in salmonella was also reported soon after antibiotics began to be fed at 
subtherapeutic levels to animals (Anderson, 1968). As salmonella is a recognised food-borne 
pathogen, a number of the published reports of resistance patterns in animal isolates have 
been linked with studies of human isolates (Threlfall et al., 2000; Seyfarth et al., 1997). Some 
countries have carried out surveys of resistance in animal isolates of salmonella or have 
ongoing antibiotic-resistance surveillance programmes (Wray et al., 1996; Seyfarth et al., 
1997; Davis et al., 1999). The results were not easy to interpret because some reports do not 
distinguish between different serovars of Salmonella enterica and it is recognised that some 
serovars such as Typhimurium are much more likely to be resistant than other serovars. 
Resistance to apramycin was reported in both E. coli and Salmonella within 3 years of its 
licensing for use in the UK (Wray et al., 1997) and fluoroquinolone resistance within a few 
years of enrofloxacin first being used (Griggs et al., 1996).  
There are few reports on antibiotic resistance Thermophilic Campylobacters which are 
mostly commensal enteric commensal of farm animals. Moore et al., (1999) reported 
resistance Campylobacter coli isolates. Aarestrup et al., (1997) found that tetracycline 
resistance was more common in human isolates than in pig or poultry isolates, and that there 
was more macrolide and streptomycin resistance in isolates from pigs than in human and 
poultry isolates. Resistance to ampicillin, spectinomycin, streptomycin, sulphonamides and 
nalidixic acid (but not fluoroquinolones) was detected in campylobacter isolates in Ireland 
(Lucey et al., 2000), whereas a study in Spain (Saenz et al., 2004) reported very high levels 
of ciprofloxacin resistance in pig and poultry isolates. In addition, there were high levels of 
resistance to erythromycin, ampicillin, gentamicin and amikacin in pig isolates and high 
levels of ampicillin and gentamicin resistance in poultry isolates. The difference between 
these two studies presumably reflects differences in antibiotic usage in the two countries. 
According to Witte, (1998) antibiotic resistance is a complex ecological phenomenon, 
resistant genes and bacteria can be transmitted in several ways such as via food, water, 
occupational exposure by farmers, hospital workers butchers and food processors.  Also the 
local water ways and ground water get contaminated with these bacteria via animal manure 
used in agriculture (figure 2.2).  
 
Figure 2.3: Ecological relationships between antibiotic-resistant bacteria and resistance        
genes: selective pressures, main reservoirs, and routes of transmission (Witte, 1998) 
 
 
 
 
 
 
 
 
 
 
2.9.3 Regulatory Control of Veterinary Drugs Use and Residues in Food Animals 
Food safety and quality have become increasingly important world-wide in recent years, not 
only in terms of protecting the health of the consumers, but also to meet requirements for 
international trade. Application of necessary analytical capacity to detect and monitor food 
contaminants such as pesticides and veterinary drugs during the production process and in 
finished food products is critical to assurance of chemical safety of the agricultural products 
(SOFA, 2009). The ability to demonstrate the origin and the authenticity of food products is 
also a major concern to food safety regulators and to trading partners due to increasing 
mobility and cross-border transportation of food commodities. Modern food production 
systems are supposed to be designed and managed to ensure that the exposure of food 
producing animals to veterinary drugs does not pose a risk to human health. Veterinary drugs 
are regulated in many countries for a variety of reasons, such as animal health, consumer 
protection, animal welfare and protection of the environment (CAC, 2009). Competent 
authorities responsible for providing consumer assurances of food safety and are supposed to 
ensure that it has sufficient knowledge of and control over veterinary drugs that are being 
sold and used within the production systems and have sufficient knowledge of food safety 
(CAC, 2009). 
2.10 FAO/WHO Residue Control and World Trade Organisation (WTO) 
The control of residues of veterinary drugs in animal products intended for human 
consumption is a question related to human health which falls as such under the purview of 
the Agreement of Sanitary and Phytosanitary Measures (SPS). The agreement stipulates that 
any SPS measure applied by a government to protect should conform to general WTO and 
more specific SPS rules if it affects products traded between two WTO members. The 
relevant definition of scope of SPS measure “human and animal life or health from risks from 
food additives, contaminants, toxins, disease causing organisms in foods, beverages or 
feedstuffs” includes also measures that address residues of veterinary drugs (SPS 
Agreement). Such measures may be laid down in laws, decrees, regulations, requirements or 
procedures related to the various actions that control or affect the putting into circulation of a 
product. Among the measures listed by the SPS agreement some of the following may be 
relevant to the question to be studied: end product criteria, production methods, testing, 
approval procedures, sampling procedures or risk assessment. The SPS Agreement explicitly 
recognizes the Codex Alimentarius and therewith the work of the Codex Alimentarius 
Commission which means that a country implementing a Codex standards fulfils the 
obligation resulting from its membership in WTO and with the relevant provisions of the SPS 
Agreement.  
2.10.1 Codex Alimentarius Commission (CAC) 
At the beginning of the 1960s the FAO Conference and the World Health Assembly decided 
to launch a joint effort in the area of food which should protect the health of the consumers 
and ensure fair practices in the food trade. This activity was and continues to be called the 
Joint FAO/WHO Food Standards Programme. The Codex Alimentarius Commission (from 
Latin words „Food Code‟), a subsidiary organ of FAO and WHO, develops the 
internationally-recognised food safety standards including veterinary drugs and pesticide 
residues in food. The CAC was jointly established by FAO and WHO in 1963 to promote fair 
trade while considering the global economic and personal health of the consumer.  Currently, 
there are 175 member countries subscribing to the international standards, codes of practice 
and guidelines to facilitate international trade of food products. CAC also provides 
information on innovative food safety systems, new technology and trade practices (Moulin 
and Lambert, 2008).  The Codex Alimentarius Commission has the objective of protecting 
the health of the consumers and ensuring fair practices in the food trade by developing food 
standards and other texts related to food safety and quality. With respect to veterinary drugs 
residues, the Commission recognized that “the occurrence and safety of residues of veterinary 
drugs in foods of animal origin was of significance to public health and consumer concern”. 
In 1985 it established the Codex Committee on Residues of Veterinary Drugs in Foods 
(CCRVDF), which was tasked to: 
 determine priorities for the consideration of residues of veterinary drugs in
 foods; 
 recommend maximum limits of such substances; 
 develop codes of practice as may be required; 
 consider methods of sampling and analysis for the determination of veterinary
 drug residues in foods. 
The Codex Committee on Residues of Veterinary Drugs determines priorities for the 
consideration of residues of veterinary drugs in foods and recommends Maximum Residue 
Limits (MRLs) for veterinary drugs. A Codex Maximum Limit for Residues of Veterinary 
Drugs (MRLVD) is the maximum concentration or residue resulting from the use of a 
veterinary drug (expressed in mg/kg or µg/kg on a fresh weight basis) that is recommended 
by the Codex Alimentarius Commission to be legally permitted or recognized as acceptable 
in or on a food.  An MRLVD is based on the type and amount of residue considered to be 
without any toxicological hazard for human health as expressed by the Acceptable Daily 
Intake (ADI), or on the basis of a temporary ADI that utilizes an additional safety factor. An 
MRLVD also takes into account other relevant public health risks as well as food 
technological aspects.  
MRLs and ADIs are developed and adopted as Codex MRLs (i.e. international standards) 
after the risk assessment has been performed by Joint FAO/WHO Expert Committee on Food 
Additives (JECFA). The recommended MRLs are achievable under Good Practice in the Use 
of Veterinary Drugs (GPVD) and a suitable analytical method is available. The evaluation 
process depends on the commitment of a sponsor to provide the data and to submit a dossier. 
Over two decades Codex has adopted MRLs for residues of approximately 50 veterinary 
drugs. 
All Codex food standards and other documents that intend to provide a basis for any 
regulation along the food chain are based on the principle of sound scientific analysis and 
evidence, involving a thorough review of all relevant information, in order that the standards 
assure the quality and safety of the food supply. As described above WTO requires for SPS 
measures the use of internationally accepted risk assessment techniques which has led to 
some basic food safety definitions as shown below. The definitions adopted by the Codex 
Alimentarius Commission (CAC, 2006) were elaborated by the Codex Committee on 
Residues of Veterinary Drugs in Foods (CCRVDF).  The definitions were established and 
adopted by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) and have 
been modified by the Codex Committee on Residues of Veterinary Drugs in Foods). 
2.10.2 Control of antimicrobial use and residues in different countries 
Drug manufacturers, the regulatory agency, the veterinarians, the producers, and the 
producer‟s employees involved in administering the feed additive have collective 
responsibility for controlling unintended public health impacts of antibiotic use in food 
producing animals. The regulatory monitoring and control of antibiotics use, resistance and 
residue vary from country to country. In the UK and other EU countries, antibiotics are 
authorised as either veterinary medicinal products or zootechnical feed additives. Veterinary 
medicinal products and growth promoters are subject to assessment for safety, including 
residues (veterinary medicines) and the risk of emergence of antibiotic resistance, cross-
resistance to therapeutic antibiotics and selection for transferable resistance (Rutter, 1997). 
EU Member States monitor a set proportion of the total annual production of different food 
commodities of animal origin for residues, veterinary drugs are monitored for MRL 
compliance according to Council Directive 96/23/EC EC (1996). The EU has banned the use 
of avoparcin, tylosin, spiramycin, bacitracin and virginiamycin as animal growth-promoter 
(AGP) in all member states because they belonged to classes of anti-microbial drugs also 
used in human medicine and the use of hormonal growth promoter (HGPs) on cattle. The 
directive establishes the groups of substances to be controlled for each food commodity. 
National residue control program is carried out in accordance with both national and EU 
legislation. Meat inspection involves bacteriological examination and testing for 
antimicrobial residues if there is any reason to suspect that a carcass could contain 
antimicrobial residues (MAF, 2003). In the EU, maximum residues limits based on 
microbiological effects have been set for e.g. cephalexin, CTC, doxicycline, EF, 
erythromycin, florfenicol, gentamicin, kanamycin, lincomycin, marbofloxacin, nafcillin, 
novobiocin, oxytetracycline, pirlimycin, sarafloxacin, spiramycin and tetracycline (EMEA, 
2004). An ADI not based on microbiological effects has been set only for a few 
antimicrobials, e.g. for danofloxacin, difloxacin, dihydrostreptomycin, neomycin, 
streptomycin and tiamulin. MRLs for penicillins are based on immunological effects and on 
the sensitivity of bacteria used in the dairy industry. Because of the impossibility to find a 
threshold concentration for chloramphenicol in the induction of aplastic anaemia in humans, 
due among other things to a lack of results from residue and toxicity test studies, no ADI 
could be set, and chloramphenicol was entered in Annex IV of the Council Regulation 
2377/90 (EEC, 1990). Annex IV includes substances for which no maximum residue limit 
can be established because residues of these substances, at whatever limits in foodstuffs of 
animal origin constitute a hazard to the health of the consumer. So, their use is prohibited 
(forbidden) for production animals. Annex I of the regulation includes substances for which 
final MRLs have been established, and Annex II substances for which it is not necessary for 
the protection of public health to establish MRL values. Annex III includes substances with 
provisional MRLs. 
China has regulated the use of antibiotics in animal feeds since 1989 and only non-medical 
antibiotics such as monensin, salinomycin, destomycin, bacitracin, colistin, kitasamycin, 
enramycin and virginiamycin are permitted as feed additives. While Russia also restricts feed 
antibiotics to non-medical drugs; bacitracin, grizin, flavomycin and virginiamycin are 
registered for use in this way (Panin et al., 1997). 
Agricultural use of antibiotics in the USA and Canada is also strictly regulated. In USA, 
antibiotics for animal production are approved by the Food and Drug Administration (FDA) 
after rigorous evaluation for safety against major risk factors with respect to the animal, the 
consumer, and the environment and their use is regulated to avoid unintended consequences. 
There are three categories of use: as feed antibiotics; as over-the-counter drugs; as veterinary 
prescription drugs. Feed antibiotics include antibiotics used as growth promotants and those 
used for subtherapeutic (including prophylactic and some growth-promotant use) and 
therapeutic purposes (Prescott, 1997). But AGPs are still widely used in the United States, 
However, the Food Safety Enhancement Act of 2009 was recently passed in the US towards 
securing effective and meaningful food safety regulation. In addition the US House is already 
considering HR 1549 (Preservation of Antibiotics for Medical Treatment Act of 2009).  Feed 
antibiotics are licensed for specific uses such as for meat chickens or young pigs or calves or 
feedlot cattle. In the USA preregistration assessment specifically addresses human health 
issues relating to antibiotic resistance in enteric coliforms, salmonella excretion and increased 
resistance in salmonella, increased virulence and pathogenicity of bacteria, animal disease 
that is difficult to treat, and residues and risk of hypersensitivity in consumers (Sundlof et al., 
2000). In the USA, National Residue Monitoring and Surveillance Program of FSIS conducts 
residue testing. Under the monitoring programme, statistically based selections of random 
samples from normal animal population is collected and monitor drug residues in their tissues 
(Sundlof et al., 2000).  
The Food Standards Australia New Zealand (FSANZ) protects the health and safety of people 
in Australia and New Zealand through the maintenance of a safe food supply and setting 
standards MRLs and ADIs (Brent, 2004).  There are three points of control of antibiotic use 
in animals in Australia. First, all importations are controlled by a permit system.  Second, at 
the registration level, there are strict regulatory guidelines over which antibiotics can be used 
in food-producing animals. Since 1970, antibiotics intended for animal use have been 
assessed for their potential to compromise human health. As a result, flouoroquinolones, 
amphenicols, colistin and gentamicin have not been registered for use in food-producing 
animals because of concerns about antibiotic resistance, and the registration of carbadox was 
withdrawn in the late 1980s and of nitrofurans in 1992 because of concerns about 
carcinogenicity (Joint Expert Technical Advisory Committee on Antibiotic Resistance, 
1999). 
2.10.3 Veterinary Drug Use and Control in Developing Countries 
There is a trend toward global increased consumption of meat, dairy and poultry products. It 
is estimated that the per capita consumption in developing countries of livestock products 
could rise by as much as 44% by 2030 (FAO, 2002). To meet this demand, commercial 
livestock production by intensive or semi-intensive peri-urban production systems rather than 
traditional mixed farming systems are being employed. There is a consequent increase in the 
use of pharmaco-active compounds such as antibiotics, coccidiostats and growth promoting 
feed additive to combat challenges of infections and enhance productivity. The use and 
control of veterinary drugs in developing countries vary between and within regions. 
Antibiotics are widely used in developing countries, due to the high incidence of infectious 
diseases in many areas and poor animal husbandry (Mitema et al., 2001; Al Mustafa and Al 
Ghamdi, 2002). Anthelmintics and trypanocides are also commonly used in of sub-Saharan 
Africa (Roderick et al., 2000). Many of the least developed countries lack the resources to 
assure food safety, and issues such as drug residues have a very low priority. However, as 
public awareness of food safety and quality issues grows, there is increased pressure on 
governments to address these issues even in low income countries. More so as member 
countries of World Trade Organisation (WTO), there are urge to participate in international 
livestock trade.  
In most developing countries there are no stringent regulatory legislation or mechanisms  on 
the use of veterinary drugs or for residues monitoring in food animals, thus occurrence of 
residues are usually expected (Cannavan, 2005). Veterinary drugs, including unapproved and 
unregulated compounds that may have no ADI, can often be easily purchased from village 
shops and informal vendors (Dina and Arowolo, 1991; Roderick 2000; Keyyu et al., 2003; 
Bett et al., 2004). There are no quality control of the substances supplied and concentrations 
and dosage rates may be incorrectly recorded (Bett et al., 2004). Antibiotics are also widely 
used in developing countries, due to the high incidence of infectious diseases in many areas 
and poor animal husbandry (Mitema et al., 2001; Al Mustafa and Al Ghamdi, 2002). 
However, the quantity used in this area is difficult to obtain due to lack of regulatory control 
of their uses. In developing countries livestock production are characterised by indiscriminate 
use of veterinary drugs and easy access to over the counter (Dina and Arowolo, 1991; 
Mitema et al., 2001).  There is often a lack of veterinary advice regarding withdrawal periods 
and this may be compounded by illiteracy, rendering labelling and printed instructions for 
drugs of limited use. Drugs are frequently administered by unqualified farmers or para-
veterinary field staff and extended usage or excessive or multiple dosages of the compounds 
are common. Treatment records are frequently poorly maintained or non-existent and 
individual animal identification and traceability is often impossible. For resource-poor 
farmers, a scarcity of meat and the fear of economic loss may prompt the slaughter of 
casualty animals for food (Cannavan, 2005).  
2.10.4 Drug Usage and Antibiotic Residues in Livestock Products in Nigeria 
Livestock diseases are major limiting factors affecting productivity and profitability through 
increase mortality and morbidity rates, reduced rates of reproduction, weight gain and milk 
production. Bacterial diseases are global livestock challenges and are recognised as a major 
risk factor in livestock production systems (Aibinu et al., 2007). Super-infections with 
bacterial agents also accompany other infections by viruses, protozoa and parasites. This 
engendered livestock farmers in the tropic spend more money on management and control of 
bacterial diseases. Disease constraints are estimated to cause losses of up to 30% of annual 
livestock output in developing countries, twice that estimated for developed countries (FAO, 
1990a). According to Blench and Marriage (1999), several factors affecting the distribution 
of livestock in Nigeria include the following broad headings; ecology, feed availability, 
diseases, animal traction marketing systems and cultural preferences including religion.  
These factors make the sector to be very complex for structural organisation and monitoring. 
In Nigeria like in many developing countries the livestock sector has not received appropriate 
commitments as it is not properly regulated and it is characterized by indiscriminate use of 
veterinary drugs including antibiotics which are easily obtainable over the counter without 
veterinary prescription and supervision (Dina and Arowolo, 1991; Dipeolu and Alonge, 
2002). Veterinary drugs including antibiotics are usually available for purchase in open 
markets over the counter without veterinary prescription and they are usually sold through 
channels of multiple middlemen mostly traders without knowledge of animal health 
management (Dina and Arowolo, 1991; Dipeolu and Alonge, 2002). There are several brands 
of veterinary drugs imported and sold in veterinary shops, livestock markets and drug 
peddlers directly to the farmers who use the drugs routinely without veterinary diagnosis or 
prescriptions (Dina and Arowolo, 1991). These encouraged the proliferation and use of 
substandard or fake drugs thereby increasing the rate of drug misuse and widespread 
resistance (Dina and Arowolo, 1991, Olatoye, 2010). The practice is also of great economic 
concerns as wastages result from avoidable drug usage, if proper expertise is involved in the 
husbandry and veterinary care (Ogundipe, 1997).  
The presence of antimicrobial residues in foods is of particular concern in developing 
countries, because legislation regarding maximum tolerance levels for marketed products is 
often lacking and violation of withholding time set to terminate drug therapy occurs 
regularly. In Nigeria various studies have been conducted confirming the misuse of drugs in 
food animals and residues deposition in meat and animal products (Oboegbulem and Fidelis, 
1996; Dipeolu and Alonge, 2002; Kabir et. al., 2004). Oyekunle and Olubi, (1992) reported 
the occurrence of antibiotic residues in broiler meat while Dipeolu et al., (2005) reported the 
presence of tetracycline residues in eggs marketed in Ogun State. Dipeolu and Ayinde, 
(2001) found tetracycline residue of 0.017-0.039μg/kg in pork produced around Abeokuta, 
Kabir et al., (2004) also reported the presence of antibiotics residues in slaughtered cattle and 
chicken in northern Nigeria. Most of these studies were employed on screening 
microbiological techniques that does not specifically classify and quantify the antibiotics, 
hence the degree of risks to the consumers could not been ascertained and there is the need to 
quantify the levels of residues in meat, milk and eggs available for human consumption in 
Nigeria.  
2.10.5 Nigerian Food and drug Safety Policies 
Good food hygiene and safety with optimum nutritional health for all Nigerians though not 
explicitly expressed, is implicit in the objectives and strategies of the National Health Policy 
and the Abuja Health Declaration (FAO/WHO 2005). Nigeria as a member of the United 
Nations has been a signatory to all the Conventions and Declarations on Health issues 
including codex alimentarius commission and WTO.  Various governments in Nigeria over 
the years have tried in several ways to make provision for the safety and wholesomeness of 
the nation‟s food supply. As far back as 1971 to date, several legislative provisions have been 
enacted in different statutes. These include: 
a) Public Health Laws (1917) now known as Public Health Ordinance Cap 165 of 1958; 
b) The Food and Drugs Decree, No. 35 of 1974; 
c) The Standards Organization of Nigeria Decree No.56 of 1971; 
d) The Animal Disease Control Decree No. 10 of 1988; 
e) The Marketing of Breast Milk Substitute Decree No. 41 of 1990; 
f) The National Agency for Food and Drugs Administration and Control (NAFDAC) Decree 
No. 15 of 1993. 
Most State Governments in the country have promulgated meat edicts for assurance of safety 
of meat and meat products through proper inspection and hygiene practices. Efforts are been 
made to harmonise related laws and meat edicts through the proposed “veterinary public 
health (meat hygiene) act” at the National Assembly. The law when enacted will take care of 
many gaps and lopsidedness in the food hygiene laws. The law is also to control 
transportation and slaughter of food animals and their inspection. It will also regulate 
interstate and international trade on food animal carcasses, meat and other animal by-
products (Aliu, 2004). 
Nigeria food and drug policies began with the food and Drug Act of 1974, followed by Drug 
and Related decree 19 of 1993, the national drug formulary and essential drug list established 
under Decree 43 of 1989 all of which has been encapsulated into National Agency for Food 
and Drug Administration (NAFDAC) decree 15 of 1993 and the amendment by decree 19 of 
1999 for the control of drugs, processed foods and package, water. Animal disease control 
decree 19 of 1988 (repealed the Diseases of Animal Act 1917, 1962) empowered the Federal 
Livestock Division, of Federal Ministry of Agriculture to control exportation and importation 
of live animals, poultry egg, milk sense, other animal products and biological infections 
agents. It also provides for surveillance and control of trade animals within the country. 
Animal disease control decree 1988 (FGN, 1988) saddled the veterinary profession with 
responsibilities of prevention and control of animal diseases of socioeconomic and public 
health significance through the control and prevention of such diseases in livestock by 
ensuring good agricultural practices, good veterinary practices and proper inspection of 
animal products (meat, milk, egg etc) meant for human consumptions as part of food hygiene.  
Meat inspection are being carried out by the Veterinary Department of the State Ministry of 
Agriculture in major abattoirs across the country, however, it is been efficient due to several 
factors including shortage of manpower, inadequate abattoir facilities and lack of coordinated 
livestock production which does not allow for traceability.  Meat inspection is usually based 
on organoleptic visual inspection. In Nigerian abattoirs and slaughter slabs, butchering of 
meat are done on concrete floor with inadequate slaughtering basic facilities including lack of 
potable water resulting in unhygienic processing and handling of meat meant for public 
consumption. Thus, high level of carcass contaminations with biological, chemical and 
physical hazards have been reported (Ojo et al., 2009;). Regulatory Control of livestock 
diseases in Nigeria especially those that are of economic and/or zoonotic importance are 
supposed to be jointly carried out by the Federal, State and to some extent, Local 
Governments Areas (LGAs). Each of these tiers has its own mandatory function or activity 
areas. The function of the Federal Government is mostly in the area of national policy 
formulation and implementation especially in the area of monitoring the activities of the 
States and LGAs to ensure compliance with laid down principles, standards and goals. The 
primary responsibility of disease control in their territories is that individual States who carry 
this out through the provision of Veterinary Clinics, diagnostic laboratories and other 
facilities such as a major abattoirs. Slaughter slabs are managed by Local Govt Councils. 
Also, through the enactment NAFDAC decree No. 15, 1993 (FGN 1993) the National 
Agency for Food and Drug Administration and control (NAFDAC) was established to 
perform the following functions:  
 Regulation and control the importation, exportation, manufacture, advertisement, 
distribution, sale, and use of food, drugs, cosmetics, medical devices, bottled water 
and chemicals; 
 Conducting appropriate tests and ensure compliance with standard
 specifications designated and approved by the council for the effective control
 of the quality of food, drugs, etc., as well as their raw materials and 
 production, including processes in factories and other establishments; 
 Undertaking appropriate investigations into the production premises and raw
 materials for food, drugs, etc. and establish relevant quality assurance systems,
 including certification of the production sites and regulated products; 
  Undertaking inspection of food, drugs etc.; 
 Compiling standard specifications and regulations and guidelines for the
 production, importation, exportation, sale and distribution of food, drugs, etc.  
 Undertaking registration of food, drugs, etc; 
  Establishing and maintaining relevant laboratory or other institutions in
 strategic areas of Nigeria as may be necessary for the performance of its
 functions.  
NAFDAC also participate in international food safety efforts of CAC. It has no paid attention 
to setting and maintaining essential veterinary drug list and veterinary drug residues control 
(Aliu, 2004). Unlike Food and Drug Act (1974) that has veterinary profession and scientists 
in their board, NAFDAC does not have representation of veterinary profession in the council 
and there are few veterinarians in its employment.  However, section 8(g) of NAFDAC 
decree provides for the establishment of directorates, as may be required for proper 
performance of the functions. Veterinary Directorate have been advocated to reflect 
veterinary professions in the agency to adequately cater for veterinary drugs, biologics and 
pesticides chemicals. Also the National Drug Formulary and essential drug list Act 1989, 
does not include veterinary surgeon should be reviewed and define essential drug to satisfy 
and care for the needs of majority of animal and human population the list does not 
accommodate essential veterinary drugs, Biologics and pesticides chemicals. Counterfeit and 
fake drug (Miscellaneous Poisons) Act 1980 dealing with fake drug, does not have vet 
representation at both Federal and State task forces. The veterinary and toxicology training 
make veterinarians vast in the use and possible adverse effects of vet drugs in all species of 
terrestrial and aquatic animals. There are presumably many fake veterinary drugs that are not 
being monitored in Nigeria (Aliu, 2004). Therefore the structure and technical capability of 
veterinary drug use control and monitoring are either lopsided or there is no coordinated 
effort on monitoring and control of antimicrobial use, residue and resistance in Nigeria. This 
study was designed to assess the practice of drug administration in poultry and cattle 
production and characterised the risks of antibiotics residues and resistance meat-borne 
Escherichia coli O157:H7 in the chicken and beef meat for human consumption in selected 
cities of south western Nigeria. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
CHAPTER THREE 
SURVEY OF THE USAGE OF ANTIBIOTICS USAGE BY CATTLE AND 
POULTRY PRODUCERS IN SOUTHWEST NIGERIA 
3.1 Introduction 
Veterinary drugs, including antibiotics are important inputs in livestock production.  
Approximately half of the antimicrobials produced today are used in animal production and 
they represent the largest proportion of pharmaceutical sales both in volume and money value 
of any drugs used in animal production (WHO, 2000). According to Mellon, et al., (2001), 
out of the overall annual 17.5 million kilograms production of antibiotics in the United States 
about 12.5 million kilograms are used for non-therapeutic purposes in livestock production 
while only 1.5 million kilograms are used for human medical therapy. However in Africa, 
reliable data on antibiotic consumption humans and animals are not readily available (Mitema 
et al., 2001). Whereas, developed nations are employing stringent control on the use of 
veterinary drugs to ensure consumer protection, the situation in developing countries is the 
opposite (Mitema et al., 2001; FAO/WHO/OIE, 2008).  
In order to ensure food safety and prevent the side effects associated with the use of 
antibiotics, WHO and OIE recommended “Good Veterinary Practice in the use of 
Antimicrobial” (GVPA) products. GVPA is defined as a rational antibacterial therapy which 
is based on a combination of clinical judgement; laboratory diagnosis; epidemiological 
background and husbandry information about the flock to be treated (WHO, 2000). Drug 
manufacturers, regulatory agencies, veterinarians, livestock producers and their employees 
involved in administering the feed additive have collective responsibility for controlling 
unintended public health impacts of antibiotic use in food-producing animals (WHO, 2001).  
This work was therefore aimed at investigating the culture (i.e knowledge, atttitude and 
practices - KAP) of cattle and poultry producers in south western Nigeria concerning the 
administration of antibiotics to their animals destined for human consumption. 
3.3 Materials and methods 
3.2.1 Sampling Procedures 
Thirty poultry farmers were selected through multi-stage sampling of representative small, 
medium and large scale poultry farms in States under study. Willingness to participate in the 
survey and condition of confidentiality were among the criteria for the selection. Also twenty 
cattle producers at Ibadan and Lagos cattle markets and agropastoralist settlements at the 
peri-urban areas of the cities were also selected for the questionnaire interview. The 
respondents included flocks/herds owners or major operators such as farm managers or 
supervisors. 
3.2.2 Questionnaire interview 
The study was conducted using two sets of semi-structured questionnaire (Appendix IIa and 
IIb). The questionnaire was designed to assess the livestock production system, major health 
problems of their livestock, and the drug administration of veterinary drugs service in the 
study area. The first section was on the respondents‟ production experience, history and 
nature of the flocks or herds. The second section was on the disease status of the herd or 
flocks including their frequently occurrence, diagnosis and treatment sevices employed. The 
names of the diseases were translated from the local names and the description of symptoms 
by the respondents. The next section on antibiotics usage required the respondents to indicate 
the frequency of use antibiotics in feed or water and injection. They were also asked to 
specify, from a list of trade and generic names, the types of in-feed, in-water and injectable 
antibiotics used for their livestock. The final section of the questionnaire was on assessment 
of the respondents‟ knowledge and practice of withdrawal periods.  
3.2.3 Data Analysis 
The data were entered into Microsoft Office Excel Program after which simple descriptive 
statistic and chi square test were employed to analyze the data. 
3.3 RESULTS 
3.3.1 Livestock Farmers Characteristics 
Out of the 30 poultry farmers interviewed, 33.3% were female while 66.7% were male. All 
the cattle producers were males. Their mean age and years of experience are shown on table 
3.1. The majority of poultry producers (64%) had more than 10 years of poultry farming 
experience, with an average of 10.6 years, while the cattle producers had an average of 19.4 
years cattle rearing experience. The education levels of the poultry farmers ranged from 
primary school certificate to university degree among them are three (6.7%) veterinary 
doctors while greater proportion (85.0%) of the cattle farmers did not have formal education 
(Figure 3.1). All the respondents reared the animals for sale and domestic consumption.  
3.3.2 Flock/Herd Structure and Management Systems 
The median cattle herd population reared by the respondents was 32 (range = 10-120), while 
the median poultry flock population was 4,500 (range=250 to 65,000) birds with 83.3% of 
farmers considered “large-scale” producers. Twenty (66.7%) of the poultry farmers were 
engaged in rearing of commercial layers while seven (23.3%) were broiler grow-out farmers, 
while three (10%) others engaged in the rearing of both layers and broilers in their farms and 
twenty farmers reared only commercial layers. Sixty percent of poultry farmers practiced a 
“deep litter” system while 23.3% (n = 7) practiced both deep litter and a “battery cage” 
system to house their flocks.  
 
3.3.2 Feed and Feeding of the poultry and cattle 
The results of the study showed that 83.3% of the poultry farmers were engaged in self feed 
milling for their chickens while 16.7% obtained feed from commercial feed millers. About 
87.7% routinely added premixes and antimicrobials such as oxytetracycline and tylosine in 
feed as egg boosters or growth promoters and disease prevention.  All (100.0%) cattle 
farmers fed the cattle mainly with grasses by pasture grazing with concentrates and grain 
offal as supplements.  Salt lick mineral supplements were giving to the cattle by 60.0% of the 
farmers while 50.0% claimed they used herbal preparations in feeds and drinking water. 
 
 
 
 
 
 
 
 
 
 
 
 
Table 3.1 Farmers characteristics and flock/herd structure 
Variables Cattle farmers Poultry farmers 
 Male 20 (100.0%) 20 (66.7%) 
Gender 
Female 0% 10 (33.3%) 
Owners 14 (70.0%) 12 (40.0%) 
Ownership 
Manager/Supervisor  6 (30.0%) 18 (60.0%) 
Median  age in years(range) 30 (14-60) years 36 (18-63) years 
Mean years of experience in practice ±SD  19.4 ±10.7 years  10.6 ±4.5 years 
Median Flock/herd Population (range) 32 (10-80) heads  4500 (250-62500) 
of cattle chickens 
 
Source; Field survey 2006 
 
 
 
 
 
 
 
3.3.3 Diseases Status of the Poultry and Cattle 
The commonly encountered poultry diseases reported by the respondents include chronic 
respiratory diseases (CRD), helminthosis (worms), Newcastle disease, fowl typhoid 
(salmonellosis), coccidiosis, gumboro disease, fowl cholera, colibacillosis (yolk sac 
infection), infectious coryza, and lice infestation in that order (Figure 3). While the common 
diseases reported by the cattle farmers include helminthosis (worms), mastitis, ticks, 
cough/respiratory diseases, trypanosomosis abscesses, foot rots/lameness, skin 
infection/wounds in the frequencies shown in figures 3.2 and 3.3. These diseases were the 
major challenges which they claimed necessitated regular use of antibiotics for the animals.  
Majority (86.7%) of the poultry farmers did not engage the services of veterinarians for 
disease diagnosis and drugs prescription. They claimed to recognise disease conditions based 
on their knowledge and experience of clinical signs and post mortem findings and only two 
of the poultry farmers 6.7% engaged laboratory confirmation of diseses diagnosis and 
antibiotic sensitivity tests for bacterial isolates. All (100%) the cattle farmers (interviewed) 
also claimed to recognise different diseases and did not engage the services of veterinarian 
for disease diagnosis drug prescription and use. 
 
 
 
 
 
 
Frequencies (%) of poultry diseases 
80 
75 
60 60 
50 46.7 
40 
30 
23.3 
10 
 
Figure 3.1: Commonly encountered poultry diseases reported by the respondents  
 
 
 
 
 
 
 
 
 
 
 Frquencies (%) of cattle diseases 
80 
75 75 
65 
60 
50 
40 40 
 
Figure 3.2: Commonly encountered cattle diseases reported by the respondents 
 
 
 
 
 
 
 
 
  3.3.4 The use of drugs in poultry and cattle  
All the respondents (100%) used antibiotics for prevention and treatment of diseases. Table 
3.2 show the frequencies of indications for the use of antibiotics in poultry and cattle. 
Majority 70.0% of the poultry farmers did not employ the services of veterinarian for 
prescription but were engaged in self administration of drugs to their animals. While 30.0% 
of the respondents reported that they treat their flocks based on professional judgement and 
prescription. However, all (100.0%) the cattle producers treated their animal by themselves 
through experience and they also claimed efficacy of herbal preparations in the treatment of 
cattle diseases. Records of diseases and treatments were not available in most of the surveyed 
farms. The majority of producers used at least 3 antibiotics (n=15) while seven other 
producers reported using between four and six different antibiotics. The majority of 
producers (87.7%) routinely added antibiotics to the feed for disease prevention and to 
improve production. Tetracyclines (oxytetracycline and chlortetracycline) were the most 
commonly used antibiotic (Figure 3.3). Approximately 50% of poultry farmers also used 
gentamicin while 20% of them employed fluoroquinolones (ciprofloxacin or (enrofloxacin) 
and chloramphenicol. The reported common routes of medication are oral in drinking water 
and by intramuscular injections. Also in cattle antibiotics were also frequently being used for 
the treatment of cattle infections and also prophylaxis or as anti-stress. The most frequently 
used antibiotics were oxytetracycline (figure 3.3) either as 5 to 10% short acting or 20% long 
acting (LA), procaine penicillin occasionally combined with dihydrostreptomycin. 
Intramuscular route was the most reported routes of administration of these drugs in cattle.  
These drugs were reported by 83.3% of the farmers to be sourced from veterinary retail 
shops, while 16.7% procured drugs directly from company‟s sales representatives and 
hawkers. Also, all the cattle farmers (100.0%) reported the therapeutic efficacy of herbal 
preparations.  
Table3.2: Indications for the use of Antimicrobials in Poultry and cattle 
Indication for use Poultry Cattle  
Frequency (%) Frequency (%) 
Prophylaxis 26 (86.7) 20 (100.0) 
Therapeautics 30 (100.0) 20 (100.0) 
Egg booster 16 (53.3) 0 (0.0) 
Growth Promotion 7 (23.3) 8 (40.0) 
Source; Field survey 2006 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 3.3: Commonly used antibiotics in poultry and cattle production 
 
 
 
 
 
 
 
 
 
3.3.5 Farmers knowledge of withdrawal period and drug residues 
An overall of 60% of the respondents claimed to have knowledge on antimicrobial 
withdrawal period but only 16.7% of the poultry farmers complied with withdrawal periods 
before culling, slaughter or sales of birds.  Most of the respondents could not comply with 
withdrawal period as they could not understand the practicality of withholding the sales or 
consumption of their eggs or chickens. Culling and dressing of treated chickens were done by 
some farmers to avoid total loss. All the respondents who are egg producers admitted that 
they sold or ate their eggs immediately during and after the use of veterinary drugs in the 
flock for treatment or prophylaxis. On the cattle farms, milk and milk products from 
unaffected quarters of the udders of treated cows were reported being sold for consumption. 
Cattle that were given antibiotics prophylactically or as anti-stress were also sold for 
slaughter. Table 3.3 shows the levels of compliance of the farmers to withdrawal periods of 
the drugs.  None of the cattle producers observed withdrawal periods while only 16.7% of the 
poultry farmers interviewed claimed that they observed the withdrawal periods. The results 
obtained on the farmers‟ knowledge of the effects of antimicrobial use and residues on human 
health vary from no effect to risks of cancers and drug resistance as shown in Figure 3.5. 
 
 
 
 
 
 
Table 3.3: Compliance with Withdrawal Period among the Poultry and cattle farmers 
Compliance Poultry  Cattle  
Frequency (%) Frequency (%) 
Yes 5(16.7) 0 (0.0) 
No 25 (83.3) 20 (100.0) 
 Source; Field survey 2006 
 
 
 
 
 
 
 
 
 
 
 
 
 
resistance , cancer, 5% 
10% 
not sure, 45% allergy, 10% 
no effect, 25% reduced 
production, 
5% 
 
Figure 3.4: Farmers knowledge of the effects of drugs residues in egg/meat 
 
 
 
 
 
 
 
 
 
 
3.4 Discussion 
Agricultural use of antibiotics has become a very important public health concern (White et 
al., 2001). This study showed that majority of cattle and poultry farmers interviewed 
depended on the use of different antimicrobial agents (including herbal preparations). The 
practice was indiscrimate, since majority of the farmers (86.7% poultry farmers and 100% 
cattle producers) did not engage the services of veterinarians or laboratories for disease 
diagnosis, antibiotic prescription and usage in these food animals. This practice is could be 
associated with the low education and lack of awareness of health risks of such practices.  
Also, since most of the farmers have more than 10 years of livestock rearing experience, 
there was a general assumption among them that they could recognise the disease status of 
their flocks or herds/ flocks. This attitude led to unprofessional disease diagnosis and drugs 
usage. Therefore, hypothesis (Ho1) is not rejected. 
The prevalence of different diseases reported among the herds and flocks could have resulted 
from wrong diagnosis and improper dosing with drugs which could aid the development and 
spread of resistant strains of pathogens within the flocks and herds. The unrestricted access to 
veterinary drugs (including antibiotics) by the farmers due to over the counter availability of 
these drugs without veterinary prescription or supervision is an indication of lack of proper 
regulatory control and monitoring of the use of antibiotics in the study area. These agree with 
the findings of various authors in Nigeria and other developing countries (Okolo, 1986; 
Mitema et al., 2001; Dipeolu, 2002; Kabir et al., 2004).  
In this study most of the farmers (95%) were neither aware nor observed withdrawal periods 
before selling or consuming the poultry and cattle products, coupled with lack of proper 
records of treatment as reported in other studies in developing countries (Mitema et al., 2001; 
Kabir et al., 2004; Sasanya et al., 2005) predisposed the meat to residues deposition. 
therefore hypothesis (Ho2) is not accepted (rejected). Such practices without observance of 
the withdrawal period could result in the presence of residues in the meat, milk and eggs from 
the herds/flocks thereby predisposing the consumers to some levels of antibiotics residues 
and it attendant public health consequences (Riviere and Spoo, 1995). In the case of 
commercial laying birds the compliance with the withdrawal period during the course of 
antibiotics treatment was queried by the farmers on the ground of economic losses as they 
claimed that the proceed from the eggs were used to purchase for the chicken to boost egg 
production and to treat or prevent diseases which were the constant challenges. Hence 
withdrawal period was not practicable in eggs of treated laying birds. The indiscriminate use 
of several antibiotics by self prescription and medication by livestock producers could be due 
to: weak veterinary structure and inadequate control of veterinary drugs in developing 
countries (Dina and Arowolo, 1991; Fingleton, 2004; Noga, 2009). 
Most of the antibiotics used in these animals are analogues of and fully cross resistant with 
important antibiotics that are used in human medicine (van den Bogaard, 2000). As a result of 
indiscriminate and regular exposure of food animals to antibiotics, the prevalence of resistant 
bacteria in the faecal flora of these animals is high. These resistant bacteria can be directly 
and indirectly, via foods of animal origin, transferred to humans and either colonize the 
human intestinal tract or exchange their resistance genes among the commensal and 
pathogenic bacteria (van den Bogaard, 1998).  Witte, (1998) reemphasized the human health 
risks associated with the use of antibiotics in agriculture by citing specific examples of 
avoparcin-related, vancomycin-resistant enterococci disease transfer from animals to humans 
and the speculation about the relationship between satA-gene-mediated streptogramines-
resistance development and the use of virginiamycin in food animals.  
Other consequences of lack of accountability and inappropriate use of antibiotic in human, 
veterinary medicine and in agriculture include: shortened lifespan of an antibiotic‟s 
usefulness, additional complications in surveillance, inability to predict resistance patterns 
and the consequences on human, animal and environmental health. Over-the-counter 
availability of antibiotics for domestic animals and the absence of professional oversight in 
many uses have been responsible for the frustration of regulatory officials on accountability 
and limit the ability to make a true estimate of the magnitude of resistance problems that 
threaten human and animal health (National Research Council, 1998).  
In this study most of the farmers (95%) did not observe withdrawal periods with lack of 
proper records of treatment as reported in other studies in developing countries (Mitema et 
al., 2001; Kabir et al., 2004; Sasanya et al., 2005) predisposed the meat to residues 
deposition. Dipeolu et al., (2005) reported that poultry farmers in Nigeria could not observe 
withdrawal periods following the use of antibiotics as feed additive and growth promoters, 
especially in laying birds as the poultry producers were selling eggs from both medicated and 
unmediated flocks for public consumption.  Such practices enhance the presence of 
antibiotics residues at violative levels in food of animal origin against CAC and SPS 
standards and are inimical to food safety and public health. However, good animal husbandry 
and hygienic measures can prevent contamination and disease outbreak thereby reducing the 
need for antibiotics use. Appropriate use of antibiotics for food animals is crucial to the 
preservation of long-term efficacy of existing antibiotics, support animal health and welfare, 
and limit the risk of transfer of antibiotic residue and resistance pathogen among man, 
animals and the environment. 
 
 
 
CHAPTER FOUR 
DETECTION OF ANTIBIOTIC RESIDUES AND QUANTITATIVE ANALYSIS OF 
OXYTETRACYCLINE RESIDUES IN CATTLE AND CHICKEN MEAT IN 
SOUTHWEST NIGERIA 
4.1 Introduction 
Antimicrobials are among the inputs usually employed in commercial livestock production. 
Food animals treated with antibiotics and their edible products are required to be held for 
specific withdrawal periods so that their residues are depleted to safe level before such animal 
tissues can be used as food for human consumption (KuKanich et al., 2005). In Nigeria like 
most developing countries antibiotics are used in animals indiscriminately by livestock 
producers for the prevention and treatment of bacterial infection and the drugs are available 
over the counter (Dina and Arowolo 1991; Kabir et al., 2004). A greater proportion of cattle 
in Nigeria are reared by the nomadic herdsmen who administer chemotherapeutic agents 
without veterinary prescription (Dipeolu and Alonge, 2002; Kabir et al., 2004) while poultry 
farmers also routinely use antibiotics for their flocks. Correct dosage was unlikely being 
administered and the withdrawal periods are not usually observed.  
Tetracyclines are broad-spectrum antibiotics that show activity against Gram-positive and 
Gram-negative bacteria, including mycoplasmas, chlamydiae, rickettsias, spirochetes, 
actinomycetes, and some protozoa (Sundin, 2003). This group of antibiotics have been used 
for more than 50 years for the treatment of bacterial infections in both humans and animals. 
They are among the most frequently used groups of antimicrobials animal-food production 
for prophylaxis, chemotherapy and growth promotion (Mitchell, et al., 1998; Karimuribo et 
al., 2005; Nonga et al., 2009). Despite early warnings about increasing resistances of 
microorganisms to tetracyclines and the banning of tetracyclines as growth promotors, more 
than 65% of the antibiotics prescribed for veterinary therapeutic use within the European 
Community (2294 of 3494 tons) are tetracyclines (Sarmah et al., 2006). In the United States, 
tetracyclines are the most commonly used antibiotics in a variety of animal species (disease 
treatment and prevention; growth promotion), plants, and humans (Mellon et al., 2001).  
Consequently, residues of the commonly used tetracyclines (oxytetracycline, tetracycline, 
chlortetracycline and doxycycline) are found in meat, milk and eggs (Okerman et al., 1998). 
The adverse effects of tetracyclines and their residues on consumer‟s health include allergic 
reactions, discolouration of teeth, chronic nephrotoxicity, hepatotoxicity, skin 
hyperpigmentation, gastrointestinal disturbance due to the selective pressure of antibiotics on 
human gut micro flora and development of antibiotic-resistant bacteria (Robert, 1996; 
Goldfrank et al., 2002). The residual presence of tetracyclines in milk also causes 
technological difficulties in the milk processing industry (Heeschen and Bluthgen 1991).  
Imprudent use of antibiotics could result in the occurrence of residues in meat, milk and eggs 
with consequent public health hazards (Heeschen and Bluthgen 1991). The widespread use of 
antimicrobials in livestock management and possible violations of MRLs require routine 
monitoring and surveillance of the use of veterinary drugs and drug residues. However, in 
Nigeria there are no residues inspections and monitoring programmes in place, coupled with 
the unregulated access to veterinary drugs by livestock producers the risks of residues in meat 
eggs or milk are very high. Therefore there is need for routine screening and surveillance of 
food of animal origin for residues of veterinary drugs. 
Generally antibiotics residues screening of veterinary drugs is performed using 
microbiological inhibition methods, which allow their detection and/or semi-quantitative 
determination, and using specific rapid testing (Mitchell et al., 1998; Botsoglou and Fletouris 
2001; Nonga, 2009). Traditionally, the methods require overnight (24h) incubation may be 
very time-consuming and are considered as multi-residue screening tests for antibiotics. 
However, inhibition tests may be of high sensitivity but they lack specificity as they cannot 
distinguish among different forms of antibiotics, therefore every inhibition test can only be 
used as a tool for screening. In Nigeria various studies have been conducted on drug residues 
deposit in food animal products in Nigeria (Oboegbulem and Fidelis, 1996; Dipeolu and 
Alonge 2002; Kabir et al., 2004) have demonstrated the presence of antibiotic residues in 
meat and animal products. Most of these studies were based on microbiological inhibition 
techniques that did not specifically classify and quantify the antibiotics and require 24 hours 
incubation. Also, there are no national MRLs or residues inspection and monitoring 
programmes in place, coupled with the unregulated access and use of veterinary drug 
(including antibiotics) by livestock producers in Nigeria. The risks of residues in meat, eggs 
or milk are therefore very high. To protect consumers from exposure to residues and the 
public health consequences, the FAO/ WHO Codex Alimentarius Commission and other 
national agencies have established and allocated MRLs for tetracyclines in food items. The 
maximum residual limit set by the EU legislation for tetracycline, oxytetracycline as well as 
chlortetracycline in raw cow milk is set to 0.1 mg/kg (100 ng/g) (Council Regulation 
2377/90/EEC), while CAC (2009) recommended maximum residue limit (MRL) is 200μg/kg 
in muscle, 600μg/kg in liver and 1200μg/kg in kidney. 
There is need for rapid screening of large quantity of meat, milk or eggs to protect the 
consumer against antibiotic residues; this requires rapid detection techniques for which 
®
several commercial kits have been developed. Premi Test (DSM, the Netherlands), is a 
commercially available rapid microbiological screening kit developed for antibiotic residue 
®
detection. Premi Test kit ampoule contain an agar medium, imbedded spores of Bacillus 
stearothermophilus var. calidolactis which is sensitive to wide range of antibiotics. 
®
Premi Test is an agar diffusion test with colour change indicator in the medium producing 
result within 4 hours of incubation. Samples of chicken and beef sold for public consumption 
in Ibadan, Lagos and Akure were screened to determine the prevalence of antimicrobial 
®
residues in the tissues using Premi Test kit and to analyse the levels of oxytetracycline 
residue in the samples. 
4.2 Materials and Methods 
4.2.1 Samples collection 
Three municipal/metropolitan abattoirs namely, Oko-Oba, Bodija, Araromi abattoirs in 
Lagos, Ibadan and Akure respectively were visited where edible portions (muscle, kidney and 
liver) of beef were purchased in most cases or obtained through the effort of the meat 
inspectors and veterinary officers of the State Department of Veterinary Services from the 
abattoirs between June 2007 and May 2009.  Broiler chicken liver and breast/thigh muscle 
from chicken slaughtering markets at Oko-Oba (Lagos), Mokola (Ibadan) and ten commercial 
broiler farms from Ibadan and Lagos were obtained. Chicken samples were collected from 
and Oko-Oba and Mokola chicken markets where live chickens from different farms in 
southwest poultry are sold live or dressed. Also ten commercial broilers grow-out farms were 
selected and prior visited to obtain appointment for the time of slaughtering of broiler 
chickens in Ibadan and Lagos.  
The sampling was conducted between January 2007 and December 2009. Sample sizes of 
200 each of  cattle carasesses and 200 chicken were chosen using range 19 to 299 (at 1 to 
15% non-compliance incidence at 95% CI) from CAC non-compliance prevalence table of 
random sampling for residue(Appendix v) according to CAC/GL, (2009) based on 15.6% and 
prevalence obtained by Dipeolu (2002) in beef and 33.1% by Kabir et al., (2004) in chicken 
from Nigeria.  
 Approximately 200 grams portions from retailed liver, kidney and muscle from 250 
carcasses of cattle slaughtered for public consumption were obtained twice (during wet and 
dry seaons) from each municipal abattoir at Araromi (Akure), Bodija (Ibadan) and Oko-Oba 
(Lagos).  Also, 200 breast muscle and liver samples of  broiler chickens from Mokola and 
Oko-Oba live-birds slaughter markets and ten commercial broilers farms each from Ibadan 
and Lagos were aseptically collected into sterile plastic bags (Whirl-Pak, Nasco USA).  The 
distributions of the samples are shown on table 4.1a and 4.1b. The samples were transported 
in cool boxes packed with ice packs to the laboratory of the Department of Veterinary Public 
Health and Preventive Medicine, University of Ibadan, for analysis.  
 
 
 
 
 
 
 
 
 
 
 
 
Table 4.1a: Distribution of beef samples 
Location Wet season Dry season Total 
(Abattoir) Kidney Liver Muscle Kidney Liver Muscle Total 
Akure 250 250 250 250 250 250 1500 
(Araromi) 
Ibadan 250 250 250 250 250 250 1500 
(Bodija) 
Lagos 250 250 250 250 250 250 1500 
(Oko-Oba) 
Total 750 750 750 750 750 750 4500 
 
Table 4.1b Distribution of chicken samples 
Location Liver Muscle Total 
Ibadan(Mokola market) 200 200 400 
Ibadan (broiler farms) 200 200 400 
Lagos (Oko-Oba market) 200 200 400 
Lagos (broiler farms) 200 200 400 
Total 800 800 1600 
 
 
 
 
4.2.2 Screening of Beef and Chicken for Antimicrobial Residues 
The prevalence of antimicrobial residues in the meat samples was determined by rapid test 
®
Premi Test antibiotics screening kit following the manufacturer‟s (DSM, Netherlands) 
protocol. The test involved a simple process of meat juice extraction and incubation in agar 
imbedded with spores of Bacillus stearothermophilus var. calidolactis and containing acid-
®
based indicator bromocresol purple. Premi Test combines the principle of an agar diffusion 
test with colour change by the indicator. There active metabolism of the seeded micro-
organism not inhibited by residue in negative samples makes the agar test changed colour 
from purple to yellow. But when the growth of the microorganism is inhibited (due to 
presence of an antibiotic at or above the limit of detection or LOD) the test remained purple. 
3
Approximately 2cm  each of kidney, liver and muscle was cut into the meat press to extract 
the meat juice from which 100µl was carefully pipetted onto each ampoule of the agar. The 
agar with the extract was allowed to stand for 20 minutes for pre-diffusion at room 
temperature and then flushed carefully twice with distilled water. Once the agar was drained 
of the extract and water the ampoules were closed with foil. These were incubated in the 
0
heating block for about 3hours at 64 C after which the result were observed through colour 
changes. The colour of all ampoules was read at the moment the negative control changed 
colour from purple to yellow and the results were recorded as positive or negative for 
antimicrobial residues. 
 
 
 
 
 
 
4.2.3 Chromatographic Analysis of Oxytetracycline Residue in beef and Chicken 
4.2.3.1 HPLC Chromatographic conditions 
®
HPLC Machine; Buck-Chrom  HPLC (Buck Scientific, USA) with UV/Visible detector was 
set at the following conditions: Wavelength set at 360nm, Stationary phase: reversed phase 
C18, 10µm Nucleosil 4.6 x 250mm ID column, Mobile phase: Methanol, Acetonitrile, 0.01M 
aqueous Oxalic acid (1:1.5:2.5) at pH 2, Flow rate: 1.5ml/minute, Injection volume: 20µl 
4.2.3.2 Sample Preparation 
Sixty samples of each of the meat types of cattle and chicken that were positive for 
antimicrobial residues by Premi®Test from each location were randomly selected for 
quantitative analysis of oxytetracycline residue. The samples were taken through three stages 
of preparation (a) homogenization and extraction of the sample residues by hydrochloric 
acid; (b) precipitation of proteins using acetonitrile and filtration; and, (c) clean-up by liquid-
liquid partition with methylene chloride and hexane according to methods developed by 
Moats (1986) and used by Ibrahim and Moats (1994).  
The extraction and clean-up procedures developed by Moats (1986) and used by Ibrahim and 
Moats (1994) was employed in this study. This involves Liquid - Liquid partitioning 
extraction procedures to obtain the analyte. The extraction process was done by cutting 
approximately 25g of each sample which was thoroughly homogenized thrice with 3 
volume/weight of 1N hydrochloric acid. Protein precipitation was done by adding 8ml of 
the homogenate which was thoroughly swirled with 32mls acetonitrile in a conical flask and 
allowed to stand for 5minutes after which the supernatant was filtered through a plug of glass 
wool on the stem of a glass funnel. The sample clean-up was achieved by adding 20 mls of 
the filtrate to 20mls hexane and 20mls methylene chloride in a separatory funnel and 
vigorously shaken resulting in separation into two layers. About 4mls of the water layer 
containing the analyte were collected to scintillation vials for HPLC analysis.   
4.2.2.3 Preparation of Standard Curve  
One hundred milligrams of oxytetracycline hydrochloride analytical standard was accurately 
weighed and put in a 100 ml volumetric flask, the powder was dissolved in 100 ml of 
methanol to produce a stock solution of 1,000 ppm. The absorbance was determined using 
UV-Spectrophotometer to be 360 nm.  Serial dilutions of the stock solution were carried out 
to give the following dilutions: 1: 100 (10 ppm), 1: 200 (5 ppm), 1: 400 (2.5 ppm), 1: 500 
(1.25 ppm), 1: 1000 (0.1 ppm), 1: 10000 (0.01 ppm), 20µl of the final concentrations were 
used to prepare the standard curves obtained from the chromatograph of the standard solution 
(figure 4.3). The corresponding concentrations of these dilutions (ppm were: 10, 5, 2.5, 0.1, 
and 0.01) were injected to the HPLC machine to obtain the calibration curve, the peak areas 
were plotted against the corresponding concentrations, the best line of fit was plotted using 
Microsoft Excel programmes.  
4.2.2.4 Procedure for HPLC analysis of oxytetracycline  
The analysis and quantification of the oxytetracycline residues in the analytes were 
performed at the Chemical Analysis Laboratory of the Nigeria Institute of Science Laboratory 
Technology (NISLT), Ibadan using a high-performance liquid chromatography machine 
(Buck chrome) equipped with a constant flow pump and a variable wavelength UV detector 
set at 360nm and flow rate of 1.5mls/min. Elution of oxytetracycline from the analyte was 
done on a nucleosil C- 18 (10µm, 250 x 4.0mm 1D) column with mobile phase; Methanol-
Acetonitrile-0.01M aqueous Oxalic acid solution, pH 2.0 (1: 1.5: 2.5) as described by 
Muriuki et al., (2001). The mobile phase was filtered through 0.22µm membrane filter using 
vacuum pump and regularly degassed by sonication. The HPLC machine was also flushed at 
interval with blank methanol and mobile phase was allowed to run through the machine for 
equilibration and conditioning during which stable baseline was obtained on the recorder 
monitor. The column and tubing were regularly checked to ensure leak proof, 20µl of analyte 
from each sample (in duplicate) was injected to the column when the machine gave 
instruction “waiting for pulse injection”. Oxytetracycline was eluted on the C-18 column and 
resolution occurred in the detector resulting in peaks (chromatographs) shown on the monitor 
with the peak areas and retention times recorded by the computer recorder (figure 4.4). The 
mean peak areas of the samples corresponding to the retention time between 2.8 to 3.5 
minutes obtained from the reference standard were recorded as positive for oxytetracycline. 
Quantification of oxytetracycline residues in the samples were obtained from calculation by 
substituting the mean peak areas in the linear equation obtained from the calibration curve of 
the standard. 
4.2.2.5 Recovery Experiment 
This was to determine the sensitivity of the procedure and the rate of residue recovery from 
the extraction and detection procedures. About 25g each of liver kidney and muscle from 
antibiotic free broiler chicken were accurately weighed and spiked in triplicate with 4 ppm 
and 8ppm of the analytical standard oxytetracycline solutions. The tissues were allowed to 
equilibrate for about 30mins before proceeding with extraction and further HPLC analysis as 
above to determine the recovery rate. 
4.2.2.6 Statistical Analysis   
The data were analyzed using descriptive (percentage, range, mean ± SD) and inferential 
statistics. Prevalences of antibiotic residues were compared by chi-square (χ2) test while the 
mean oxytetracycline residues levels in different tissues were analysed by student‟s t-test, 
ANOVA followed by Tukey‟s multiple comparison test at a confidence level of 95% (p < 
0.05) using GraphPad Prism 4.0 (GraphPad Software Inc., San Diego, CA).  
4.4 Results 
4.3.1 Prevalence of antimicrobial residues in beef 
Out of a total of 4500 tissues of cattle samples screened from cattle the three abattoirs in both 
dry and wet seasons 2042 (45.4%) were positive for antimicrobial residues. The results of 
screening of the different edible portions of bovine carcasses from the three abattoirs are 
shown on table 4.2. The highest prevalence (62.8%) occurred during the wet season and in 
the liver samples from Bodija abattoir in Ibadan. 
Results from Bodija abattoir indicated an overall prevalence of 53.3% during the wet season 
compared with 43.2% during the dry season. Also meat from Oko-Oba abattoir yielded an 
overall prevalence of 47.2% and 41.8% during the dry and wet seasons respectively. While 
beef samples from Araromi abattoir had total prevalence of 44.9% and 43.4% prevalence of 
antimicrobial residues during the wet and dry seasons respectively. Liver and kidney samples 
yielded more residue prevalence than the muscle.  
 
 
 
 
 
 
R
Table 4.2 Premi Test Screening of beef for antimicrobial residues 
Location  City Type of DRY SEASON  WET SEASON  
(abattoir)  samples  
No of samples No +ve with No of samples No +ve with 
Premi®Test Premi®Test (%) 
(%) 
Akure  Kidney  250 112 (44.8) 250 123 (49.3) 
(Araromi) 
Liver 250 124 (49.6) 250 128 (51.8) 
Muscle 250 74 (29.6)**  250 86 (34.4)**  
Total  750  310 (41.3)  750  337 (44.9)  
Ibadan (Bodija) Kidney  250 99 (39.6) 250 110 (44.0) 
Liver 250 126 (50.4) 250 157 (62.8)*  
Muscle  250  102 (40.8)**  250  133 (53.2)*(**)  
Total  750  327 (43.2)  750  400 (53.3)  
Lagos (Oko- Kidney  250 109 (43.6) 250 125 (50.0) 
Oba) 
Liver 250 117 (46.8) 250 123 (49.2) 
Muscle 250 88(35.2)**  250 106 (42.4)**  
Total  750  314 (41.8)  750  354 (47.2)  
,
*  ** Significantly difference p<0.05 
 
 
Figure 4.1: Seasonal prevalence of antimicrobial residues in beef from abattoirs in the cities 
 
 
 
 
 
 
 
 
 
 
 
 
4.3.2 Prevalence of antimicrobial residues in chicken 
The overall prevalence of antimicrobial residues obtained from all the chicken samples was 
69.1%. The prevalence in the different chicken tissues across the different locations is shown 
on table 4.3 and figure 4.2. The liver of chicken from market yielded higher prevalence than 
the liver and muscle from farms. Table 4.3, figure 4.2 and appendix II showed the patterns of 
antimicrobial residues prevalence in the chicken samples from Ibadan and Lagos. The data 
indicated that more chicken samples from Ibadan contained the residues than from Lagos but 
the difference was no statistical significant. However, the prevalence of antimicrobial residue 
in the chicken liver was significantly higher (p<0.05) than in the chicken muscle. Also the 
results showed that the prevalence of antimicrobial residues in chicken is higher than in 
cattle. 
 
 
 
 
 
 
 
 
 
 
Table 4.3: Prevalence of antimicrobial residues in chicken from Ibadan and Lagos  
Location Portion of No of samples (n) No +ve with Premi®Test 
chicken (%) 
Ibadan (market) Liver 200 160 (80.0) 
Muscle 200 144 (72.0)  
Ibadan (farms) Liver 200 144 (72.0) 
Muscle 200 134 (67.0) 
 Total  800 582 (72.8) 
Lagos (market) Liver 200 160 (80.0) 
Muscle 200 120 (60.0) 
Liver 200 124 (62.0) 
Lagos (farms) Muscle 200 120 (60.0) 
Total  800 524 (65.5) 
 
 
 
 
 
 
Figure 4.2: Prevalence of antimicrobial residues in chicken 
90 
80 
70 
60 
50 
40 
liver 
30 
muscle 
20 
10 
0 
market farms market farms 
Ibadan Lagos 
Location 
 
®
Figure 4.2 Prevalence antimicrobial residues in chicken meat by Premi Test Screening.  
 
 
 
 
 
 
 
 
 
 
 Residue prevalence (%)  
4.3.3 Results of oxytetracycline residue 
4.3.3.1 Calibration Curve and Recovery Experiment 
The results of the standard concentrations and the peak areas were ploted as the standard 
curve (figure 4.3) with using linear regression equation The linear equation Y = a + b X was 
2
obtained where Y = peak area (cm ), a = Y-intercept, b = the slope, X = concentration of the 
2
oxytetracycline (ppm), y = 20.7x + 8.611 and R  value of 0.993, where y is the peak area and 
2
x is the concentration in ppm. The R  value > 0.9 showed the linearity. The detection limit for 
oxytetracycline was 0.01ppm while the retention time of the oxytetracycline ranged between 
2.8 to 3.5 minutes. The mean retention time for the oxytetracycline is 3.02 minutes while the 
detection limit was 0.01ppm. The mean recovery of oxytetracycline from the spiked tissues 
was between 80.0%-92.5% as shown in table 4.4 with recovery was highest in the muscle 
followed by kidney. The chromatographs of oxytetracycyline standard and tissue residues are 
shown in figures 4.4a and 4.4b.  
 
 
 
 
 
 
 
250 
y = 20.715x + 8.611 
200 R² = 0.993 
150 
100 
50 
0 
0 2 4 6 8 10 12 
conentration (ppm) 
 
Figure 4.3 Calibration curve of oxytetracycline analytical standard. 
 
 
 
 
 
peak area (mVs) 
      
 
Figure 4.4a: Chromatographs of oxytetracycline standard 
 
                                      
                                       
                              
Figure 4.4b: Chromatographs of oxytetracycline in meat samples 
 
 
 
 
 
 
 
 
Table 4.4: Recovery of oxytetracycline from spiked tissues. 
Sample Concentration of Mean recovery Percentage recovery 
Oxtetracycline (ppm) %(SD) 
(ppm) 
Muscle 8 7.2 90.0 (0.35) 
Kidney 8 7.0 87.5 (0.45) 
Liver 8 6.8 85.0 (0.46) 
Muscle 4 3.7 92.5 (0.21) 
Kidney 4 3.6 90.0 (0.32) 
Liver 4 3.2 80.0 (0.30) 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
  
      
 
 
 
4.3.3.2  Prevalence of oxytetracycline residue in beef 
The overall prevalence of 56.2% oxytetracycline residue was obtained in beef across the 
study area with their distributions in the different abattoirs during the different seasons shown 
in table 4.5. The prevalence of 41.9% of the samples contained oxytetracycline above MRL 
(table 4.6). Also in the chicken, an overall prevalence of oxytetracycline residue obtained was 
68.1% with 54.8% of the chicken containing the residue above the MRL. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Table 4.5 Seasonal prevalence of oxytetracycline residue in beef   
Abattoir Wet season Dry season 
Kidney  (%) Liver  (%) Muscle(%) Kidney(%) Liver (%) Muscle(%) 
n=60 n=60 n=60 n=60 n=60  n=60 
Akure 38 (63.3) 36 (60.0) 33 (55.0) 31 (51.7) 34 (56.7) 29 (48.3) 
(Araromi) 
Ibadan 44 (73.3) 37 (61.7) 34 (56.7) 35 (58.3) 32 (53.3) 28 (46.7) 
(Bodija) 
Lagos 34(56.7) 30(50.0) 29(48.3) 36(60.0) 36(60.0) 32 (50.7) 
(Oko-Oba) 
Overall oxytetracycline prevalence in beef= 607 (56.2%), n=1080 
 
 
 
 
 
 
 
 
 
Table 4.6: Prevalence of oxytetracycline in beef above the MRLs 
Abattoir Wet season Dry season 
Kidney (%) Liver  (%) Muscle (%) Kidney (%) Liver  (%) Muscle (%) 
n=60 n=60 n=60 n=60 n=60 n=60 
Akure 16 (26.7) 26 (43.3) 31 (51.7) 27 (45.0) 18 (30.0) 24 (40.0) 
(Araromi) 
Ibadan 32 (53.3) 28 (46.7) 34 (56.7) 18 (30.0) 24 (40.0) 27 (45.0) 
(Bodija) 
Lagos 19(31.7) 24 (40.0) 28 (46.7) 24 (40.0) 25 (41.7) 27 (45.0) 
(Oko-Oba) 
Overall oxytetracycline >MRLs in beef= 452 (41.9%), n=1080 
 
 
 
 
 
 
 
 
 
 
 
4.3.3.3 Prevalence of xytetracycline residue in beef from Ibadan (Bodija) abattoir 
Table 4.7 shows the results of HPLC analysis of the samples from Bodija abattoir (Ibadan) 
with 73.3, 61.7 and 56.7% of the kidney, liver and muscle respectively having detectable 
oxytetracycline residue during the wet season, while 58.3, 53.3 and 46.7% of the meat 
respectively also contained oxytetracycline residue during the dry season. The mean 
oxytetracycline concentrations in the different meat types ranged between 766.2 and 1544.0 
µg/kg during the wet season and between 555.8 and 1354.0 µg/kg in dry season.  These 
results also showed that variable proportions of the meat contained the residues above MRLs 
(violative levels).  
 
 
 
 
 
 
 
 
 
 
 
 
Table 4.7: Oxytetracycline residue in beef from Ibadan (Bodija) abattoir 
Location (season)  Ibadan (wet season)  Ibadan (dry Season) 
Portion of carcasses Kidney Liver Muscle Kidney Liver Muscle 
Range 598.1-5059.0 163.6- 211.9- 163.6- 110- 67.1-
concentration(µg/kg)   2544.0 2790.0 3736.0 2191.0 1245.0 
a
Mean residue level 1544±870.8  917.5 766.2 1354 949.5 555.8 
 a  a  b  b  b
±SD (µg/kg) ±465.2  ±513.9  ±696.5  ±505.6  ±277.8  
Samples positive for 73.3 61.7 56.7 58.3 53.3 46.7 
oxytetracycline (%) 
n=60 
Samples with 53.3 46.7 56.7 30.0 40.0 45.0 
oxytetracycline levels 
above MRLs (%) 
 a, b 
Superscripted values in columns are significantly different (p< 0.05). 
 
 
 
 
 
 
 
 
4.3.3.4 Prevalence of oxytetracycline residue in beef from Akure (Araromi) abattoir  
The results of the quantitative (HPLC) analysis of meats from Araromi abattoir in Akure as 
shown in table 4.8 indicated that oxytetracycline was detectable in 63.3, 60.0 and 55.0% of 
kidney, liver and muscle samples respectively during the wet season and 51.7, 56.7 and 
48.3% of the meat respectively during the dry season. The mean concentrations of 
oxytetracycline residue obtained from the different meat types in this abattoir ranged between 
587.7 and 1185.0 µg/kg with variable proportions containing the residue above codex (CAC) 
recommended MRLs (table 5.5) There mean residue concentrations in muscle liver and 
kidney were significantly different (p< 0.05) with kidney having the highest followed by 
liver. However, there was no significant difference (p>0.05) in the tissues residue 
concentrations of wet season compared with the dry season.  
 
 
 
 
 
 
 
 
 
 
Table 4.8: Oxytetracycline residue in beef samples from Akure (Araromi) abattoir 
Location (season)  Akure (wet season)  Akure(dry Season) 
Portion of Kidney Liver Muscle Kidney Liver Muscle 
carcasses 
Range mean 482.2- 163.6- 163.6- 308.4- 86.4- 67.1-
concentration(µg/kg) 2915.0 2544.0 1660.0 2770.0 1737.0 1187.0 
Mean residue level 1185  945.2* 692.6** 1162 661.7* 587.7** 
      
±SD (µg/kg) ±581.1  ±541.2  ±376.2  ±685.1  ±387  ±321.4  
Proportion of 63.3 61.7 55.0 51.7 56.7 48.3 
samples with 
detectable 
oxytetracycline (%) 
n=60 
Samples with 6.4 10.4 12.8 4.0 7.2 9.6 
oxytetracycline 
levels above MRLs 
(%) 
Superscripted values*, ** in columns are significantly different (p< 0.05). 
 
 
 
 
 
 
4.3.3.5 Prevalence of oxytetracyline residue in beef from Lagos (Oko-Oba) abattoir 
The HPLC results of bovine meat samples from Oko-Oba abattoir in Lagos as shown in table 
4.9 indicate that oxytetracycline residue was detectable in 56.7, 50.0 and 48.3% of kidney, 
liver and muscle respectively during the wet season and in 60.0, 60.0 and 50.78% of the 
different meat types respectively during the dry season from the same abattoir. The mean 
concentrations of oxytetracycline were 1267 ±476.4 SD, 904.9 ±421.4SD and 729.6 ±374.3 
SD µg/kg in kidney, liver and muscle respectively. The results also indicated that 31.7, 40.0 
and 46.7% of kidney, liver and muscle respectively from Oko-Oba abattoir respectively 
contained oxytetracycline at concentrations above the CAC recommended MRL during the 
wet season and in 40.0, 41.3and 45.0% of the different meat types respectively during the dry 
season. There mean residue concentrations in muscle liver and kidney were significantly 
different (p< 0.05), but there was no significant difference (p<0.05) in the tissues residue 
concentrations of wet season compared with the dry season. 
 
 
 
 
 
 
 
 
 
Table 4.9: Oxytetracycline residue in beef from Lagos (Oko-Oba) abattoir 
Location  Lagos (wet season)  Lagos (dry Season) 
(season) 
Portion of the Kidney Liver Muscle Kidney Liver Muscle 
carcasses 
Range of 76.7- 163.6-1708.0 178.1-1926.0 308.4-2819.0 240.8- 67.1-
oxytetracycline 2409.0 1824.0 1709.0 
residue  
f g e
Mean 1267.0 904.9±421.4   729.6±374.3   1436.0±554.1   761.7±375. 546.2 
 e f g
concentration ±476.4   6   ±373.8   
±SD(µg/kg) 
Samples 56.7 50.0 48.3 60.0 60.0 50.7 
positive for 
oxytetracyclin
e (%) n=60 
Samples with 31.7 40.0 46.7 40.0 41.7 45.0 
oxytetracyclin
e levels above 
MRLs (%) 
 e, f, g 
Superscripted values in columns are significantly different (p< 0.05). 
 
 
 
 
 
4.3.3.6 Prevalence of oxytetracycline residue in chicken samples from farms and
 markets in Lagos and Ibadan 
HPLC quantitative analysis of the chicken samples indicated oxytetracycline residue 
prevalence of 71.7 and 75.0% in liver and muscle respectively from Ibadan poultry farms, 
and also prevalence of 63.3 and 60.0% were obtained in liver and muscle respectively from 
Ibadan chicken market. Oxytetracycline residue prevalence from Lagos poultry farms were 
53.3 and 60.0% in liver and muscle respectively and also 41.7 and 56.7% prevalence in 
chicken liver and muscle respectively from Lagos market. The overall mean concentration of 
oxytetracycline residue obtained from chicken muscle and liver samples in this study were 
1042.0±122.8 and 615.0±91.8µg/kg respectively. The distribution of the mean residue levels 
in the chicken across the market and farm locations are shown in table 5.8 with a range of 
41.7 to 75.0% of the samples having oxytetracycline above the CAC MRLs (table 5.9). 
Chicken samples from Ibadan farms had the highest prevalence of the residue.  
 
 
 
 
 
 
 
 
 
Table 4.10: Oxytetracycline residue in chicken from Ibadan. 
Location Ibadan (farm) Ibadan (market) 
Portion of Liver Muscle Liver Muscle 
carcasses 
Range of oxytet 299-2481 164-1129 270-1911 183-1525 
residue (µg/kg)   
 i  i j  j
Mean concentration 1156  ±528  566.8 ±270.7  986.1 ±449.1 559.4 ±349  
±SD(µg/kg) 
Proportion of 
samples with 
detectable 
oxytetracycline 
residue (%) n=60 43 (71.7) 45 (75.0) 40 (63.3) 36 (60.0) 
Proportion with 
oxytetracycline 
above MRL 32 (53.3) 36 (60.0) 25 (41.7) 34 (56.7) 
 i, j 
Superscripted values in columns are significantly different (p< 0.05). 
 
 
 
 
 
 
 
Table 4.11: Oxytetracycline residue in chicken from Lagos 
Location Lagos (farm) Lagos (market) 
Portion of carcasses Liver Muscle Liver Musce 
Range concentration(µg/kg)   164-2674 231-1853 19-1901 48-1660 
 l  l  k  k
Mean concentration 1130 ±614.4  752.4 ±393.7  895.7 ±473.8  583.8 ±396  
±SD(µg/kg) 
Proportion of samples with 
detectable oxytetracycline 
residue (%) n=60 42 (70.0) 35 (58.3) 43 (71.7) 45 (75.0) 
Proportion with 
oxytetracycline above MRL 
(%) 34 (56.7) 35 (58.3) 31 (51.7) 36 (60.0) 
 l, k 
Superscripted values in columns are significantly different (p< 0.05). 
 
 
 
 
 
 
2500 
2000 
1500 
1000 
500 
0 
samples /location/season 
 
*Keys: 
 IbKW = Kidney wet/s (Ibadan), IbLW = Liver wet/s (Ibadan), IbMW = Muscle wet/s, (Ibadan) IbKD = Kidney dry/s 
(Ibadan), IbLD = Liver dry/s (Ibadan), IbMD = Muscle dry/s (Ibadan), IbCh Lmkt = chicken liver (Ibadan market), 
IbCh Mmkt= chicken muscle (Ibadan market),  IbCh Lfm  = chicken liver (Ibadan farm) IbCh Mfm = chicken muscle 
(Ibadan farm), LgCh Lmkt = chicken liver (Lagos market), LgCh Mmkt chicken muscle (Lagos market), LgCh Lfm  = 
chicken liver (Lagos farm), LgCh Mfm = chicken muscle (Lagos farm), LgKW= kidney wet/s (Lagos), LgLW = 
Liver wet/s (Lagos), LgMW= Muscle wet/s (Lagos), LgKD= kidney dry/s (Lagos),  LgLD= liver dry/s (Lagos), 
LgMD=muscle dry/s (Lagos), AkKW= Kidney wet/s (Akure), AkLW= Kidney wet/s (Akure), AkMW= Muscle 
wet/s, (Akure) AkKD = Kidney dry/s (Akure), AkLD = Liver dry/s (Akure), AkMD = Muscle dry/s 
Figure 4.5: Mean oxytetracycline residue levels in beef and chicken from southwest Nigeria. 
 
 
 
 
 
concentration (µg/kg)  
 
Figure 4.6: Seasonal prevalence of oxytetracycline residue in cattle 
 
 
 
 
 
 
 
 
 
 
 
 
4.3.4 Hypotheses testing 
Statistical analyses of antimicrobial residues prevalence in the meats types obtained by 
®
Premi Test across the different abattoirs and during the different seasons of the year were 
obtained by chi-square test. There was no significant difference (p<0.05) in the overall 
prevalence of antimicrobial residues across the three abattoirs but the overall residue 
prevalence of antimicrobial residues in chicken (69.1%) was significantly higher (p<0.05) 
than in beef (45.4%), therefore the null hypothesis (HO3) is rejected.  Also, the prevalence of 
antibiotic residues in beef during the wet season was significantly higher (p<0.05) than the 
prevalence during the dry season, hence the null hypothesis (HO4) is rejected.  
The mean oxyteracycline residue concentrations were analysed by ANOVA and Tukey's 
Multiple Comparison Test. There was no significant difference in the mean oxytetracycline 
residue concentration (p<0.05) in the different meat types across the different abattoirs, but 
the levels of oxytetracycline residue in beef during the wet season were significantly higher 
tha residue levels during the dry season (p<0.05) therefore, HO5 is rejected.  
The mean residue concentrations from in the chicken liver were significantly higher (p<0.05) 
than in the chicken muscle but there was no significant difference (p< 0.05) between the 
mean residue in chicken from farms and the markets within and across the cities. However, 
the mean concentration of oxytetracycline residue in chicken was significant higher (p< 0.05) 
than mean concentration in beef (HO6 is therefore rejected). 
The overall mean concentration of oxytetracycline residue levels obtained in bovine kidney, 
liver and beef were 1324.7±148.0, 856.6±118.0 and 651.7±101.3µg/kg were respectively 
were significantly higher (p<0.5) than the CAC recommended MRLs of 1200, 600 and 200 
µg/kg oxytetracycline in kidney, liver and muscle respectively (HO7 is therefore rejected).  
4.4 Discussion 
The extensive use of veterinary drugs in animal production resulting from gigantic growth 
and intensification of animal production in order to meet the increasing population demand 
for animal protein have become a major global public health concern (Botsoglou and 
Fletouris, 2001; Jafari et al., 2007). There are several national and international regulatory 
control and monitoring efforts to ensure safety of livestock products meant for human 
consumption. This study determined the prevalence of antimicrobial residues edible portions 
of cattle and chicken slaughtered for public consumption in three selected cities of southwest 
Nigeria. The results of this study showed higher prevalence in the samples of antimicrobial 
residue in both cattle and chicken than those obtained in previous studies by other workers in 
different parts of Nigeria. The total prevalence of 45.6% obtained in cattle and chicken 
samples respectively from this study were higher than 8.0, 7.4, 16.7 and 44.0% prevalence 
obtained by Oboegbulem and Fedelis, 1996; Kabir et al., 1999 and Dipeolu and Alonge, 
(2002) in slaughtered cattle respectively across the country. Also the 69.1% residue 
prevalence in chicken samples from the present study is higher than 33.1%, prevalence 
obtained by Kabir et al., (2004). While a recent study by Ezenduka et al., (2011) also 
reported 36.0 and 30% of commercial eggs from farms and retail outlets of Enugu, Nigeria 
positive for antibiotic residues respectively. 
The higher prevalence of antimicrobial residues obtained in the present study compared with 
the previous studies by other authors in Nigeria could be due to a better sensitivity of the test 
kit than the conventional overnight culture methods. Also the test organism (Bacillus 
®
stearothermophilus var. calidolactis) in Premi Test has been shown to be sensitive to wide 
range of antibiotics (Stead et al., 2004). This could account for the sensitivity as a broader 
screening method that was able to detect many of the antibiotics routinely used by livestock 
producers in the country. Stead et al., (2004) and Popelka et al., (2005) confirmed the broad 
®
spectrum and sensitivity of Premi Test with the ability to detect many antibiotic residues 
below MRLs. These authors also concluded that the assay will relieve the chemical analytical 
resources of food inspection laboratories and contribute to less positive animals, safer 
products and better consumer protection thereby assuring the quality of animal food products, 
which is beneficial for the consumers and the producers. More so, another great advantage of 
®
the Premi Test is the short time of the analysis (<4 hours) thereby ensuring quicker release of 
meat negative for antibiotics for public consumption unlike the conventional overnight 
microbial inhibition tests that were used by the previous author in Nigeria. Coupled with the 
®
ease of operation of the Premi Test, its sensitivity and the rapid results obtainable within 3 to 
4 hours the method is more practicable at all the levels of slaughter plants and slabs for 
antibiotics screening of large number of meat samples. 
Also, this study also showed that residue prevalence obtained in chicken was higher than in 
cattle. This may be as a result of more frequent administration of different antibiotic 
combinations simultaneously in feed and water in poultry than in cattle, since poultry are 
reared under intensive management system with more challenges of infections compared to 
cattle which are reared on semi-intensive and extensive management system. Dipeolu et al., 
(2005) also reported routine antibiotics dosing of chicken in the markets against stress and 
diseases until they are sold for the fear of economic loss due to mortalities. Dipeolu et al., 
(2005) also reported that eggs from medicated chickens are sold usually sold for public 
consumption because poultry farmers could not adhere to withdrawal periods of antibiotics 
for fear of economic losses.  
Nonga et al., (2009) also obtained a prevalence of 70.0% antibiotic residues in commercial 
broilers in Tanzania using microbial inhibition test while Muriuki et al., (2001); Shitandi and 
Sternejo (2001) detected 45.6% and 21.0%  prevalence in Kenyan beef and milk respectively. 
These results are comparable to high prevalence obtained in this study thereby indicating 
widespread of antibiotic residues in meat across developing countries as a result of 
indiscriminate use of antibiotics in these nations. This implied that the consumers were 
ingesting some level of antibiotics in food animal products which has significance public 
health consequences. 
Antimicrobial residue prevalence in the liver samples was the highest followed by kidney and 
lowest in the muscle. These results are consistent with the findings of several authors since 
the liver and kidney are the major organs of drug metabolism and excretion. Higher 
prevalence of residues were also obtained  in chicken than beef this could be due to increase 
frequency of use of more antibiotics in poultry for prophylaxis and as feed additives which 
were reared by intensive system than in the cattle by extensive management system. The 
higher prevalence of antibiotic residues obtained during the wet season than during the dry 
season. This could correlates to higher prevalence of bacterial diseases in the wet season 
requiring more antibiotics usage in wet season than the dry seasons. 
According to CAC and other national residue regulatory monitoring and surveillance 
programs, confirmation of the identity and concentration of tissue residues by chemical 
analysis are required to compared with the MRLs in order to quantitatively assess the residue 
risk.  
This study detected oxytetracycline from 56.2% and 64.2% of the meat samples from cattle 
®
and chicken that positive by Premi Test respectively in the study area. The results showed a 
higher prevalence than 45.6% obtained by Muriuki et al., (2001) in a survey of beef samples 
from Kenya slaughter. There has not been HPLC quantification of oxytetracycline residue in 
Nigerian meat. However, Dipeolu and Alonge, (2002) obtained tetracycline residue 
prevalence of 16.63, 15.0 and 13.34% in liver, kidney and muscles from Ogun and Lagos 
States (Nigeria) markets and 17.22, 16.11 and 6.67% of goat, cattle and pig meat containing 
streptomycin residue ranging from 0.06 to1.99µg/g from southwest (Dipeolu and Alonge 
(2002). While Ibrahim et al., (2010) obtained 44% total residue in beef of which 26% were 
oxytetracycline from Sokoto abattoir, also, Fagbamila et al., (2010) in a recent survey of 
commercial eggs in some part of northern Nigeria obtained 3.6% positive for antimicrobial 
residues with only 0.1% tested positive for tetracycline residue. These authors employed 
microbial inhibition method could not have detected protein bounded antibiotics in these 
tissues that required physicochemical extraction. More so, the size of zone of inhibition is 
determined by several factors such as the sensitivity of the test organism, inoculum size, pH 
of the medium.  MIT is prone to false positive and negative but it is good for screening large 
number of samples as the first line of action in residue monitoring and control. Therefore the 
higher prevalence obtained in this study could be due to the specificity and sensitivity of 
HPLC method employed in this work as validation.  
The residue concentrations vary with the meat types, the mean concentrations of 
1324.7±148.0, 856.6±118.0 and 651.7±101.3µg/kg were obtained in bovine kidney, liver and 
muscle were respectively and 1042.0±122.8 and 615.0±91.8µg/kg in chicken liver and 
muscle respectively. The mean residue levels obtained were higher than codex MRLs for 
each meat type (200, 600 and 1200 µg/kg for muscle, liver, and kidney). In a similar study 
Muriuki et al., (2001) reported mean oxytetracycline residues of 1380 µg/kg in kidneys, 1090 
µg/kg in liver and 790 µg/kg muscle of cattle in Kenya. Also in a survey conducted by Al-
Ghamdi et al., (2000) in Saudi Arabia showed that antibiotic residue were present in 69.7% 
of broiler and 60%) layer chicken samples. While Salehzadeh et al., (2006) also obtained 
oxytetracycline residues 95.55% of farms survey in Iran with 27.77%, 95.55% and 18.88% of 
muscle, liver and kidney samples containing residues of oxytetracycline above MRLs 
respectively using HPLC.  
These results indicate that a large proportion of cattle and chicken meat being slaughtered for 
human consumption in Nigeria and other developing countries contain varying detectable 
levels of oxytetracycline residue above MRLs which could result in public health hazards. 
Also the prospect of international trade in meat products envisage by most developing 
countries through WTO due to increase livestock production in this region cannot be 
achieved with such products that cannot meet Codex SPS standards. This implies a huge loss 
of potential foreign exchange. 
There is stringent regulation of drug use in food animals and residue control in developed 
countries with resultant low level of residue violation. Okerman et al., (1998b) reported that 
1.2% of chicken meat samples and 2.7% of pork meat samples, purchased from retail outlets 
contained residues belonging to the tetracycline family. De Wasch et al., (1998) reported that 
two out of 523 pork and none of the 1768 chicken samples containing oxytetracycline residue 
at levels higher the maximum residue limit, while Oka et al., (2001)  obtained the overall 
incidence of  30.9% tetracycline residues in beef and pork from Japan, while Nhiem et al., 
(2006) detected residue prevalence of 5.5% in pork from Vietnam. 
The results of this study also showed that the mean oxytetracycline levels were higher in liver 
and kidney than muscle, but the level in cattle muscle was higher than in chicken muscle. 
This could be due to the facts that cattle were administered with intramuscular injectable 
brands of the drugs while chicken were dosed through feed and water. However, there was no 
significance difference in the mean concentrations of oxytetracycline across the different 
locations and during the different climatic seasons. This could imply that there was no 
difference in livestock husbandry practices across the region and that oxytetracycline was 
commonly used throughout the year. 
 
 
CHAPTER FIVE 
ISOLATION AND ANTIBIOTICS SUSCEPTIBILITY OF ESCHERICHIA COLI 
O157:H7 FROM BEEF AND CHICKEN IN IBADAN AND LAGOS 
5.1 Introduction 
 There are growing concern of bacterial adaptation and evolution resulting in the emergence 
of a number of zoonotic microorganisms in the food and water.  Food-borne disease is a 
global public health concern. Mead et al., (1999) reported an estimated food-borne of 76 
million illnesses, 325,000 hospitalizations and 5,000 deaths annually in United States and in 
the United Kingdom, an estimated 2.37 million cases of food-borne gastroenteritis occurred 
in 1995 (Adak et al., 2002). Available data from United States Department of Agriculture 
Food Safety and Inspection Service (USDA-FSIS) indicated that 13 million kg of ground 
beef were contaminated with E. coli O157:H7 on August 12, 1997 and 9.5 million kg of beef 
trimmings and ground beef potentially contaminated with E. coli O157:H7 on July 19, 2002 
(Sofos, 2008). Escherichia coli is a widespread intestinal commensal organism found in 
human and animal resulting from faecal contamination or contamination during food animal 
slaughter it is often found in soil, water, feaces and foods.  
Shiga toxin-producing E. coli (STEC) O157:H7 has emerged as a major foodborne pathogen 
and a threat to public health following its initial identification in a 1982 outbreak of illness 
associated with the consumption of undercooked ground beef (Riley et al., 1983). There are 
many pathogenic strains causing a variety of illness in man and animals with associated 
clinical features and virulence factors depending on the serogroups from a food safety 
perspective, the EHEC groups are most important. Specifically, E. coli O157:H7 and O157: 
NM (non-motile) are recognized as major etiologic agents in hemorrhagic colitis (HC) and 
haemolytic-uremic syndrome (HUS) in humans (Thielman and Guerrant, 1999). As with 
other food-borne bacterial pathogens, the potential health hazard presented by foodborne E. 
coli is influenced by numerous factors, ranging from variations in farm-rearing practices and 
processing, storage, handling and cooking in the home (WHO, 2000). Cattle and other 
ruminants were identified as the main reservoir for human infections (Nataro and Kaper, 
1998; Gyles, 2007). Several outbreaks have been associated with other food commodities 
such as milk, lettuce and chicken (Rangel, et al., 2005). The bacteria is highly infectious for 
human being at a very low infectious dose of   10 to 100 organisms (Willshaw, et al., 1993) 
Antibiotics resistant E. coli has been reported over the past 50 years since the 
chemotherapeutic and growth promotion uses of antibiotics (Orden et al., 1999; Lambie et 
al., 2000). Studies in the UK found that, in the late 1950s, tetracycline resistance was already 
detectable in E. coli isolates from chickens and pigs fed rations containing less than 100 g 
tetracycline/ton (Smith, 1967). Resistance to other antibiotics was detected as new agents 
were introduced for therapeutic and growth promotion purposes (Smith, 1967; Anderson, 
1968). Antimicrobial resistant food-borne pathogens are acquired primarily through 
consumption of contaminated food of animal origin or water (Mead et al., 1999; National 
Research Council, 1998). Information on the magnitude of the public health burden due to 
resistant food-borne pathogens indicates that the situation is complex and differs by country. 
It is influenced by a number of variables such as antimicrobial use practices in farming, 
process control at slaughter, storage and distribution systems, the availability of clean water, 
and proper cooking and home hygiene, among others (WHO, 2000). The major concern on 
the public health threat of foodborne illness is infection by antimicrobial-resistant strains that 
lead to more intractable and severe diseases (Helms et al., 2002; Martin et al., 2004). This 
situation is further complicated by the potential of resistant bacteria to transfer their 
resistance determinants to resident comensals of the human microflora and other pathogenic 
bacteria. 
Several data have been published on resistance in E. coli originating from retail raw meat 
products (Meng and Doyles, 1997; Zhao et al., 2001), resistance to antibiotics is highly 
prevalent in bacterial isolates worldwide, particularly in developing countries including 
Nigeria (Hart and Kariuki, 1998; Aibinu et al., 2007; Okeke et al., 2005; Ojo et al., 2009). 
Unhygienic floor dressing of carcasses is a common practice in Nigeria resulting in carcass 
contamination and isolation of pathogenic microorganisms from meat and slaughtering 
facilities in Nigeria (Umolu et al., 2006, Ojo et al., 2009).  
Several countries of the developed nations have established national surveillance programmes 
whereby they continuously assess bacterial susceptibility to antimicrobials among zoonotic 
and commensal bacteria isolated from humans and animals. Such programs as Danish 
Integrated Antimicrobial Resistance Monitoring and Research Programme (DANMAP), 
Denmark; The National Antimicrobial Resistance Monitoring System (NARMS), USA; 
Japanese Veterinary Antimicrobial Resistance Monitoring System (JVARM), Japan; 
Monitoring Antimicrobial Resistance And Antibiotic Usage Animals, the Netherlands 
(MARAN);  Indian Initiative for Management of Antibiotic Resistance (IIMAR); Canada 
(CIPARS); Sweden (SVARM) and Norway (NORM-VET). 
However, there are no sufficient data on the susceptibility of zoonotic and commensal 
bacteria isolated from food animals and no national surveillance programmes on the 
antimicrobial susceptibility in Nigeria. The importance of resistance determinants derived 
from animals is still largely unknown and the the role of meat-borne bacteria as vectors in the 
transmission, spread and development of cross-resistance to several antibiotics requires 
critical scrutiny. White et al., (2004) suggested the need for continuous research on the 
ecology and epidemiology of major foodborne pathogens, and surveillance of retail food 
(including meat) products in order to characterize and mitigate food-borne bacterial 
resistance. Additionally, several authors emphasised the need for continuous assessment of 
the public health consequences of the use of antimicrobials in the animal husbandry (Smith et 
al., 2003; Hald et al., 2004; Phillips et al., 2004). Antimicrobial drug susceptibility profiles 
and genetic strain typing methods are useful epidemiologic tools to determine the sources of 
infections, including potential links between food animals and persons (Okeke et al., 2007). 
Considering the nature of veterinary drugs use in livestock and the prevalence of resistance 
pathogens in animal production and processing environment, this work was aimed at isolation 
and assessment the resistance patterns of meat-borne E. coli O15:H7 in beef and chickens 
processed for human consumption in Lagos and Ibadan, southwest Nigeria.   
5.2 Materials and Methods 
5.2.1 Sterilization of Glass Wares and Preparation of Culture Media 
All glass wares including petri dishes, Bijuo bottles, universal bottles, media bottles 
measuring cylinders, conical flask and others were thoroughly washed and rinsed with clean 
O
water and sterilised in the hot air oven at 160 C for 1hour before use.  
5.2.2 Preparation of microbiological media for bacterial isolation and identification:  
O
The culture media were sterilized by moist heat under pressure in the autoclave at 121 C for 
15 minutes and prepared according to manufacturers‟ recommendation. After sterilization by 
O
autoclaving, the solid media were allowed to cool to about 45 C in media bottles on the 
bench to cool and then about 20ml was poured into sterile covered petri dishes and were 
allowed to gel.  Air bubbles were removed from the surfaces of some of the agar plates before 
solidification and were kept in the refrigerator until they were to be inoculated. 
 
 
5.2.3 Samples and Sampling Procedures: 
One hundred samples (about 25grams) of beef were randomly obtained from Bodija and 
Oko-Oba abattoirs during the wet season and repeated in the dry season and also 100 samples 
each of broiler chicken meat were randomly and aseptically collected from Mokola slaughter 
market, Oko-Oba chicken slaughter market and poultry farms in Ibadan and Lagos (20 
samples from ten farms) shortly after meat dressing. The samples were obtained by carcass 
surface scrapings (excision method) with sterilised meat inspection knife and superficial 
2
cutting about 5cm  piece of tissue of about 3mm thick  from four different portions of each 
carcass, the knife was rinsed with about 100ml peptone water into sterile sample bags (Whirl-
Pak Nasco, USA). The sample bags were placed into icebox which was subsequently 
transported to the Food and Meat Hygiene Laboratory of the Department of Veterinary Public 
Health and Preventive Medicine, University of Ibadan for the bacteriology within 24hours. 
The samples were collected from April 2008 to June 2009.  
5.2.4 Bacterial isolation  
Each meat sample was thoroughly homogenised with 25ml peptone water and incubated 
o
overnight at 37 C.  A wire loop full of the broth culture was separately inoculated each onto 
® ®
7% sheep blood agar (Oxoid ) and MacConkey agar (Oxoid ). The plates were incubated 
aerobically at 37°C for 24hrs. The bacterial isolates were identified by their cultural 
characteristics, morphology, gram and biochemical reactions according to standard methods 
described by Barrow and Felthman (1993). Red to pink (lactose fermenters) colonies, Gram 
negative rod,  motile, indole positive, catalase positive, oxidase negative, and showed the 
standard biochemical characteristics of E. coli described by Barrow and Felthman (1993) 
were  further subcultured onto CT-Sorbitol-MacConkey (CT-SMAC) agar plates, and 
incubated at 37 °C at 24 hours. Colonies that were colourless to pale, flat and smooth, 
circular or serrated at the edge were selected as presumptive non-sorbitol fermenting E. coli 
for serological test. The bacterial isolates were identified by their cultural characteristics, 
morphology, Gram staining and biochemical reactions according to standard methods 
described by Barrow and Felthman (1993). 
5.2.5 Identification and Biochemical Tests 
a. Gram staining 
Sterile wire loop was used to pick a discrete colony of suspected E. coli from the agar plate 
onto a clean glass slide. The colony was emulsified in a small drop of normal saline and 
allowed to dry in the air. The smear was heat-fixed by passing over flame. The glass slides 
was labelled and arranged on a rack and were stained as follows: smears were flooded with 
methyl violent and allowed the stain to act for about 15 seconds. Excess stain was rinsed off 
with a little water. After which Gram‟s iodine was poured and allowed to act for about 15 
seconds which was washed off with water. This was followed by flooding with acetone 
which was almost immediately rinsed off under running water.  Subsequently safranin was 
poured and allowed to act for 30 seconds, washed off and dried by blotting paper. The stained 
smears were then examined under microscope with oil immersion using X100 objective lense 
(Barrow and Feltham, 1993). 
b. Haemolysis test 
Haemolytic activity of the isolates was tested by culturing the isolates in 7% sheep blood agar 
(Oxoid Columbia blood agar) and incubating at 37°C for 24 h. The isolates that produced 
haemolysis are presumptive EHEC and were further characterised. 
c. Catalase test 
Catalase test demonstrates production of catalase enzyme by the organism. Catalase releases 
oxygen from hydrogen peroxide. Members of the family Enterobactereacea including E. coli 
are catalase positive. Smear of suspected colony was put on a clean glass slide. And then a 
drop of 3% hydrogen peroxide was added and observed for effervescence after gently rocking 
the slide (Barrow and Feltham, 1993). 
d. Oxidase Test 
A redox dye (tetramethyl-P-phenydiamine) was added to a strip of filter paper and the culture 
of the colour of the filter paper from white to deep purple. E. coli and other members of the 
family Enterobactereacea are oxidase negative (Barrow and Feltham, 1993). This test 
demonstrates the presence of oxidase enzyme that catalyses the transport of electron between 
the bacterium and the dye. 
e. Motility Test 
 Motility was demonstrated by the hanging drop method according to Barrow and Feltham, 
(1993). Plasticine was made into a circle and placed on a cover slip; a drop of overnight 
culture of the organism in buffer peptone water was dropped at the centre of the circle. A 
microscope slide was placed on the plasticine and then inverted. This was viewed at X40 
objective under microscope. 
f. Indole Test  
Few drops of Kovac reagent (5 g  p-dimethylaminobenzaldehyde dissolved in mixture of 75 
ml amyl alcohol and 25 ml concentrated sulphuric acid) was added to a pure culture of the 
organism in peptone water. The mixture was shaken. The appearance of a pink or red ring 
layer at the upper surface of the mixture indicated positive result while the absence of the red 
ring indicated a negative result (Barrow and Feltham, 1993). 
g. Citrate utilization test 
Pure colony was inoculated into Simmon citrate agar according to Barrow and Feltham, 
o
(1993) in bijou bottles. These were incubated at 37 C for 18-24 hours citrate positive isolates 
changed the colour of the agar from green to blue while negative ones did not produce colour 
change. E. coli is citrate negative. 
h. Sugar fermentation test 
The appropriate sugar solution (1%) was prepared by dissolving 1g of the sugar in peptone 
water to which Andrade‟s indicator has been added (10ml of indicator/litre of peptone water). 
o
The sugar solution was dispensed into bijou bottle and sterilized in the autoclave at 121 C for 
5minutes. Bacterial isolates were inoculated into a set of sugar solution and incubated for 12-
o
18 hours at 37 C. Positive organisms that have fermented sugar changed the colour of the 
solution from colourless to pink while those that did not ferment sugar did not produce colour 
change.      
i. E. coli O157 latex agglutination test:  
®
This test was carried out using E. coli O157 latex agglutination test kit (Oxoid  DRO 120M, 
UK) according to the manufacturer‟s recommendation and protocol. The refrigerated reagent 
was allowed to thaw at room temperature before use. A drop of the test latex was dispensed at 
the edge of the circle on the reaction card provided. 2-3 loopfuls of saline was added to the 
center of the circle in both tests and control on reaction card. A portion of suspected colony 
was picked with a sterile stick and carefully emulsified in a saline drop. The mixing sticks 
provided was used to spread the mixture over the entire area of the ring the same was done 
with the control latex and control organism. The card was rocked in a circular motion while 
observing for visible agglutination within one minute by the test latex and identified as E. coli 
O157 while those with no agglutination were considered negative. Sorbitol-positive E. coli 
ATCC25922 was used as negative control. 
5.2.6 Determination of Antibiotic Susceptibility and resistance pattern of E. coli O157 
isolates 
 The E.coli O157 isolates were further tested for their susceptibility to antimicrobial agents 
by disc-diffusion method according to Bauer et al., (1966) and Cheesbrough, (2000). The 
isolates were screened for their susceptibility to some commonly used antibiotics using 
commercially available multo-disks purchased from Abtek Biological Ltd, England 
containing nitrofurantoin (200μg), cefuroxime (25μg), norfloxacin (30μg), cotrimoxazole 
(25μg), gentamycin (10μg), tetracycline (30 μg), ciprofloxacin (25μg), nalidixic acid (30μg), 
chloramphenicol (30μg) and ampicillin (25 μg) were used.   E. coli NCTC 10418 was used as 
positive control. About 3ml of overnight nutrient broth culture of the pure colonies was 
flooded on the surface of Nutrient agar plates while the excess is carefully discarded into 
disinfectant. The inoculated plates were allowed to dry for about 20 minutes. Subsequently, 
the antibiotic discs were carefully and aseptically placed on the surface of the agar. The plates 
O
were incubated at 37 C for 16-24 hours. Inhibitory zones of growth were observed, measured 
and recorded. The result was interpreted according to National Committee for Clinical 
Laboratory Standards (NCCLS) now known as Clinical Laboratory Standard Institute (CLSI) 
guideline, (2005). The ssusceptibility of the isolates was characterized according to the 
breakpoints recommended by the NCCLS and designated as susceptible, intermediate or 
resistant. Intermediate strains were grouped with the sensitive isolates. Zones of inhibition 
above 2mm were recorded as sensitive, while the discs with no inhibition or below 2mm were 
recorded as resistant. 
 
 
5.2.7 Statistical Analysis 
The positive results were express in percentages as prevalence rates for both beef and chicken 
meat. Statistical comparison of the prevalence rates and the frequencies of resistance among 
isolates obtained from different meat types and sources were obtained by chi-square (χ2) test.  
5.3 Results 
5.3.1 Prevalence of E. coli O157:H7 in Beef and Chicken 
Based on colonial morphology, microscopy and the biochemical tests E. coli were isolated 
from which E. coli O157:H7 serotype was confirmed with the agglutination test.  
Out of a total of 400 each of beef and chicken samples examined in this study 186 and 129 
isolates of E. coli were isolated from beef and of chicken respectively. Seventy nine (19.8%) 
and 58 (14.5%) of isolates were confirmed positive for E. coli O157:H7 serotype from beef 
and chicken respectively. The prevalence of this pathogen in the beef from Bodija 
metropolitan abattoir were 26% and 31% during dry and wet season respectively while beef 
from Oko-Oba yielded the prevalence of 10% and 12% during the dry and wet season 
respectively (table 5.1).  
Results of the chicken samples showed prevalence of 13% in Ibadan chicken slaughter 
markets, 18% in broiler from Ibadan farms, 14% in Lagos chicken slaughter market and 13% 
in chicken from Lagos farms (table 5.1). Beef from Bodija abattoir (Ibadan) had the highest 
contamination with this organism. Contamination was also highest in the meat obtained 
during the wet season than the dry season. 
The prevalence of E. coli O157 was significantly higher in beef (p<0.05) compared to 
chicken (19.8% vs. 14.5%).  The prevalence of beef at the Bodija abattoir is also significantly 
higher than that of Oko-Oba abattoir, Lagos (p<0.05).  
Table 5.1 Distribution of E. coli O157 isolated from beef and chicken 
Carcass type Sample location No of chicken No of NSF* (E. No of E. coli 
(season) samples (n) coli) isolated O157 isolated 
Cattle (beef) Bodija (dry s.) 100 45 26 
Bodija (wet s.) 100 63 31 
Oko-Oba (dry s.) 100 36 10 
Oko-Oba (wet s) 100 42 12 
Subtotal  400 186 79 
(46.5%) (19.8%) 
Chicken Ibadan (market) 100 38 13 
Ibadan (farms) 100 33 18 
Lagos (market) 100 36 14 
Lagos (farms) 100 22 13 
Subtotal 400 129 58 
(32.3%) (14.5%) 
Total 800 215 137 
(26.9%) (17.1%) 
 
 
 
 
 
 
 
 
5.3.2  Antibiotics susceptibility and resistance pattern of E. coli O157 isolates 
Antibiotic susceptibility profile showed that all the E. coli O157 isolates from beef and 
chicken were resistant to one or multiple antibiotics. The frequencies of resistance by the 
isolates from beef and chicken to the individual antibiotic are shown in table 5.2 and 5.3 
respectively. The isolates exhibited resistance to all the antibiotics with tetracycline resistance   
(91.1 and 89.7% in beef and chicken respectively) being the highest. Nine different resistant 
patterns were identified with the isolates from chicken and beef as shown on tables 5.4 and 
5.5 
 
 
 
 
 
 
 
 
 
 
 
 
Table 5.2: Frequencies of Antibiotics Resistant E. coli O157:H7 isolates from Beef 
Antibiotics No of resistant Distribution of resistant isolates 
isolates 
(prevalence %) Bodija (d. Bodija (w. Oko-Oba (d. Oko-Oba 
season) season) season) (w. 
saeson) 
Ampicillin 18 (22.8) 8 4 3 3 
Cefuroxime 40 (50.6) 12 18 4 6 
Ciprofloxacin 6 (7.6) 1 1 2 1 
Chloramphenicol 20 (25.3) 7 9 2 2 
Cotrimoxazole 15 (19.0) 7 5 2 2 
Gentamycin 12 (15.2) 5 4 1 2 
Nalidixic 8 (7.6) 3 2 1 2 
Nitrofurantoin 60 (80.0) 18 23 8 11 
Norfloxacin  15 (19.0) 18 25 9 8 
Tetracycline 72 (91.1) 24 29 9 10 
 
 
 
 
 
 
 
 
Table 5.3: Frequencies of antibiotics resistant E. coli O157:H7 isolates from chicken 
Antibiotics No of resistant Source of isolates 
isolates (%) 
Ibadan Ibadan Lagos Lagos 
market farm market farm 
Ampicillin 16 (27.6) 5 3 3 5 
Cefuroxime 35 (60.3) 8 8 9 10 
Ciprofloxacin 10(17.2) 2 4 2 2 
Chloramphenicol 30 (51.7) 7 11 6 6 
Cotrimoxazole 16 (27.6) 5 4 3 4 
Gentamycin 15 (25.9) 2 6 3 4 
Nalidixic 8 (13.8) 2 1 2 3 
Nitrofurantoin 45 (80.8) 8 14 10 13 
Norfloxacin  17 (29.3) 3 6 3 5 
Tetracycline 52 (89.7) 12 17 12 11 
 
 
 
 
 
 
 
 
Table 5.4: Antibiotic resistance patterns of E. coli O157:H7 isolated from beef from
  Lagos and Ibadan abattoirs 
Pattern of resistance Isolates from beef 
Bodija (dry s.) Bodija (wet s.) Oko-Oba (dry Oko-Oba (wet 
s.) s.) 
Am,C,Cf,Co,Gn 4 6 2 0 
Na,Nf,Te 
Am,C,Cf,Co,Gn,N,Te 3 5 0 3 
Am,C,Cf,N,Na,Te 5 3 0 3 
Am,C,Cf,Cp,N,Te 3 2 2 0 
Am,C,Co,N,Te 0 5 0 2 
Am,C,N,Te 2 3 1 1 
Am,C,Cf,N 1 0 3 0 
N,Cp,Nf,Te 2 4 0 2 
Te 6 3 2 1 
Total 26 31 10 12 
 
 
 
 
 
 
 
 
Table 5.5: Antibiotic resistance patterns of E. coli O157:H7 isolated from chicken
  from Lagos and Ibadan markets and farms 
Pattern of resistance Isolates from chicken 
Ibadan Ibadan Lagos Lagos 
chicken chicken chicken chicken 
(market) (farms) (market) (farms) 
Am,C,Cf,Co,Gn Na,Nf,Te 4  1 3 
Am,C,Cf,Co,Gn,N,Te 0 1 1 2 
Am,C,Cf,N,Na,Te 2 0 2 0 
C,Cf,Cp,N,Te 0 2 0 2 
Am,C,Co, Gn,N,Te 3 3 3 4 
Am,C,N,Te 0 2 6 2 
Am,C,Cf,N 2 3 2 0 
N,Cp,Nf,Te 1 0 0 1 
Te 1 4 2 1 
Total 13 18 14 15 
 
 
 
5.4 Discussion 
E. coli is one of the common microflora of gastrointestinal tract of human being and animals 
including poultry but may become pathogenic to both (Jawetz et al., 1984; Fairbrother and 
Nadeau, 2006). Although most isolates of E. coli are usually non-pathogenic but they are 
considered as indicators of faecal contamination in food. It is use as an indicator bacterium 
because it acquires antimicrobial resistance faster than other conventional bacteria and 
transferred to pathogenic bacteria (Von Baum and Marre, 2005; Miranda et al., 2008). E. coli 
O157:H7 or Shiga toxin producing E. coli (STEC) is a major cause of food borne disease 
globally (Armstrong et al., 1996). 
This study demonstrated a high prevalence of E. coli contamination of beef and chicken from 
which the pathogenic   E. coli O157:H7. The high prevalence of contamination of meat from 
the different abattoirs and slaughter houses shown in this study is an indication organism for 
the presence of unacceptable contamination with bacteria. Seasonal prevalence of the 
contamination also showed significantly higher prevalence of the organism contamination 
during the wet season than in the dry season at the different abattoirs. This could be as a 
result from higher proliferation of the organisms and poor hygiene during the wet season. 
Also the prevalence of the isolates was higher in cattle than in chicken could have resulted 
from better hygiene practices at poultry slaughter houses than those practiced at the cattle 
abbatoirs. The high level of carcass contamination  obtained in this study could be due to 
unhygienic slaughtering and meat processing engaged in these abattoir and slabs, where 
butchering of meat were done on concrete floor with inadequate basic slaughtering facilities 
including lack of potable water (Abiola, 1995). Also lack of the practice of hazard analysis 
critical control programme during the slaughtering process could have predisposed the 
carcasses to much contamination and subsequently the meats with multi resistant E. coli and 
other pathogens (Turtura et al., 1990; Umolu et al., 2006).  
The study also confirmed that food animals are the major reservoirs of E. coli O157:H7 
which could possess antimicrobial resistant genes that contaminate meat and milk meant for 
public consumption. The bacterium have also been isolated from live cattle, meat and milk 
from other parts of the country by different researchers (Ojo et al., 2009; Aibinu et al., 2007; 
Luga et al., 2007).  Umolu et al., (2006) isolated multiple resistant strains of E.coli in meat 
from slaughtered cattle in Edo State Nigeria while Aibinu et al., (2007) also isolated E. coli 
O157 from cattle, pig, chicken sheep and humans in Lagos and Ogun States. Daini and 
Adesemowo, (2008) also found the resistance of E. coli from Nigeria in 54% and 88% strains 
against gentamicin and tetracycline respectively. Also high resistance of enterotoxigenic E. 
coli has been reported by other authors across the globe. For example in England and Wales 
up to third isolated E. coli from pigs were multi-resistant (Mazel and Davis, 1998). In Canada 
almost all (93%) of tested isolates were resistant to tetracycline, and a similar number (91%) 
were resistant to sulphonamides. 
Contamination of meat and other animal products with entero-pathogenic bacteria and their 
contribution in the epidemiology of antibiotic resistant in man and animal are of global food 
safety concern (White et al., 1998). Most of the isolates obtained in this study were resistant 
to multiple antibiotics with variable resistance patterns.  The multiple antimicrobial 
resistances and the highest resistance to tetracycline obtained in this study were similar to the 
patterns obtained by Aibinu et al., (2007) who obtained 94.4% resistant tetracycline strains of 
E. coli O157:H7isolated from animals and man. This could be due to the high frequencies of 
use of tetracycline among livestock in Nigeria as growth promoter for routine 
chemoprophylaxis. Tetracycline are readily available in different dosage forms and in 
combination with other antibiotics and vitamins and accessible to livestock producers.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
This study also confirms the widespread resistance to most commonly used antimicrobial 
agents in both human and animal health practice in Nigeria. The public health significance of 
these findings is that antimicrobial resistant bacteria from food animals may colonize the 
human population via the food chain, contact through occupational exposure, or waste runoff 
from meat production facilities to the neighbourhood.  
The multiple antibiotic resistance partterns exhibited by all the isolates  obtained in this study 
is similar to the findings from Nigeria and other parts of the world (Rahman et al., 2001; 
Khan et al., 2002 Zhao et al., 2005; Umolu et al., 2006;  Aibinu et al., 2007; Ojo et al., 
2009;). Antimicrobial use and/ or especially abuse have been considered to be the most vital 
selecting force to antimicrobial resistance of bacteria (Okeke et al., 1999). There are well 
established evidence that antibiotics can lead to the emergence and dissemination of resistant 
E. coli which can then be passed into people via food or direct contact with infected animals. 
These resistant microbes also function as a potential source in the transportation of 
antimicrobial resistance to human pathogens (Van de Bogaard et al., 2001; Schroeder et al., 
2002). The high prevalence of antibiotic resistant bacteria in this study as obtained from other 
developing countries has been associated with several factors including indiscriminate and 
uncontrolled use due to unregulated access of non-professional to different classes of 
antimicrobial over-the-counter (Dina and Arowolo, 1991; Hart and Kariuki, 1998; Okeke et 
al., 1999). Selective pressures exerted by unregulated use of antibiotics as a growth promoter 
in food animals have created large reservoirs of transferable antibiotic resistance in the 
ecosystem and to bacterial pathogens of humans (Witte, 1998). These antibiotic resistant 
strains can ultimately replace the drug sensitive microorganisms from antibiotic saturated 
environment (Van de Boogard and Stobberingh, 2000). 
  
This study revealed that retail raw meats are often contaminated with food-borne pathogens in 
variable prevalence and antibiotic resistance patterns; thereby stressing the need for prudent 
and regulated use of antimicrobial in food animals, increased implementation of hazard 
  
analysis of critical control point (HACCP) and consumer food safety education efforts. 
CHAPTER SIX 
CONLUSIONS AND RECOMMENDATIONS 
6.1 Conclusions 
The findings in this study elucidated the importance of antibiotics usage in cattle and poultry 
and provided the quantitative analysis of the prevalence and levels of antimicrobial residues 
and E. coli O157:H7 contamination in beef and chicken meat being consumed in cities of 
south western Nigeria. The pathogens could have been carried over along production and 
meat processing line water troughs have been shown to support E. coli O157, and be a source 
of colonisation.  
The widespread and unrestricted usage of different antibiotics in food animals without 
adequate diagnosis, prescription and supervision by veterinarians contribute greatly to the 
selective pressure on microorganisms and resulting in multiple resistant strains of bacteria 
and the deposit of residues of these drugs in the meat. This was evident by the high 
prevalence of resistance E. coli O157:H7 and antibiotic residues in the meat. Also the 
common practices of unhygienic meat processing and floor dressing of carcasses predisposed 
the meat to contamination by both the flora and pathogenic bacteria such as the E. coli 
O157:H7. 
The multiple drug resistance patterns exhibited in this study is of public health importance as 
E. coli generally is a common bacterial flora of humans and animals that carries transmissible 
plasmids that enhance and maintain the dissemination of antibiotic resistance genes among 
other pathogenic and commensal bacteria. In addition the risks of intestinal and extra-
intestinal infections of consumers with the resistant E. coli O157:H7 from the contaminated 
could account for the incidence of renal failure among hospitalised patient in Nigeria. 
Tetracycline resistance was the most common resistance among the pathogen in this study 
could have resulted from the drug being one of the most commonly used antibiotics in animal 
production. Different brands of tetracycline were reported being administered orally in feeds 
and water or by injection to both cattle and poultry.   
This study also provided quantitative data on the prevalence of oxytetracycline residue in 
cattle and chicken meat that were being consumed in cities of southwest Nigeria.  The results 
of this study revealed that greater proportion of the meat being consumed in southwest 
Nigerian cities contained oxytetracycline residues above international food safety standards. 
The meat could also contain residues of several other antibiotics that are available for use in 
livestock. The high proportion of cattle and chicken meat samples containing residues of 
antimicrobials could be due to the misuse and lack of strict regulation and control of 
antimicrobial use Nigeria livestock production. This therefore requires urgent public health 
attention by the consumers and appropriate regulatory agencies in the country. More so, 
Nigeria being a member of WTO has the potential of participating in international meat and 
other livestock trade that could increase foreign earning if appropriate SPS measures are 
observed to regulate the industry. 
6.2 Contributions to Knowledge 
a. This work demonstrated the inadequate structure, practice and lack of awareness of 
food safety objective in food animal production among livestock producers in 
southwest Nigeria and the unregulated practices of animal heath management. 
b. Another major contribution of this work is that it is the first quantitative prevalence 
analysis of oxytetracycline residue in meat in Nigeria using HPLC analytical method 
comparable with international food safety regulation (CAC) protocols for 
confirmation of violative levels of residue. This study showed that high proportion 
(37.8 to58.8%) of beef and chicken being consumed in southwest Nigerian cities 
contained antimicrobial residues especially oxytetracycline residues above the codex 
maimum residue limits (MRLs). 
c. E. coli that is generally considered a conmensal has been assuming pathogenic status 
also of major role in the dissemination of antibiotic resistance genes, this work 
elucidate the prevalence and antibiotic resistance status of the highly pathogenic 
E.coli O157:H7 contamination of beef and chicken sold for human consumption in 
the southwest Nigeria. This work also attempted to associate the high prevalence of 
resistant STEC of tetracycline and residue of oxytetracycline in chicken and beef with 
the indiscriminate usage of antibiotics among the livestock farmers. 
 
 
 
 
 
 
 
 
 
 
 
6.3 Recommendations 
Food animals and foods of animal origin are traded worldwide and the occurrence of 
antimicrobial resistance is a global problem. Programmes monitoring the occurrence and 
development of resistance and consumption of antimicrobial agents are strongly desirable. It 
is recommended that large scale epidemiological survey covering all the regions in Nigeria be 
carried out to fully evaluate the consumer safety of food animal products (meat, milk and 
egg) concerning resistant food-borne pathogens and antibiotic residues in the country.  
According to WHO, global initiatives and the establishment of common guidelines and 
systems controlling resistance in all countries must pay closer attention to the national 
monitoring of distribution, prescription and usage in the developing countries (including 
Nigeria). There is need for establishment of national pharmaco-epidemiological surveillance 
program on antibiotic usage, residues and resistant food-borne pathogens in man and animal, 
especially along the food chain to protect meat consumers Nigeria. 
Application of HACCP from farm to fork in food animals and meat production and 
processing is also recommended to monitor and control chemical and microbial hazards along 
the food chain. This should involve proper structuring of livestock production in the country, 
regular extension education for livestock producers, marketers and processors on good animal 
husbandry practice to ensure safe animal protein supply.  
Veterinary supervision of livestock production for proper diseases diagnosis, prescription of 
antibiotics and observance of withdrawal period in food animal production in Nigeria are 
equally recommended. Good management practices and vaccinations of livestock as 
alternatives to antibiotic prophylaxis are also recommended. Vaccination of poultry has been 
very effective in reducing the incidence of food-borne pathogens among livestock.  The 
feeding of probiotics (“beneficial bacteria”) to livestock to competitively exclude the 
pathogens is also recommended as a good alternative to antibiotic chemotherapy.  
Hygienic meat production and processing practices should be promoted among the butchers 
and other meat handlers. The improvement of abattoir facilities to include laboratory 
infrastructure for routine testing or monitoring of food-borne microbial and chemical hazards 
is also recommended. This involve establishment of modern abattoirs meat storage and 
supply chain with potable water.  Adequate water treatment such as chlorination will help to 
reduce the incidence E. coli in livestock farms and abattoir water. 
Rapid residue screening kits such as Premi®Test should be made available at the meat 
inspection laboratories. Establishment of reference laboratories within the Local Government 
Areas, States and Regions of the countries is also recommended for confirmation of chemical 
and microbial safety of food of animal origin. These will greatly enhance Nigeria‟s 
participation in international meat trade and boost our foreign investment. 
There is also the need to review and amend the enabling laws on animal disease control, 
handling of veterinary drugs and meat inspection in Nigeria to ensure safety of meat 
consumers.  There is need to create Veterinary Directorate at National Directorate for Food 
and Drug Administration and Control to function like the Centre for Veterinary Medicine of 
FDA and EUCVM. There must also be stricter regulations and enforcement on the use of 
antibiotics accompanied by strategies to educate the public, physcians, and veterinarians on 
the appropriate use of antibiotics. 
 Pharmaco-epidemiological studies are required on safety of food of animal origin 
through molecular tracking of food-borne pathogens, the mobility and transfer of antibiotic 
resistance genes (markers) along the food chain. There is also the need for national 
quantitative risks surveillance of meat, milk, egg and honey for residues of antibiotics and 
other growth promoters which are inimical to public health are highly desired.  The true 
impact of antibiotic use as growth promoters need to be accessed since antibiotic resistance 
and residues are important factors in international livestock trade between different countries 
of the world and human migrations. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
REFERENCES 
Aalback B, Rasmussen J, Nielsen B & Olsen JE (1991) Prevalence of antibiotic-resistant 
Escherichia coli in Danish pigs and cattle. APMIS 99, 1103-1110. 
Aarestrup F.M. (2005). Veterinary drug usage and antimicrobial resistance in bacteria of 
animal origin. Basic Clin Pharmacol Toxicol 96:271-281. 
Aarestrup, F.M. (1999). Association between the consumption of antimicrobial agents in 
animal husbandry and the occurrence of resistant bacteria among food animals. Int J 
Antimicrob Agents12:279-85. 
 Aarestrup, F.M. (2000). Characterization of glycopeptide-resistant Enterococcus faecium 
(GRE) from broilers and pigs in Denmark: genetic evidence that persistence of GRE 
in pig herds is associated with coselection by resistance to macrolides. Jour Clin 
Microbiol 38:2774–2777. 
Aarestrup, F.M., Nielson, E.M., Madsen M., Engberg J. (1997). Antimicrobial susceptibility 
patterns of thermophilic campylobacter species from humans, pigs, cattle, and broilers 
in Denmark. Antimicrob Agents Chemother 41: 2244-2250. 
Abiola, S. S. (1995). Assessment of abattoir and slaughter slab operation in Oyo State. Nig. J. 
of Ani. Prod 5: 54-62.   
Abraham, E.P. and Chain, E. (1940). An Enzyme from Bacteria able to destroy Penicillin. 
Nature. 146: 837-840. 
Abraham, E.P., Chain, E., Fletcher, C.M., Gardner, A.D., Heatiey, N.G., Jennings, M. A. and 
Florey, H.W. (1941). Further observations on penicillin Lancet II 177-89. 
Adak,G.K., Long,S.M. and O'Brien,S.J. (2002). Trends in indigenous foodborne disease and 
deaths, England and Wales: 1992 to 2000. Gut 51:832-841. 
Adesiyun, A.A. and Kaminjolo, J.S. (1992). Susceptibility to antibiotics of Escherichia coli 
strains isolated from diarrhoeic and non-diarrhoeic livestock in Trinidad. Revue Elev 
Med Vet Pays Trop 45: 260-262. 
Aerts, M.M.L., Hogenboom A.C., Brinkman U.A. (1995). Analytical strategies for the 
screening of veterinary drugs and their residues in edible products. J. Chromatogr B: 
Biomed Sci Appl 667:1-40. 
Agwuh, K. N. and Alasdair MacGowan, A. (2006). Pharmacokinetics and pharmacodynamics 
of the tetracyclines including glycylcyclines. J.  Antimicrob Chemother. 58: 256–265 
Aibinu, I.E., Peters R.F., Amisu K.O., Adesida S.A., Ojo M.O. and Odugbemi T. (2007). 
Multidrug Resistance in E. coli O157 Strains and Public Health Implication. J. Am. 
Sci. 3:22-33. 
Alabi, R.A. and Isah, A.O. (2002). Poultry production constraints: The case of Esan West 
L.G.A. of Edo State, Nigeria. African Journal of Livestock Extension 1:58–61. 
Alanis, A. J. (2005).  Resistance to antibiotic: Are we in the post-antibiotic era? Archives 
Medical Research 36: 69-75. 
Al-Ghamdi, M.S., Al-Mustafa, Z.H., Al-Faky,A., El-morsy,I.H.and H. Essan, (2000). 
Residue of tetracycline compound in eastern province of Saudi Arabia. Public Health 
114: 300-304. 
Aliu, Y.O. (2004). Veterinary Residues in Nigeria‟s Food. Presentation at National 
Awareness Training Programme on Food Contaminants and Residues: organized by 
National Agency for Food and Drug Administration Control (NAFDAC) on May 6-7 
2004, Lagos Nigeria.. 
Al-Mustafa, Z.H., and Al-Ghamdi, M.S. (2002). Use of antibiotics in the poultry industry in 
Saudi Arabia: implications for public health. Ann Saudi Med 22:4-7. 
nd
Alonge, D. O. (2005). Textbook of meat hygiene in the tropics. 2  ed. Farmcoe press, Ibadan 
58Pp. 
Anderson, E.S. (1968). Drug Resistance in Salmonella typhimurium and its Implications. Brit 
Med J 3:333-339 
Armstrong, G.L., Hollingsworth, J. Morris, J.G. (1996). Emerging foodborne pathogens: 
Escherichia coli O157:H7 as a model of entry of a new pathogen into the food supply 
of the developed world. Epidemiol Rev 18:29-51.  
Bager, F., Aarestrup, F.M., Madsen, M. and Wegener, H.C. (1999). Levels of glycopeptide 
resistant E. faecium in broilers and pigs following ban on the use of avoparcin. 
Microbial Drug Resistance 5, 53-56. 
Barrow, G.T, Feltham, R.K.A. (1993). Cowan and Steel's Manual for the Identification of 
medical bacteria, 3rd ed. Cambridge University Press, Cambridge pp331. 
Bates, J, Jordens, J.Z. and Griffiths, D.T. (1994). Farm animals as a putative reservoir for 
vancomycin-resistant enterococcal infection in man. J Antimicrob Chemother; 34: 
507-14. 
Bauer, A.W. Kirby, W.M.M., Sherries, J.C. and Turck, M. (1966). Antibiotic Susceptibility 
Testing by a Standardized Single Disk Method. Amer J Clin Pathol 36:493-96. 
Bennet, J. and Bentley, R. (1989). What is a name? Microbial Secondary Metabolism. Adv. 
Appl. Microbiology 34:1-5. 
Berends B. R., Van Den Bogaard A.E.J.M., Van Knapen F., Snijders J. M.A. (2001). Human 
health hazards associated with the administration of antimicrobials to slaughter 
animals. Part II. An assessment of the risks of resistant bacteria in pigs and pork. Vet. 
Quarterly 23:10–21 
Berg, D.E., and Howe, M.M. (1989). Mobile DNA. Washington D.C. American Society for 
Microbiology  pp972. 
Bett, B., Machila, N., Gathura, P.B., McDermott, J.J. and Eisler, M.C. (2004). 
Characterisation of shops selling veterinary medicines in a tsetse-infested area of 
Kenya. Preventive Veterinary Medicine 63:29-38 
Black W.D. and Gentry, R.D. (1984). The Distribution of Oxytetracycline in the Tissues of 
SwineFollowing a Single Oral Dose. Can Vet J 25:158-161. 
Blanco, J.E., Blanco, M., Mora, A. and Blanco, J. (1997). Prevalence of bacterial resistance 
to quinolones and other antimicrobials among avian Escherichia coli strains isolated 
from septicemic and healthy chickens in Spain. J Clin. Microbiol 35:2184-2185. 
Blench, R.M. (1999). The Nigerian National Livestock Resource Survey: a personal account. 
In C. Baroin and J. Boutrais, eds. L'Homme et l'animale dans le Bassin du Lac Tchad, 
p. 627-648. Paris, IRD. 
Blench, R.M. and Marriage, Z. (1999). Climatic uncertainty and natural resource policy: 
What should the role of government be? Natural Resource Briefing Paper No. 31. 
London, Overseas Development Institute. www.oneworld.org/odi/nrp/31.html 
Boisseau, J. (1993). Basis for the evaluation of the microbiological risks due to veterinary 
drug residues in food. Vet. Microbiol. 35:187-192. 
Botsoglou, N.A., Fletouris, D.J. (2001). Drug Residues in Foods: Pharmacology, Food 
st
Safety, and Analysis. Marcel Dekker, 1  Ed. New York 961p. 
Butaye, P. (2000). Antimicrobial growth-promoters: a review of the products and related 
resistance problems. In Antimicrobial resistance in Enterococcus faecium and 
Enterococcus faecalis strains from animals and animal-derived foods. I. pp. 15-52. 
PhD thesis, Ghent University, Belgium. 
Butaye, P. Devriese, L.A. and  Haesebrouck, F. (1998). Effects of Different Test Conditions 
on MICs of Food Animal Growth-Promoting Antibacterial Agents for Enterococci. J 
Clin Microbiol 38(7):1907-1911. 
CAC - Codex Alimentarius Commission, (1999). Recommended methods of sampling for the 
determination of pesticide residues for compliance with MRLs CAC/GL 33-1999: 
Pp20 www.codexalimentariusnet.com  
CAC- Codex Alimentarius Commission, (2006). Joint FAO/WHO Food Standards 
Programme Codex Alimentarius Commission 29th Session Report of the Sixteenth 
Session of the Codex Committee On Residues Of Veterinary Drugs In Foods Cancun, 
Mexico, 8-12 May 2006 
CAC. (2009). Codex Alimentarius Commission Maximum Residue Limits for Veterinary 
Drugs in Foods. Updated as at the 32nd Session of the Codex Alimentarius 
Commission (July 2009). CAC/MRL 02-2009  1-36 
Cannavan, A. (2005). The development of strategies for the effective monitoring of 
veterinary drug residues in livestock and livestock products in developing countries. 
In: Book of abstracts of 2nd International Symposium on Recent Advances in Food 
Analysis, Prague, Czech Republic, 2-4 November 2005, p 170. 
Caputo, G.M., Applebaum, P.C. and Liu, K.K. (1993): Infections due to Penicillin Resistant 
Pneumococci: Clinical Epidemiologic and Microbiologic Features. Arch. Intern. Med. 
153: 1301–1310. 
Carattoli, A. (2001). Importance of integrons in the diffusion of resistance. Veterinary 
Resistance 32:243–259. 
Carman, R. J., van Tassell, R. L. and Wilkins, T. D. (1993). The normal intestinal microflora: 
ecology, variability and stability. Vet. Human Toxicol. 35:11-14. 
Catry, B., Laevens, H., Devriese, L. A., Opsomer G. and De Kruif A. (2003). Antimicrobial 
resistance in livestock. J. Vet. Pharmacol. Therap. 26: 81–93. 
CCFH (Codex Committee on Food Hygiene), (1993). Antimicrobial resistant bacteria in 
food. Codex Guidelines for the Establishment of a Regulatory Programme for Control 
of Veterinary Drug Residues in Foods. CAC/GL 16-1993.  
ftp://ftp.fao.org/codex/standard/volume3/en/gl_016e.pdf 
Cerf, O., Carpentier, B. and Sanders, P. (2010) Test for determining in-use concentration of 
antibiotics and disinfectants are based on entirely different concepts: “Resistance” has 
different meanings. Int J Food Microbiol 136:247–254 
Cerniglia, C.E. and Kotarski, S. (1999). Evaluation of veterinary drug residues in food for 
their potential to affect human intestinal microflora. Regul. Toxicol. Pharmacol 
29:238-261. 
Cheesbrough, M. (2000). Microbiological test In: District laboratory practice in tropical 
countries. Part 2.Cambridge: Cambridge University Press Pp 434.  
Chima J.C., Ogbogu, D.A. (1998). Chronic fowl typhoid infection in a commercial poultry 
farm. Nigerian Vet. J. 19: 1-4. 
Chiu, C.-H., T.-L. Wu, L.-H. Su, C. Chu, J.-H. Chia, A.-J. Kuo, M.-S. Chien, and T.-Y. Lin. 
(2002). The emergence in Taiwan of fluoroquinolone resistance in Salmonella 
enterica serotype Choleraesuis. N. Engl. J. Med 346:413–419. 
Chopra, I. and Roberts, M. (2001). Tetracycline Antibiotics: Mode of Action, Applications, 
Molecular Biology, and Epidemiology of Bacterial Resistance. Microbiol Mol Biol 
Rev 65: 232-260. 
Chopra, I., P. M. Hawkey, and M. Hinton. (1992). Tetracyclines, molecular and clinical 
aspects. J. Antimicrob. Chemother. 29:245-277. 
Clinical and Laboratory Standards Institute Performance Standards for Antimicrobial 
Susceptibility Testing- CLSI (2005). Performance standards for antimicrobial 
susceptibility testing; 15th informational supplement. CLSI/NCCLS M100–S15. 
Clinical and Laboratory Standards Institute, Wayne, PA. 
Codex Committee on Residues of Veterinary Drugs in Foods (2001). Discussion Paper on 
Antimicrobial Resistance and the Use of Antimicrobials in Animal Production, 13th 
Session, 4–7 December. CX/RVDF 01/10. Joint FAO/WHO Food Standards 
Programme, Charleston, SC. 
 Committee on Drug Use in Food Animals (1999). The use of drugs in food animals: benefits 
and risks. Based on reports commissioned by the Panel on Animal Health, Food 
Safety, and Public Health (a joint activity of the [USA] National Research Council 
and the [USA] Institute of Medicine. Wallingford, UK: CABI Publishing, and 
Washington, DC: National Academy Press. 290 pp. 
Concordet, D. and Toutain, P. L. (1997). The withdrawal time estimation of veterinary drugs: 
a non-parametric approach. J. Vet. Pharmacol. Therap. 20: 374-379. 
Corpet, D. E. (1993). An evaluation of methods to assess the effect of antimicrobial residues 
on the human gut flora. Vet. Microbiol 35: 199-212. 
Corpet, D.E and Brugere, H.B. (1996). Antimicrobial drugs in foods. Evakuation of the no 
effect on human microfloras recent Ris devel. Antimicrob. Agents and chemother 
1:113-123 
Courvalin, P. (1994). Transfer of antibiotic resistance genes between gram-positive and 
gram-negative bacteria. Antimicrob. Agents Chemother. 38:1447-1451 
CVMP (1995). Committee for Veterinary Medicinal Products. Note for Guidance: Approach 
towards Harmonisation of Withdrawal Periods. EMEA/CVMP, 036/95. EMEA 
website (http://www.emea.eu.int/index/indexv1.htm). 3.4.2004. 
CVMP (2001a). Revised guidance on pre-authorisation studies to assess the potential impact 
of veterinary medicinal products to antimicrobial resistance. EMEA/CVMP, 244/01. 
http://www.emea.eu.int/index/indexv1.htm (accessed on 12.5.2008). 
CVMP (2001b). Revised guideline on safety evaluation of antimicrobial substances regarding 
the effects on human gut flora. EMEA/CVMP, 234/01. EMEA website 
(http://www.emea.eu.int/index/indexv1.htm). (accessed on 12.5.2008). 
Daini O.A., Adesemowo A. (2008). Antimicrobial Susceptibility Pattern and R- Plasmids of 
Clinical Strains of Escherichia coli. Aus. J. Basic and Applied Sci. 2(3): 397-400. 
Daini, O.A., Ogbolu, D.O., Ogunledun, A. (2005). Quinolones Resistance and R-plasmids of 
some Gram-negative enteric Bacilli. Afr. J. Clin. Exp. Micro 6:14-20. 
http://www.ajol.info/viewarticle.php?id=17940  
David-West, K.B. (1983). Problems and prospects of livestock development in Nigeria. 
Journal of Animal Production 16:16 – 23. 
Davies, J. (1990). What are antibiotics? Archaic functions for modern activities. Mol. 
Microbial 4:1227 – 1232. 
Davies, J. (1994). Inactivation of antibiotics and the dissemination of resistance genes. 
Science 264: 375–381. 
Davis M.A., Hancock D.D., Besser T.E., Rice D.H., Gay J.M., Gay C., Gearhart  D.H., Gay, 
J.M., Gay, C., Gearhart, L. and Di Giacomo, R. (1999). Changes in antimicrobial 
resistance among Salmonella enterica serovar isolated from human and cattle in the 
Northwestern United States, 1982-1997. Emerg Infec Dis 5:802-806. 
Dayan, A. D. (1993). Allergy to antimicrobial residues in food: assessment of the risk to man. 
Vet. Microbiol. 35, 213-226. 
De Wasch, K., Okerman, L., Croubels, S. De Brabander, J., Van Hoofa J. and De Backer P. 
(1998). Detection of residues of tetracycline antibiotics in pork and chicken meat: 
correlation between results of screening and confirmatory tests. Analyst, 123: 2737–
2741. 
De Wasch, K., Okerman, L., Croubles, S., De Brabander, H., van Hoof, J. and De Backer, P. 
(1998). Detection of residues of tetracycline antibiotics in pork and chicken meat: 
correlation between results of screening and confirmatory tests. Analyst 123, 2737-
2741. 
Delgado, C., Rosegrant, M., Steinfeld, H., Ehui, S. & Courbois, C. (1999). Livestock to 2020. 
The Next Food Revolution. Food, Agriculture, and the Environment. Discussion 
Paper 28. International Food Policy Research Institute, Food and Agriculture 
Organization of the United Nations and the International Livestock Research Institute. 
IFPRI, Washington, D.C.  
Delgado, C.L., (2003). Rising consumption of meat and milk in developing countries has 
created a new food revolution. J. Nutr., 133: 3907S-3910S. 
Delwiche, M., Cox, E., Goddeeris, B., van Dorpe, C., de Baerdemaeker, J., Decuypere, E. 
and Sansen, W. (2000). A biosensor to detect penicillin residues in food. 
Transactions American Society of Agricultural Engineers, 43: 153–159. 
Dewdney, J. M., Maes, L., Raynaud, J. P., Blanc, F., Scheid, J. P., Jackson, T., Lens, S. and 
Verschueren, C. (1991). Risk assessment of antibiotic residues of β-lactams and 
macrolides in food products with regard to their immuno-allergic potential. Food 
Chem. Toxic. 29, 477-483. 
Diekema D.  J., Pfaller, M. A., and Turnidge J., (2000) Genetic relatedness of multidrug-
resistant, methicillin (oxacillin)-resistant Staphylococcus aureus bloodstream isolates 
from SENTRY Antimicrobial Resistance Surveillance Centers worldwide, 1998. 
SENTRY Participants Group. Microb Drug Resist  6:213–21. 
Dina, O.A. and Arowolo R.O.A. (1991). Some Considerations on veterinary drug use and 
supply in Nigeria. Re. d'Elevage Med. Vet. Pays Tropicaux, 44: 29-31. 
Dipeolu, M. A. (2002). Residues of Tetracycline Antibiotic in marketed goats and pigs in 
Lagos and Ogun States Nigeria.  Tropical Journal of Animal Science. 5 (2):  47-51. 
Dipeolu, M.A. Alonge, D.O. (2002).  Residues of streptomycin in meat sold for human 
consumption in some states of south western Nigeria. Archivos de Zootechnia. 51: 
477-480. 
Dipeolu, M.A. Ayinde, D.O. (2001). Tetracycline residue in commercial eggs and turkey 
meat sold for human consumption. Nig Poult. Sc. J. 1 (1): 12-16.  
Dipeolu, M.A., Eruvbetine D., Oguntona E.B., Bankole O.O. and Sowunmi K.S. (2005). 
Comparison of effects of antibiotics and enzyme inclusion in diets of laying birds. 
Arch. Zootec. 54: 3-11. 
Doern, G.V., Brueggemann, A., Holley, H.P.J. and Rauch, A.M. (1996). Antimicrobial 
Resistance of Streptococcus Pneumorice Recovered from Out-patients in United 
States during the Winter Months of 1994 – 1995: Results of a 30-Centre National 
Surveillance Study. Antimicrob. Agents Chemother. 40: 1208 – 1213. 
Domagk, G. J. (1935). Ein Beitrag zur Chemotherapie der bakteriellen infektionen. Dtsch. 
med. Wochenschr. 61: 250-253 
Dowdeney, J.M.,L. Meas, J.P Raynaud, F. Blance, J.P. Sheild T. Jackson, S. Verschueren, C. 
(1991). Risk assessment of antibiotics residues of beta-lactams and macrolides in food 
products with regard to their immune-allergic potential. Food Chem Toxicol 29:477-
483 
Doyle, M. E. (2006). Veterinary drug residues in processed meats: Potential health risk. Food 
Research Institute, Univ. of Wisconsin-Madison Briefings. 11p Food Research 
Institute, www.wisc.edu/fri/ accessed (March 10, 2009) 
Draisci, R., delli Quadri, F., Achene, L., Volpe, G., Palleschi, L. andPalleschi, G. (2001). A 
new electrochemical enzyme-linked immunosorbent assay for the screening of 
macrolide antibiotic residues in bovine meat. Analyst 126:1942-1946. 
Drlica, K. (2001). A strategy for fighting antibiotic resistance. ASM News, 67: 27-33. 
Duffy, G., O. M. Cloak, M. G. O‟Sullivan, A. Guillet, J. J. Sheridan, I. S. Blair, and D. A. 
McDowell. (1999). The incidence and antibiotic resistance profiles of Salmonella spp. 
on Irish retail meat products. Food Microbiol. 16:623–631. 
Dunlop, R. H., McEwen, S. A., Meek, A. H., Clarke, R. C., Black, W. D. and Friendship, 
R.M. (1998). Associations among antimicrobial drug treatments and antimicrobial 
resistance of fecal Escherichia coli of swine on 34 farrow-to-finish farms in Ontario, 
Canada. Preventive Veterinary Medicine 34 (4):283-305  
Earth Day 2008. Meat Cosumption.http://bentlyr.wordpress.com/2008/04/24/earth-day-
meat-consumption/ accessed 12/02/2009.  
Edder P., Corvi, C. (2001). Using of Charm II screening of antibiotic residues in food of 
animal origin, Mitt. Lebensm. Hyg. 92: 218-228 
EEC (1990). European Economic Community. Council Regulation 2377/90 of 26 June 1990 
laying down a Community procedure for the establishment of maximum residue 
limits of veterinary medicinal products in foodstuffs of animal origin. Off. J. Eur. 
Communities. L 224, pp. 1-8. 
EEC (1996). European Commission Council Directive 96/23/EC of 29 April 1996 on 
measures to monitor certain substances and residues thereof in live animals and 
animal products and repealing Directives 85/358/EEC and 86/469/EEC and Decision 
89/187/EEC and 91/664/EEC. Off. J. Eur. Union, L125 (23 May 1996) 10. 
EEC (2001). European Community notice to applicants and note for guidance. Establishment 
of maximum residue limits (MRLs) for residues of veterinary medicinal products in 
foodstuffs of animal origin. Off. J. Eur. Communities Volume 8. 
EEC, (1996). European Commission, Council Regulation 2377/90/EC of 26 June 1990 laying 
down a Community procedure for the establishment of maximum residue limits of 
veterinary medicinal products in foodstuffs of animal origin, Off. J. Eur. Union, L224 
(18 August 1990). 
Ehrlich, P. and Hata, S. (1910). Die Experimentelle Chemotherapie Der Spirillosen. Berlin. 
Damagk, G. 1935. Ein Beitrag Zur Chemotherapie Der Bakteriellen infektionen Dt. 
PhD Wocherschrift 61: 250 – 253. 
EMEA (2004). (MRL) summary reports on the scientific evaluations carried out by the 
Committee for Veterinary Medicinal Products (CVMP). EMEA 
http://www.emea.eu.int/index/indexv1.htm  (6.5.2006). 
Engel, H. W. B., van Leusden, F. M. and Nouws, J. F. M. (1983). Evaluation of the European 
Communities (EC) four-plate method for the detection of residues of antimicrobial 
drugs in slaughtered animals. Antimicrobials and Agriculture. Proceedings of 4th 
International Symposium on antibiotics in agriculture: benefits and malefits. 
Butterworths, London, UK, pp 491-499. 
European Community-EC (2001). Notice to applicants and note for guidance. Establishment 
of maximum residue limits (MRLs) for residues of veterinary medicinal products in 
foodstuffs of animal origin. Volume 8. 
Ezenduka E.V., Oboegbulem S.I., Nwanta J.A. and Onunkwo J.I. (2011). Prevalence of 
antimicrobial residues in raw table eggs from farms and retail outlets in Enugu State, 
Nigeria. Trop Anim Health Prod. 43 (3): 557-559 
Fagbamila I., Kabir J., Abdu P., Omeiza, G., Ankeli, P., Ngulukun, S., Muhammad, M. and 
Umoh, J. (2010). Antimicrobial Screening of Commercial Eggs and Determination of 
Tetracycline Residue Using Two Microbiological Methods. International Journal of 
Poultry Science 9 (10): 959-962 
Fairbrother J.M. and Nadeau, E. (2006). Escherichia coli: on-farm contamination of animals 
Rev Sci Tech Off Int Epiz  25:555-569. 
FAO (1996). World Food Summit. Rome, Italy 13-17 September, 1996 
http://www.fao.org/wfs/index_en.htm  
FAO (1999). Manual on livestock diseases surveillance and information systems FAO 
Animal health Manual, 8, Rome 71Pp 
FAO (2002a). Livestock: intensification and its risks, pp. 58-63 In: World Agriculture: 
Towards 2015/2030. Summary report, Rome, Pp. 99. 
FAO (2002b). Prospects for food and nutrition. p14-20. In: World Agriculture: Towards 
2015/2030. Summary report, Rome, p. 99. 
FAO (2009). The State Of Food and Agriculture.  Food and Agriculture Organization of the 
United Nations, Rome pp 180. ISBN 978-92-5-106215-9. 
FAO (2000). Global Perspectives: Agriculture: Towards 2015/30. Technical Interim Report. 
Food and Agriculture Organization of the United Nations, Rome, Italy. FAO's 
Economic and Social Department.  
FAO (2001). Undernourishment and Economic Growth. FAO Economic and Social 
Development Paper No.147. Food and Agriculture Organization of the United 
Nations, Rome, Italy. 
Food and Agricultural Organisation (2010). A system of integrated agricultural censuses and 
surveys; World Programme for the Census of Agriculture Vol. 1: 174p ISBN 92-5-
105375-8 
FAO/WHO, (2005). National Food Safety Systems in Africa; A Situation Analysis Regional 
Conference on Food Safety for Africa Harare, Zimbabwe 3-6 October 2005 Pp14. 
FAO/WHO/OIE (2008) Expert Meeting on Critically Important Antimicrobials Report of the 
FAO/WHO/OIE Expert Meeting FAO Headquarters, Rome 26-30 November 2007. 
67p. ISBN 978-92-5-106009-4 
FAOSTAT (2009). Food and Agriculture Organization of the United Nations Statistical 
Databases, Statistics Division, Rome, Italy.  
FAOSTAT (2000). FAO Statistical Databases (CD-ROM), Food and Agriculture 
Organization of the United Nations, Rome, Italy 
FDA/FSIS (2009).The Food Safety Working Group: Food and Drug Administration (FDA) 
of the U.S. Department of Health and Human Services and the Food Safety and 
Inspection Service FSIS of the U.S. Department of Agriculture (USDA) 
http://www.foodsafetyworkinggroup.gov  
Fein, S. B., Lin, J. and Levy, A. S. (1995). Foodborne illness: perception, experience, and 
preventive behavior in the United States. J Food Prot 58:1405-1411. 
Federal Government of Nigeria (FGN) (1988). The Animal Disease Control Decree No. 10 of 
1988 
Federal Government of Nigeria - FGN (1993). National Food and Drugs Administration and 
Control (NAFDAC) Decree No. 15 of 1993 
Fingleton (2009). Legislation for veterinary drugs control. http://www.fao.org/legal/pub-
e.htm 
Fitzpatrick, S., Brynes, S. and Guest, G. (1995). Dietary intake estimates as a means to the 
harmonization of maximum residue levels for veterinary drugs 1. Concept. J. Vet. 
Pharmacol. Therap. 18: 325-327. 
Fleming, A. (1929). On the antibacterial action of cultures of a Penicillium, with special 
reference to their use in the isolation of B. influenzae. British Journal of Experimental 
Pathology. 10: 226-236. 
Fletouris, D.J., Psomas, J.E. and Botsoglou, N.A. (1990). Trace Analysis of Oxytetracycline 
and Tetracycline in Milk by High-Performance Liquid Chromatography." Journal of 
Agricultural and Food Chemistry 38: 1913-17.  
Friedmann, H. (1998). The political economy of food: the rise and fall of the postwar 
international food order. American Journal of Sociology 104: 597-641. 
FSIS (2006). National Residue Monitoring Plan 
http://www.fsis.usda.gov/PDF/2006_Blue_Book_Appendices.pdf     
Gaudin, V., Maris, P., Fuselier, R., Ribouchon, J.L., Cadieu, N. and Rault, A. (2004). 
Validation of a microbiological method: The STAR protocol, a five-plate test, for the 
screening of antibiotic residues in milk. Food Additives and Contaminants 21:422–
433. 
Glazko A.J., Dill, W.A., Kinkel A.W. (1977). Absorption and excretion of parenteral doses of 
chloramphenicol sodium succinate in comparison with per oral doses of 
chloramphenicol. Clin Pharmacol Ther 21: 104-116.                
Gomes, E.R. and Demoly, P. (2005). Epidemiology of hypersensitivity drug reaction. Curr 
Opin Allerg Clin Immunol 5:309-316.  
Gomna, A. and Rana, K. (2007). Inter-household and intra-household patterns of fish and 
meat consumption in fishing communities in two states in Nigeria. Bri Journ Nutr 
97(1): 145-152  
Gorbach, S. L. (1993). Perturbation of intestinal microflora. Vet Human Toxicol 35:15-23. 
Greenless, K. J. (2003). Animal drug human food safety toxicology and antimicrobial 
resistance-the square peg. Int. J. Toxicol. 22:131-134. 
Greenwood, D. (1995). History Introduction. In D. Greenwood, Ed. Antimicrobial 
Chemotherapy, New York Oxford University Press, Ho. pp122 
Greenwood, D. (1997). Mode of Action of Antibiotic and Chemotherapy. In F.O‟Grady, H.P. 
Lambert, R.G. finch and D. Greenwood, Eds. Antibiotic and Chemotherapy. New 
York Churchill-Livingstone. 
Greenwood, D. (2009). History Introduction, p. 3-10. In Antibiotic and chemotherapy: anti-
infective agents and their use in therapy. Finch, R. G., Greenwood, D., Norrrby, S. 
th
R., and Whitley, R.  J. Ed. (8  Ed.) New York Churchill-Livingstone. 964p, 
rd
Greenwood, D. and O'Grady, F. 3  eds, (1997). The scientific basis of antimicrobial 
chemotherapy. Cambridge University Press, Cambridge, 341p. 
Greenwood, D. and Whitney, R. J. (2009). Modes of Action, p. 11-24. In Antibiotic and 
chemotherapy: anti-infective agents and their use in therapy. Finch, R. G., 
th
Greenwood, D., Norrrby, S. R., and Whitley, R.  J. Ed. (8  Ed.) New York 
Churchill-Livingstone. 964p. 
Griggs D.J., Gensberg K., Piddock L.J.V. (1996) Mutations in gyrA gene of quinolone-
resistant Salmonella serotypes isolated from humans and animals. Antimicrob 
Agents Chemother 1996;40:1009–13. 
Guest, G.B. and Paige, J.C. (1991). The magnitude of the tissue residue problem with regard 
to consumer needs. J. Am.Vet. Med. Assoc. 198:805-808. 
Gustafon, R.H. and Bowen, R.E. (1997). Antibiotic use in animal agriculture. J. Appl. 
Microbiol.,83,531-541. 
Gyles, C.L. (2007). Shiga toxin-producing Escherichia coli: An overview. J Anim Sci 
85:E45–E62  
Hald, B., Skovgaard, H., Bang, D.D., Pedersen, K., Dybdahl, J., Jespersen, J.B. and Madsen, 
M. (2004). Flies and Campylobacter infection of broiler flocks. Emerg Infec Dis 
10:1490-1492. 
Hart, C.A. and Kariuki, S. (1998). Antimicrobial resistance in developing countries Brit Med 
Journ 317: 647-650   
Hedges, R.W., and Jacob, A.E. (1971). Transportation of Ampicillin Resistance from RP4 to 
other Replicons. Mol. Genet. 132:31-40. 
Heeschen, W.H. and Bluthgen, A. (1991). Veterinary drugs and pharmacologically active 
compounds. Monograph on Residues and Contaminants in Milk and Milk Products. 
IDF, Brussel: 13–69. 
Heitzman R.J., ed. (1994). Veterinary drug residues – Residues in food-producing animals 
and their products: Reference materials and methods. Oxford: Blackwell Scientific 
Publications. pp 318. 
Helms, M., Vastrup, P., Gerner-Smidt, P. and Molbak, K. (2002). Excess mortality associated 
with antimicrobial drug resisitant S. typhimurium. Emerg. infect. Dis. 8(15), 490-495. 
Higgins, H. C., McEvoy, J. D. G., Lynas, L. and Fagan, N. P. (1999). Evaluation of a single 
plate microbiological growth inhibition assay as a screening test for the presence of 
antimicrobial agents in compound animal feedingstuffs at therapeutic and 
contaminating concentrations. Food Addit. Contam. 16, 543-554. 
Hinton, M., Linton, A.H., Hedges, A.J., (1985). The ecology of Escherichia coli in calves 
reared as dairy-cow replacements. J Appl Bacteriol 58:131-138. 
Holmberg, SD, SI Soloman and PA Blake. (1987). Health and economic importance of 
antimicrobial agents. Rev. Inf. Dis. 9:1065-78. 
Ibrahim A. and Moats W. A. (1994). Effect of Cooking Procedures on Oxytetracycline 
Residues in Lamb Muscle J. Agric. Food Chem., Vol. 42, No. 11, 2561-2563 
Ibrahim, A., Junaidu A. and Garba M (2010). Multiple antibiotic residues in meat from 
slaughtered cattle in Nigeria. The Internet Journal of Veterinary Medicine; 8(1). 
IPCS (1987). International Programme on Chemical Safety in cooperation with the Joint 
FAO/WHO Expert Committee on Food Additives (JECFA). Environmental Health 
Criteria 70, Principles for the safety assessment of food additives and contaminants 
in food. World Health Organization, Geneva, Switzerland. 
Isoherranen, N. and Soback, S. (1999). Chromatographic methods for analysis of 
aminoglycoside antibiotics. J. AOAC. Int 82:1017-1045. 
Jackson, G. S. (1980). Safety assessment of drug residues. J Am Vet Med Assoc 176, 1141-
1144. 
Jacoby, G. A. and G. L. Archer (1991). New Mechanism of Bacterial Resistance to 
Antimicrobial Agents. New Engl J Mid 324:601 – 612. 
Jafari, M.T., Khayamian, V. Shaer, V. and Zarei, N. (2007). Determination of veterinary 
drugs residues in chicken meat using corona discharge ion mobility spectrometry. 
Analytica Chima Acta 851:147-153. 
Jawetz, E., Melnick, J. and E. A. Adelberg. (1984). Review of medical microbiology, 16th 
Edn. Long Medical Publication, Los Altos, California. pp. 122-144. 
JECFA Joint Expert Committee on Food Additives (2003). Evaluation of certain veterinary 
drug residues in food. WHO Technical Report Series 918:5-11. 
Jones R. N. and Pfaller, M. A. (1998). Bacterial resistance: a worldwide problem. Diagn 
Microbiol Infect Dis 31:379–88. 
Kabir, J. Umoh, J. U. and Umoh, V.J. (1999). Characterization and screening for 
antimicrobial substances of slaughtered cattle in Zaria, Nigeria. Health and Hygiene 
20: 20-23.   
Kabir, J., Umoh, V.J., Audu-okoh, E., Umoh, J.U. and Kwaga, J.K.P. (2004). Veterinary drug 
used in poultry farms and determination of antimicrobial drug residues in 
commercial eggs and slaughtered chicken in Kaduna State, Nigeria. Food Control 
15:99-105.  
Kaneene  J.B. and R. Miller (1997). Problems Associated with drug residues in beef from 
feeds and therapy. Rev Sci Tech Off Int Epiz 16:694-708.  
Kanny, G. Puygrenier, J., Beaudoin, E. and Moneret-Vautrin, D.A. (1994). Food anaphylactic 
shock: implication of penicillin residues. Allerg Immunol 26:181-183. 
Karimuribo, E.D., Mdegela, R.H., Kusiluka, L.J.M. and Kambarage, D.M. (2005). 
Assessment of Antimicrobial Usage and Antimicrobial Residues in Milk on Small 
Holder Farms in Morogoro, Tanzania. Bull Anim Health  Prod  Afr. 53:234-241. 
Kathleen, K., Lee, M.D. and Maurer, J.J. (2003). Antibiotics: Mode of Netron Mechanisms of 
Resistance and Transfer. Microbiol Food Safety  Ani Agric 6:45-55. 
Katz, S.E. (1982). Microbiological Assay Procedures for Antibiotic Residues. In: 
Agricultural Uses of Antibiotics. American Chemical Society Press, NJ; pp142–153 
Kennedy D.G., Mc Cracken R..J., Cannavan A. and Hewith S.A. (1998). Use of liquid 
chromatography-mass spectrometry in the analysis of residues of antibiotics in meat 
and milk. J. Chromatogr. 812, 77-98. 
Kennedy, D. G., Cannavan, A. and McCracken, R. J. (2000). Regulatory problems caused by 
contamination, a frequently overlooked cause of veterinary drug residues. J 
Chromatogr 882:37-52. 
Khan A., Das S.C., Ramamurthy T. and Sikandar A. (2002). Antibiotic Resistance, Virulence 
Gene, and Molecular Profiles of Shiga Toxin-Producing Escherichia coli Isolates 
from Diverse Sourecs in Calcutta, India. J Clin Microbiol. 40 (6): 2009-2015 
Kijima-Tanaka, M., Ishihara, K., Morioka, A., Kojima, A., Ohzono, T. and Ogikubo, K, 
(2003). A national surveillance of antimicrobial resistance in Escherichia coli isolated 
from food-producing animals in Japan. J Antimicrob Chemother 51:447– 51. 
Koch, R. (1876). Untersuchungen ueber Bakterien V. Die Aetiologie der Milzbrand-
Krankheit, begruendent auf die Entwicklungsgeschichte des Bacillus Anthracis. Beitr. 
z. Biol. D. Pflanzen 2: 277-310. (In Milestones in Microbiology: 1556 to 1940, 
translated and edited by Thomas D. Brock, ASM Press. 1998, pp89. 
Korsrud, G.O. and MacNeil. J.D. (1987). A Comparison of Three Bioassay Techniques and 
High Performance Liquid Chromatography for the Detection of Chlortetracycline 
Rsidues in Swine Tissues. Food Additives and Contaminants 5:149-53.  
Kruse, H., Lovseth, A., Olsvik, O., and Sundsfjord, A. (1998). Transmission of Van A-type 
vancomycin resistant enterococci and Van A resistance elements between chicken and 
humans at avoparcin-exposed farms. Microb Drug Resist Winter; 4:313-318 
Kuhne, M. Ihnen, D., Moller, G. and Agthe, O. (2000). Stability of tetracycline in water and 
manure. J. Vet. Med. 47:379-384.   
Kuhne, M., Wegmann, S., Kobe, V. and Fries, R. (2000). Tetracycline residues in bones of 
slaughtered animals. Food Control 11:175–180. 
KuKanich, B., Gehring, R., Webb, A. I., Craigmill, A. L. and Riviere, J. E. (2005). Effect of 
formulation and route of administration on tissue residues and withdrawal times. J 
Am Vet Med Assoc 227:1574- 1577. 
Kumai, Y.,  Suzuki, Y., Tanaka, Y., Shima, K., Bhadra, R.K., Yamasaki, S. Kuroda, K. and 
Endo, G. (2005). Characterization of multidrug-resistance phenotypes and genotypes 
of Escherichia coli strains isolated from swine from an abattoir in Osaka, Japan. 
Epidemiol. Infect. 133:59-70. 
Lambie N, Ngeleka M, Brown G, Ryan J. (2000) Retrospective study on Escherichia coli 
infection in broilers subjected to postmortem examination and antibiotic resistance of 
isolates in Trinidad. Avian Dis 44:155-60. 
Lancini, G. F., Parenti, G., and Gallo, G. (1995). The mechanism of action of antibiotics, p. 
37–83. In Antibiotics: a multidisciplinary approach. Plenum Press, New York, N.Y. 
Landicho, E. F. (1996). Veterinary drug residues in food. College of Veterinary Medicine, 
University of the Philippines, Los Banos, pp.1-30. 
Lathers, C. M. (2001). Role of veterinary medicine in public health: antibiotic use in food 
animals and humans and the effect on evolution of antibacterial resistance. J. Clin. 
Pharmacol. 41:595-599. 
Lee, M.H., Lee, H.J. and Ryu, P.D. (2001). Public health risks: chemical and antibiotic 
residues. Asian-Aust J Anim Sci 14:402- 413.  
Levy, S. B. (1992). The antibiotic paradox: how miracle drugs are destroying the miracle. 
Plenum Press, New York, N.Y. pp79 
Levy, S. B. (1997). Antibiotic Resistance: An Ecological Perspective. In Chadwick D.J. and 
Goode, J. Eds. Antibiotic Resistance: Origins, Evolution and Spread. New York 
Wiley: 1-14.  
Levy, S. B. (1998). Multidrug resistance – a sign of the times. N Engl J Med 338:1376-1378.  
Levy, S.B., FitzGerald, G.B. and Macone, A.B. (1976). Spread of antibiotic resistant 
plasmids from chicken to chicken and from chicken to man. Nature 260:40–42. 
Linton, A.H., Hinton, M.H. and Al Chalaby, Z.A. (1985). Monitoring for antibiotic resistance 
in enterococci consequent upon feeding growth promoters active against gram-
positive bacteria. J Vet Pharmacol Ther 8: 62-70 
Linton, A.H., Hedges, A.J. and Bennet, P.M. (1988). Monitoring for the development of 
antimicrobial resistance during the use of olaquindox as a feed additive on 
commercial pig farms. J. Appl. Bacteriol. 64: 311-27 
Livermore, D.M. (1995). β-lactamases in laboratory and clinical resistance. Clinical 
Microbiological Reviews, 8, 557–584. 
Luga, I.I., Akodu, I., Mhomga, I., Allam, L., Ajogi, I., Umoh, V.J. and Kwaga, J.K.P. (2007). 
Antimicrobial resistance of shigatoxin producing Escherichia coli, O157: H7 O157 
NM isolates from water fed to cattle in northwestern, Nigeria. Asian J. Anim. Vet. 
Ad. 2: 205-211.  
Lynas, L., Currie, D., McCaughey, W.J., McEvoy, J.D.G. and Kennedy, D.G. (1998). 
Contamination of animal feedingstuffs with undeclared antimicrobial additives. 
Food Addit Contam 15:162-170. 
MacNeil, J. D., Martz, V. K., Korsrud, G.O., Salisbury, C.D.C., Oka, H., Epstein, R.L. and 
Barnes, C.J. (1996). Chlortetracycline, Oxytetracycline and Tetracycline in Edible 
Animal Tissues. (1996). AOAC Official Methods of Analysis, J. AOAC Int. 79: 405 - 
417. AOAC International (16th ed). 
MAF (2003). Recommendations for the use of antimicrobial agents in the treatment of the 
most significant infectious diseases in animals. TheMinistry of Agriculture and 
Forestry. Memorandum 2003:9a. Helsinki, Finland. 
Magner, L.N. (1992). A history of medicine.  M. Dekker Pub, Pp 393. 
Maina, J.A. (1986). Animal health in subhumid Nigeria. In Livestock System Research in 
Nigeria's Sub-Humid Zone; Von Kaufmann, R, Charter, S. and Blench, R.(ed.) Pp 
167-188. Ethiopia, Addis Ababa, ILCA. 
Marshall, B., Petrowski, D. and Levy, S.B. (1990). – Inter- and intra-species spread of 
Escherichia coli in a farm environment in the absence of antibiotic usage. Proc. natl 
Acad. Sci. USA, 87:6609-6613. 
Martel, A., Baele, M., Devriese, L.A., Goossens, H., Wisselink, H.J., Decostere, A. and 
Haesebrouck, F. (2001). Prevalence and mechanism of resistance against macrolides 
and lincosamides in Streptococcus suis isolates. Vet Microbiol 83:287-297. 
Martin, L.J., Fyfe, M., Dore, K., Buxton, J.A., Pollari, F., Henry, B., Middleton, D., Ahmed, 
R., Jamieson, F., Ciebin, B., McEwen S.A. and Wilson J.B. (2004). Multi-Provincial 
Salmonella Typhimurium Case-Control Study Steering Committee: Increased burden 
of illness associated with antimicrobial-resistant Salmonella enterica serotype 
typhimurium infections. J. Infect. Dis. 189: 377–384. 
Mazel, D. and Davies, J. (1998). Antibiotic Resistance. The Big Picture. Adv Exp Med Biol. 
456: 1-6. 
McCaughey, W.J., Eillot, C. T., Campbell, J. N. Blanchflower, W.J. and Rice, D.A. (1990). 
Tissue residues in pigs fed on meal contaminated with sulphadimidine during 
mixing. Ir. Vet. J. 48:127-130 
McConville, M., Dijkstra, J., Stamm, J., van Seane, J. and Nouws, J. (1995). Effects of 
sarafloxacin hydrochloride on human enteric bacteria under simulated human gut 
conditions. Vet Quart 17:1-5. 
McCracken, R.J., Spence D.E. and Kennedy, D.G. (2000). Comparison of extraction 
techniques for the recovery of veterinary drug residues from animal tissues. Food 
Additives and Contaminants 17:907-914. 
McEvoy, J. D. G. (2002). Contamination of animal feedingstuffs as a cause of residues in 
food: a review of regulatory aspects, incidence and control. Anal Chim Acta 473:3-
26. 
Mead, P., Slutsker, L., Dietz, V., McCaign, L., Bresee, J. and Shapiro, C. (1999). Food-
related illness and death in the United States. Emerg Infect Dis 5:607-25. 
Mellon, M., Benbrook, C. and Benbrook, K.L.  (2001). Hogging It! Estimates of 
Antimicrobial Abuse in Livestock. Union of Concerned Scientists: Cambridge, MA, 
January, 2001. http://www.ucsusa.org/publications  (accessed 05/06/2007) 
Meng, J. and Doyle, M.P. (1997). Emerging issues in microbiological food safety. Annu Rev 
Nutr 17: 255–75. 
Millodot, M. (2009). Dictionary of Optometry and Visual Science, 7th edition. Butterworth-
Heinemann p450. 
Miranda, J.M, Vazquez, B. I. Fente, C. A. Barros-Velazquez, J. Cepeda, A. and. Franco, C. 
M. (2008). Evolution of Resistance in Poultry Intestinal Escherichia coli During 
Three Commonly Used Antimicrobial Therapeutic Treatments in Poultry. Poult. Sci. 
87, 1643-1648.  
Mitchell, J.M., Griffiths, M.W., McEven, S.A., McNab, W.B. and Yee, J. (1998). 
Antimicrobial drug residues in milk and meat: causes, concerns, prevalence, 
regulations, tests, and test performance. J. Food Prot. 61, 742-756.  
Mitema, E.S., Kikuvi, G.M., Wegener, H.C. and Stohr, K. (2001). An assessment of 
antimicrobial consumption in food producing animals in Kenya. Journal of Veterinary 
Pharmacology & Therapeutics 24 (6):385-390. 
Moats, W.A. (1986). Determination of tetracycline antibiotics in tissue and blood serum of 
cattle and swine by high performance liquid chromatography. J Chromatogr 358:253-
259. 
Moore, K.A. and Osterholm M. T. (1999). Quinolone-Resistant Campylobacter jejuni 
Infections in Minnesota, 1992-1998. The New England Journal of Medicine 340 
(20):1525. 
Moulin, G.  Lambert, C. (2008). International approach for veterinary medicinal products: 
OIE and Codex alimentarius OIE Conference on veterinary medicinal products in 
Africa, Dakar, 25-27 March 2008. 1- 8. 
Muriuki, F.K., Ogara, W.O., Njeruh, F.M. and Mitema E.S. (2001). Tetracycline residue 
levels in cattle meat from Nairobi slaughterhouse in Kenya. Journal of vet sciences 2 
(2): 97-101  
NAFDAC, National Agency for Food and Drug Administration and Control (1996). Ban on 
the use of nitrofuran in livestock and poultry feeds. National Agency for Food and 
Drug Administration and Control, Alert No. 10, Lagos. 
Nataro, J. P., and Kaper, J.B. (1998). Diarrheagenic Escherichia coli. Clin Microbiol Rev. 
11:142–201. 
National Bureau of Statistics (2006). Fed. Republic of Nigeria 2006 Population Census 
http://www.nigerianstat.gov.ng th (accessed on 24  February, 2008). 
National Research Council (1998). Issues specific to antibiotics. In: National Research 
Council Institute of Medicine. The Use of Drugs in Food Animals: Benefits and Risks. 
Washington, D.C. National Academy Press: 255p. 
NCCLS- National Committee for Clinical Laboratory Standards (1999). Performance 
Standard of Antibiomicrobial Desk and Dilution Susceptibility Tests for Bacteria 
Isolated from Animals. Approved Standards M31-A. 
Neu, H.C. (1992). The crisis in Antibiotic Resistance. Science 257:1064-1073. 
Nhiem, D.V., Paulsen, P., Suriyasathaporn, W., Smulders, F.J.M., Kyule, M.N., Baumann, 
M.P.O., Zessin, K.H. and Ngano, P.H. (2006). Preliminary Analysis of Tetracycline 
Residues in Marketed Pork in Hanoi, Vietnam. Ann. N.Y. Acad. Sci. 1081: 534–542. 
Nield, B.S., Holmes, A.J., Gillings, M.R., Recchia, G.D., Mabbutt, B.C., Nevalonen, K.M. 
and Stokes, H.W. (2001). Recovering of New Integron Classes from Environmental 
DNA. FEMS Microbiol Let 195:59-65. 
Nijsten, R., London, N., van den Bogaard, A. and Stobberingh, E. (1994). – Resistance in 
faecal Escherichia coli isolated from pig farmers and abattoir workers. Epidemiol. 
Infect., 113:45-52. 
Nisha, A.R. (2008). Antibiotic Residues - A Global Health Hazard. Veterinary World 1:375-
377 
Nonga, H.E., Mariki, E.D., Karimuuribo, E. and Mdegela, R.H. (2009). Assessment of 
Antimicrobial Usage and Antimicrobial Residues in Broiler Chickens in Morogoro 
Municipality, Tanzania. Pakistan Journal of Nutrition 8:203-207. 
Nord, C. E. and Edlund, C. (1990). Impact of antimicrobial agents on human intestinal 
microflora. J Chemother 2:218-237. 
Nouws, J.F.M. (1984). Irritation, bioavailability, and residue aspects of ten oxytetracycline 
formulations administered intramuscularly to pigs. Vet Quart 6:80-84. 
Nouws, J.F.M.(1990). Injection sites and withdrawal times. Ann Rech Vet 21:145S-150S. 
Oboegbulem, S.I. and Fidelis, A.P. (1996). Detection of Microbial Residues in Poultry meat 
and slaughter cattle in Nigeria: Meat science. 43:71-74. 
Ogundipe, G.A.T (1993). Economic importance of drug abuse in animals. In: Drug abuse in 
man from animal perspective: health, socioeconomic and legal implications. 
nd
proceeding of the 2  annual workshop of the Association of Private Veterinary 
Medical Practitioners, Oyo/Osun States Branch, Ibadan pp 88-98. 
Ojo, O.E., Oyekunle, M.A., Ogunleye, A.O., Otesile, E.B. (2009). E. coli O157:H7 in food 
animals in part of S/Western Nigeria: Prevalence and invitro antimicrobial 
susceptibility. Trop.Vet. 26: 23-30. 
Oka, H., Ito, Y, Ikai, Y, Matsumoto, H., Kato, K., Yamamoto, I., Shimizu, M., Kawamura N., 
Miyazaki Y., Nojiri, T., Okumura, N., Ohmi, S., Sato T and Mori, G. (2001). Survey 
of Residual Tetracyclines in Kidneys of Diseased Animals in Aichi Prefecture, Japan 
(1985–1997).   Journal of AOAC International, 84 (2) 350-353. 
Oka, H., Ito, Y. and Matsumoto, H. (2000). Chromatographic analysis of tetracycline 
antibiotics in foods. Journal of Chromatography A 882(1-2):109-133. 
Okeke, I.N.,   Laxminarayan, R., Butta, Z.A., Duse A. G., Jenkins P., O‟Brien, T.F., Pabloso-
Mendez, A. and Klugman, K.P. (2005). Antimicrobial resistance in developing 
countries. Part i Recent Trends and current status. Lancet Ifectious Disease 5:481-493 
Okeke, I.N., Aboderin, O.A., Byarugaba, D.K., Ojo, K.K., Opintan, J.A. (2007). Growing 
problem of multidrug-resistant enteric pathogens in Africa. Emerg. Infect. Dis. 
th
http://www.cdc.gov/EID/content/13/11/1640.htm   (accessed  18 , August 2009). 
Okeke, I.N., Adebayo, L. And Edellman, R. (1999). Socioeconomics and Behavioural Factors 
Leading toAcquired Bacterial Resistance to Antibiotics in Developing Countries. 
Emerg Inf Dis 5:18-27. 
Okerman, L., de Wasch K. and van Hoof, J. (1998a). Detection of antibiotics in muscle tissue 
with microbiological inhibition tests: Effects of matrix. Analyst 123:2361–2365. 
Okerman, L., van Hoof, J. and Debeuckelaere, W. (1998b). Evaluation of the European four-
plate test as a tool for screening antibiotic residues in meat samples from retail outlets. 
Journal of AOAC International 81:51–56. 
Okolo, M.I. (1986). Bacterial drug resistance in meat animals: a review. Int J Zoonoses; 
13:143-152. 
Olatoye, I. O. (2010). The incidence and antibiotics susceptibility of Escherichia      coli 
O157:H7 from beef in Ibadan Municipal, Nigeria. Afr.  Jour Biotech, 9:1196-1199 
Orden, J., Ruiz Santa Quiteria, J., Garcia, S. De La Fuente, R. (1999). In vitro activities of E. 
coli strains isolated from diarrhoeic dairy calves. Antimicrob Ag Chemother 43:510-
513. 
Osho, G.S. and Asghar, N. (2004). Consumerism: Statistical Estimation of Nigeria Meat 
Demand. Proceedings of the Academy for Studies in International Business, New 
Orleanss 4:47-56.  
Owoade AA, Oluwayelu DO, Fagbohun OA, Ammerlaan W, Mulders MN, Muller CP 
(2004). Serologic evidence of chicken infectious anemia in commercial chicken 
flocks in Southwest Nigeria. Avian Dis. 48: 202-205. 
Oyekunle, M.A., and Olubi, A. (1992). An investigation of antibiotic residues in broiler 
chicken meat .Nig. J. Anim. Prod. 19:52-56 
Paige, J.C., Tollefson, L. and Miller, M. (1997). Public health impact on drug residues in 
animal tissues. Vet Human Toxicol 39:162-169. 
Panin, A.N., Violin B.V., Kovalev, V.F. (1997). Some problems due to antibiotic resistance 
and application of feed antibiotics in Russia. In: The Medical Impact of the Use of 
Antimicrobials in Food Animals: October 13, 1997-October 17, 1997; Berlin, 
Germany. Geneva: World Health Organization. 
Paulsen, I.T. (2003). Multidrug efflux pumps and resistance: regulation and evolution. Curr 
Opin Microbiol 6:446-51. 
Perrin-Guyomard, A., Cottin, S., Corpet, D.E., Boisseau, J. and Poul, J.M. (2001). Evaluation 
of residual and therapeutic doses of tetracycline in the human-flora-associated 
(HFA) mice model. Regul. Toxicol. Pharmacol. 34:125-136. 
Pfaller, M. A.,  Acar, J., Jones, R. N., Verhoef, J., Turnidge, J., and  Sader, H.S. (2001). 
Integration of Molecular Characterization of Microorganisms in a Global 
Antimicrobial Resistance Surveillance Program. Clin Infect Dis: 32:S156-S167 
Phillips, I., Casewell, M., Cox, T., De Groot, B., Friis, C., Jones, R., Nightingale, C., Preston, 
R., Waddell, J., (2004). Does the use of antibiotics in food animals pose a risk 
tohuman health? A critical review of published data. J  Antimicrob Chemother 23:28–
52. 
Ploy, M.C., Lambert, T., Gassama, A. and Denis, F. (2000). The role of integrons in 
dissemination of antibiotic resistance. Annales de Biologie Clinique, 58:439-444. 
Popelka, P.J., Nagy, J., GermusˇKa, R., Marcincak S.,  Jevinova, P. and De Rijk, A. (2005). 
Comparison of various assays used for detection of beta-lactam antibiotics in poultry 
meat. Food Additives and Contaminants 22: 557–562 
Posyniak, A. Zmudzki, J., Ellis, R.L., Semeniuk, S., and  Niedzielska, J. (1999). Methods of 
Tetracycline Residues in Analysis in Milk. J. AOAC Int. 82: 862-865. 
Posyniak, A., Mitrowska, K., Zmudzki, J., and Niedzielska, J. (2005). Analytical procedure 
for the determination of chlortetracycline and 4- epi-chlortetracycline in pig kidneys. 
Journal of Chromatography A, 1088, 169–174. 
Prescott, J. F. (2000a). Beta-lactam antibiotics: penicillins. In: Prescott, J. F., Baggot, J. D. 
and Walker, R. D. (eds.) Antimicrobial Therapy in Veterinary Medicine, 3rd ed. 
Ames, Iowa, USA, pp. 105-126. 
Prescott, J. F. (2000b). Tetracyclines. In: Prescott, J. F., Baggot, J. D. and Quart. 12, 129-138. 
Prescott, J. F. Antibiotics (1997). Miracle drugs or pig food? Can Vet J 12: 763-6 
Prescott, J.F. and Baggot, D.J. (1993). Antimicrobial therapy in veterinary medicine. 
International Book Distributing Co., India, pp.564-565. 
Rahman, D., Khan, M.K. and Malik, K. (2001). Antibiotic Resistance and Detection of β-
lactamase in Bacterial Strains of Staphylocci and Escherichia coli isolated from 
foodstuffs. World Journal of Microbiology and Biotechnology 17:863-868.  
Raison-Peyron, N., Messaad, D., Bousquet, J. and Demoly, P. (2001). Anaphylaxis to beef in 
penicillin-allergic patient. Allergy 56:796-797. 
Rangel, J.M., Sparling, P.H., Crowe, C. Griffin, P.M. and Swerdlow, D.L. (2005). 
Epidemiology of E. coli O157 outbreaks, United States, 1982-2002. Emerg. Infect. 
Dis., 11: 63-70. 
Ranheim, B., Ween, H., Egeli, A. K., Hormazabal, V., Yndestad, M. and Soli, N. E. (2002). 
Benzathine penicillin G and procaine penicillin G inpiglets: comparison of 
intramuscular and subcutaneous injection. Vet. Res. Commun. 26: 459-465 
Recchia, G. D., and R. M. Hall. (1995). Gene cassettes: a new class of mobile element. 
Microbiology 141:3015–3027. 
Reybroeck, W. (2000). Performance of the Premitest using naturally contaminated meat. 
Poster presented at EuroResidue IV, Veldhoven, The Netherlands. 8–10 May 2003. 
Riedl, M. A. and Casillas, A. M. (2003). Adverse drug reactions: types and treatment options. 
Am Fam Physician 68:1781-1790.  
Riley, L.W., Remis, R.S., Helgerson, S.D., Mc Gee, H.B., Wells, B.K., Davis, R., Hebert, J., 
Olcott, E.S., Johnson, L., Hargrett, N.T., Blake, P.A., Cohen, M.L. (1983). 
.Haemorrhagic colitis associated with a name E. coli serotype. N. Engl. Med. 24: 
681-685. 
Riviere, J.E. and Spoo, J.W. (1995). Chemical residues in tissues of food animals In: 
th
Veterinary pharmacology and therapeutics 5  Ed, (Edited by H.R. Adams) Iowa 
State Univ. press, pg: 1148-1150. 
Riviere, J.E. and Sundlof, S.F. (2001). Chemical Residue in Tissues of Food Animals. In: 
Veterinary Pharmacology and Therapeutics. Adams HR: 8th Edition; Blackwell 
Publishing Professional Iowa pp1166-1174. 
Roberts, M.C. (1996). Tetracycline resistance determinants: mechanisms of action, 
regulations of expression, genetic mobility and distribution. FEMSI Microbiology 
Reviews 19:1-24. 
Roderick, S, Stevenson, P., Mwendia, C, and  Okech, G. (2000). The Use of Trypanocides 
and Antibiotics by Maasai Pastoralists. Tropical Animal Health and Production 
32:361-374. 
Rodrıguez, I., Rodicio, M.R., Mendoza, M.C and Cruz- Martı´n., M. (2006). Large 
conjugative plasmids from clinical strains of Salmonella enterica serovar virchow 
contain a class 2 integron in addition to class 1 integrons and several nonintegron- 
associated drug resistance determinants. Antimicrobial Agents Chemotherapy. 
50:1603–1607. 
Rutter, J.M. (1997) Use of anti-infective drugs in the UK: types of use and 
conditions/legislation for applications. In The Medical Impact of the Use of 
Antimicrobials in Food Animals, section 2.3.5. Geneva: WHO. 
 Saenz, Y., Brinas, L., Dominguez, E., Ruiz, J., Zarazaga, M., Vila, J. and Torres, C. (2004). 
Mechanisms of resistance in multiple-antibiotic-resistant Escherichia coli strains of 
human, animal, and food origins. Antimicrob Agents Chemother 48:3996–4001. 
Salehzadeh, F., Madani, R.., Salehzadeh, A., Rokni, N. and Golchinefar, F. (2006). 
Oxytetracycline Residue in Chicken Tissues from Tehran Slaughterhouses in Iran. 
Pakistan Journal of Nutrition 5 (4): 377-381. 
Salyer, A.A. and Shoemaker N.B. (1997). Conjugative Transporting. Genet. Eng. 19: 89–99. 
Sarmah, A. K., Meyer, M.T., and Boxall, A.B.A. (2006). A global perspective on the use, 
sales, exposure pathways, occurrence, fate and effects of veterinary antibiotics (VAs) 
in the environment. Chemosphere 65: 725–759. 
Sasanya, J.J, Ogwal Okeng, J. Ejobi, F. Muganwa, M, 2005. Use of sulfonamides in layers in 
Kampala district, Uganda and sulfonamide residues in commercial eggs. Faculty of  
Veterinary Medicine, Makerere University. Afr Health Sci. 5(1): 33–39. 
Schmidt R.H., Rodrick G.E. (2003). Food Safety Handbook. John Wiley and Sons, New 
Jersey: pp312-313. 
Schroeder, C., Meng, J., Zhao, S., Debroy, C., Torcolini, J., Zhao, C., Mcdermott, P.F., 
Wagner, D.D., Walker, R.D. and White, D.G. (2002). Antimicrobial resistance of 
Escherichia coli O26, O103, O111, O128 and O145 from animals and humans. Emerg 
Infect Dis 8:1409-1414. 
Schwartz, M. H. and Sher, T. H. (1984). Anaphylaxis to penicillin in a frozen dinner. Ann. 
Allergy 52:342-343 
Schwarz, S. and Chaalus-Dancla, E. (2001). Use of antimicrobials in veterinary medicine and 
mechanisms of resistance. Vet. Res. 32: 201-225.  
Seprer, C.E Top, M contuner and M. mergeay, (1999). The human-flora-associated (HFA) 
mice model. Regul. Toxicol.Pharmacol. 34:125-136. 
Settepani, J. A. (1984). The hazard of using chloramphenicol in food animals. J. Am. Vet. 
Med. Assoc. 184, 930-931. 
Seyfarth, A. M., Wegener, H. C. and Frimodt-Moller, N. (1997). Antimicrobial resistance in 
Salmonella enterica subsp. enterica serovar typhimurium from humans and 
production animals. J Antimicrob Chemother 40:67–75. 
Shaib, B.A., A. Aliyu and J. S. Bakshi. (1997). Nigerian National Agricultural Research 
Strategy Plan: 1996–2010. Federal Department of Agricultural Sciences, Federal 
Ministry of Agriculture and Natural Resources, Abuja, Nigeria, 
Shaikh, B. and Allen, E. H. (1985). Overview of physical-chemical methods for determining 
aminoglycoside antibiotics in tissues and fluids of food-producing animals. J. Assoc. 
Off. Anal. Chem. 68:1007-1013. 
Shaikh, B. and Moats, W.A. (1993). Liquid-chromatographic analysis of antibacterial drug 
residues in food-products of animal origin. Journal of Chromatography 643:369–
378. 
Shareef, A. M., Jamel, Z. T. and Yonis, K. M. (2009). Detection of antibiotic residues in 
stored poultry products.Iraqi Journal of Veterinary Sciences. 23:S45-S48. 
Sherrat, D. (1989) In and related transposable Elements. In D.E. Berg and M.M. Howl. Eds. 
Mobile. DNA Washington. D.C. American Society for Microbiology: 163 – 184.  
Shitandi, A. and Sternesjö, Å. (2001). Detection of antmicrobial drug residues in Kenyan 
milk. J. Food Safety 21:205-214. 
Siegel, B.B. (1959). Hidden Contacts with penicillin. Bull of world health Organization 21: 
703-713. 
Simonsen, S. Tapsall, J.W, Tabot E. and Lazzari S. (2007). The Antimicrobial Resistance 
Containment and Surveillance Approach – a public health tool. Bull. WHO 82: 928-
934. 
Sofos, J.N. (2008). Challenges to meat safety in the 21st century. Meat Sci 78:3-13 
Soggard, H. (1973): Incidence of Drug Resistance and Transmissible R Factor in Strains of E. 
Coli Isolated from Feaces of Healthy Pigs. Actavetrinariascandinarica, 14:381 – 391. 
Sonaiya E. B. and Swan S. E. J. (2004) Small-scale Poultry Production. FAO Tecnical guide 
60pp 
Sonaiya, E.B. (ed). (1990). Rural Poultry in Africa. Proceedings of an international workshop 
held on November 13-16, 1989 at Obafemi Awolowo University, Ile-Ife, Nigeria. Ile-
Ife:ANRPD, 266 pp 
Speedy, A.W. (2003). Global production and consumption of animal source foods. J. Nutr. 
133:4048-4053. 
Spoo, J. W. (1995). Tetracycline antibiotics. In: Adams, R. H. (ed.) Veterinary Pharmacology 
and Therapeutic., 7th ed. Iowa State University press, Ames, Iowa, USA, pp.784-796. 
Stark, J. (2000). Antibiotika – nachweis in fleisch (Antibiotics - detectable in meat; Meat 
Industry). Fleischwirtschaft 80:46–50. 
Stead, S., Sharman, M., Tarbin, J.A., Gibson, E., Richmond, S., Stark, J. and Geijp, E. 
(2004). Meeting maximum residue limits: An improved screening technique for the 
rapid detection of antimicrobial residues in animal food products. Food Additives and 
Contaminants 21:216–221. 
Sternesjö, Å. and Johnsson, G. J. (1998). A novel rapid enzyme immunoassay (Fluorophos 
BetaScreen) for detection of beta-lactam residues in ex-farm raw milk. J. Food. 
Prot. 61, 808-811. 
Stokes, H.W. & Hall, R.M.  (1989).  A novel family of potentially mobile DNA elements 
encoding site-specific gene-integration functions: integrons. Molecular 
Microbiology 312. 1669–1683. 
Stowe, M., Terhune, D. and Wlmore P. (1980). A survey of use and misuse of tetracyclines. 
USA, Animal Health Meeting  81: 331-338. 
Su, J., Shi, L., Yang, L., Xiao, Z. Li, X. and Yamasaki, S. (2006). Analysis of integrons in 
clinical isolates of Escherichia coli in China during the last six years. FEMS 
Microbiol. Lett. 254:75–80. 
Sullivan, Å., Edlund, C. and Nord, C.E. (2001). Effect of antimicrobial agents on the 
ecological balance of human microflora. Lancet Infect. Dis.1:101-114. 
Sunde, M., and Nordstrom, M. (2006). The prevalence of, associations between and conjugal 
transfer of antibiotic resistance genes in Escherichia coli isolated from Norwegian 
meat and meat products. J. Antimicrob. Chemother. 58:741–747. 
Sundin G.W. (2003): Tetracycline. Encyclopedia of Agrochemicals. John Wiley & Sons, 
New Jersey: 1521–1522. 
Sundlof, S. F., Fernandez, A. H., Paige, J. C. (2000) Antibiotic Residues in Food Producing 
Animals. In: Antimicrobial Therapy in Veterinary Medicine. Prescott JF, Baggot 
RD, Walker RD (ed): 3rd Edition: Iowa State University Press, USA. pp 744-759. 
Swann, M.M., Baxter, K.L. and Field, H.I. (1969). Report of the Joint Committee on the Use 
of Antibiotics in Animal Husbandry and Veterinary Medicine. Published by Her 
Majesty Stationery Office (HMSO) London, CMnd 4190. 
Swartz, M. (2002). Human diseases caused by food-borne pathogens of animal origin. 
Clinical Infectious Diseases 34:111–122. 
Thielman N.M. and Guerrant R.L. (1999). Escherichia coli. In: Yu VL, Merigan, Jr. TC, 
Barriere SL eds. Antimicrobial therapy and vaccines. The Williams and Wilkins 
Company, Baltimore, Md, Pp. 188-200. 
Thomas, C.M. (2000). Paradigm, of Plasmid Organization. Mol Microbiol 37:485-491 
Threlfall, E. J., L. R. Ward, J. A. Frost, and G. A. Willshaw. (2000). The emergence and 
spread of antibiotic resistance in food-borne bacteria. Int J Food Microbiol 62:1–5. 
Timoney, J.F., Gillespie, J.H. Scott F.W. and Barlough J.K. (1988). The genetics of virulence 
and antibiotic resistance. In: Hagan and Bruner’s Microbiology and infectious 
diseases of domestic animals. 8th ed. Cornell University Press, Ithaca and London 
Pp.24-32. 
Tinkelman D.G., Bock S.A. (1984). Anaphylaxis presumed to be caused by beef containing 
streptomycin. Ann Allergy 53:243-244. 
Toldra, F. and Reig, M. (2006). Rapid detection of chemical and veterinary drug residues in 
animal foods. Trends Food Sci Techn 17:482-489. 
Turtura G.C., Massa S., Chazvinizadeh H. (1990). Antibiotic resistance among coliform 
bacteria isolated from carcasses of commercially slaughtered chickens. Int. J. of Food 
Microbiol.11: 351–4. 
Udoh, E. J. and Akintola, J. O. (2002). An analysis of beef demand in a Nigerian urban city. 
Global Journal of Pure and Applied Sciences. 9: 7-12. 
Umolu P.I., Ohenhen E. R., Okwu I. G., Ogiehor I. S. (2006). Multiple Antibiotics Resistant 
Index and Plasmid of Escherichia coli in Beef in Ekpoma. J. Am. Sci. 2(3): 22-28. 
US-FDA. (1996). United States Food and Drug Administration. Microbiological testing of 
antimicrobial drug residues in food, U.S. Food and Drug Administration, Center for 
Veterinary Medicine Guideline no. 52. 
Valla, S. (1998). Broad host-range plasmids and their role in gene transfer in nature. APMSIS. 
Suppl.  84:19-24 
van den Bogaard, A.E., London, N. and Driessen, C. (1998). The effect of antimicrobial 
growth promoters on the resistance in faecal indicator bacteria of pigs. Proceedings of 
th
the 38  Interscience Conference on Antimicrobial Agents and Chemotherapy; San 
Diego, Sep 24-7 1998 
Van den Bogaard, A.E. and Stobberingh, E.E. (1999). Antibiotic usage in animals: impact on 
bacterial resistance and public health. Drugs 58, 589-607. 
Van den Bogaard, A.E. and Stobberingh, E.E. (2000). Epidemiology of resistance to 
antibiotics. Links between animals and humans. Intl J Antimicrob Agents 14:327-335. 
Van Dresser W. R. and Wilcke J. R. (1989). Drug residues in food animals. J Am Vet Med 
Assoc 194:1700–1710 
Van Miert, A.S. (1990). Veterinary drugs and good veterinary practice. Tijdschr 
Diergeneeskd 115:125-31 
Vining, L.C. (1990). Functions of Secondary Metabolities. Ann. Rev. Microbiol: 44:395-427. 
Vollaard, E.J. and Claesner, H.A.L. (1994). Colonization resistance. Antimicrob Agents 
Chemother 38:409-414. 
Von Baum, H., and Marre, R. (2005). Antimicrobial resistance of Escherichia coli and 
therapeutic implications. Int J Med Microbiol 295:503–511. 
Waksman, S.A. and Woodruff, H.B. (1942). Streptothricin; A New Selective Bacteria Static 
and bacteriocidal Agent; Particularly Active against Gram-negative Bacteria. Proc. 
Soc. Exper. Biol. Med 49: 207-210. 
Waltner-Toews, D. and McEwen, S. (1994). Residues of antibacterial and antiparasitic drugs 
in food of animal origin: a risk assessment. Prev. Vet. Med. 20:219-234. 
Webber, M. & Piddock, L.J.V. (2001). Quinolone resistance in Escherichia coli. Veterinary 
Research 32: 275–284. 
Wegener, H. C., Aarestrup, F. M., Gerner-Smidt, P. and Bager, F. (1999). Transfer of 
antibiotic resistant bacteria from animals to man. Acta Veterinaria Scandinavica 92: 
S51–S57 
White D.G. Zhao S., Singh, R. and McDermott, P.F. (2004). Antimicrobial resistance among 
gram-negative foodborne bacterial pathogens associated with foods of animal origin. 
Foodborne Patho. Dis 1:137-152. 
Willshaw, G.A., Smith, H.R. and Roberts, D., (1993). Examination of raw beef products for 
the presence of Vero cytotoxin producing E coli, particularly those of serogroup 
O157. J Appl Bacteriol 75: 420-42 
Wise, R., Hart, T. Cars, O. Streulens, M. Helmuth, R. Huovinen P. and Sprenger M. (1998). 
Antimicrobial resistance is a major threat to public health. BMJ; 317: 609-10  
Witte, W. (1998). Medical consequences of antibiotic use in agriculture. Science 279:996-997 
Woodward, K.N. (1991). Hypersensitivity in humans and 628 exposure to veterinary drugs. 
Vet. 629 Toxicol., 33, 168-172. 
Woodward, K. N. (1998). The use of microbiological end-points in the safety evaluation and 
elaboration of maximum residue limits for veterinary drugs intended for use in food 
producing animals. Vet Pharmacol Ther 21:47-53. 
World Health Organization -WHO (1988). Joint FAO/WHO Expert Committee on Food 
Additives (JECFA). Toxicological evaluation of certain veterinary drug residues in 
food: Monograph prepared by the thirty-second meeting of the Joint FAO/WHO 
Expert Committee on Food Additives. WHO Technical Report Series, No. 763. 
WHO, Geneva. 
World Health Organization -WHO (1991). Joint FAO/WHO Expert Committee on Food 
Additives (JECFA). Toxicological evaluation of certain veterinary drug residues in 
food: Monograph prepared by the thirty-sixth meeting of the Joint FAO/WHO 
Expert Committee on Food Additives. WHO Technical Report Series, No. 815. 
WHO, Geneva. 
World Health Organization -WHO (2000). Global principles for the containment of 
antimicrobial resistance in animals intended for food. Report of a WHO Consultation 
with FAO and OIE. Geneva, Switzerland, 5–9 June 2000. 
WHO/CDS/CSR/APH/2000.4. http://www.who.int/emc 
Wray, C. (1997). Medical impact of antimicrobial use in food animal production: scenarios 
and risk assessment Salmonella and E. coli in England and Wales. Proceedings of the 
WHO Meeting on the Usage of Quinolones in Animals. 1997Oct 13-7; Berlin. 
Wray, C., Davies, R.H. and Corkish, J.D. (1996). Enterobacteriaceae. In F.T.W. Jordan and 
M. Pattison (Eds.), Poultry Diseases 4th edition Pp 9–43 London: Saunders Company 
Ltd. 
Zhao, S., White, D.G. Ge, B. Ayers, S. Friedman, S. English, L. Wagner, D. Gaines, S. and 
Meng, J. (2001). Identification and characterization of integron-mediated antibiotic 
resistance among Shiga toxin-producing Escherichia coli isolates. Appl Environ. 
Microbiol 67:1558-1564. 
Zhao, S., Maurer, J.J., Hubert, S., De Villena, J.F., McDermott, P.F., Meng, J., Ayers, S., 
English, L. and White, D.G. (2005). Antimicrobial susceptibility and molecular 
characterization of avian pathogenic Escherichia coli isolates. Vet Microbiol 107:215-
24. 
 
 
 
 
 
 
 
 
 
 
APPENDIXES 
Appendix i: Codex Definitions on antibiotics and residue 
Acceptable Daily Intake (ADI): An estimate by JECFA of the amount of a veterinary drug, 
expressed on a body weight basis, that can be ingested daily over a lifetime without 
appreciable health risk (standard man = 60 kg). 
Bioavailable Residues: Those residues that can be shown, by means of an appropriate 
method (e.g. Gallo-Torres method) to be absorbed into systemic circulation when fed to 
laboratory animals. 
Bound Residue: This is a residue derived from the covalent binding of the parent drug or a 
metabolite of the drug and a cellular biological soluble or insoluble macromolecule. These 
residues are not extractable from the macromolecule by exhaustive extraction, denaturation or 
solubilization techniques. They do not result from the incorporation of metabolized, 
radiolabelled fragments of the drug into endogenous compounds, or the same macromolecule 
by normal biosynthetic pathways. 
 
Egg: The fresh edible portion of the spheroid body produced by female birds, especially 
domestic fowl. The edible portions of the egg include the yolk and egg white after removal of 
the shell. 
Extractable Residue: Those residues extracted from tissues or biological fluids by means of 
aqueous acidic or basic media, organic solvents and/or hydrolysis with enzymes (e.g. 
sulfatase or glucuronidase) to hydrolyze conjugates. The extraction conditions must be such 
that the compounds of interest are not destroyed 
Good Practice in the Use of Veterinary Drugs (GPVD): Is the official recommended or 
authorized usage including withdrawal periods, approved by national authorities, of 
veterinary drugs under practical conditions. The maximum residue limit for veterinary drugs 
(MRLVD) can be assured with good practice in the use of veterinary drugs. Good Veterinary 
Practice of antimicrobial products is the rational antibacterial therapy which is based on a 
combination of clinical judgement, laboratory diagnosis, clinical knowledge, epidemiological 
background and husbandry information about the flock to be treated. The usage of 
antimicrobials should not replace fundamental shortcomings in husbandry, biosecurity 
measures and prophylactic hygiene. The administration of antimicrobial products in disease 
situations is supposed to be complimented with good farm management and properly-
designed immunization programs. 
Marker Residue: A residue whose concentration decreases in a known relationship to the 
level of total residues in tissues, eggs, milk or other animal tissues. A specific quantitative 
analytical method for measuring the concentration of the residue with the required sensitivity 
must be available. 
Maximum Residue Limit for Veterinary Drugs (MRLVD): Is the maximum concentration 
of residue resulting from the use of a veterinary drug (expressed in mg/kg or µg/kg on a fresh 
weight basis) that is recommended by the Codex Alimentarius Commission to be legally 
permitted or recognized as acceptable in or on a food. It is based on the type and amount of 
residue considered to be without any toxicological hazard for human health as expressed by 
the Acceptable Daily Intake (ADI), or on the basis of a temporary ADI that utilizes an 
additional safety factor. It also takes into account other relevant public health risks as well as 
food technological aspects. When establishing an MRL, consideration is also given to 
residues that occur in food of plant origin and/or the environment. Furthermore, the MRL 
may be reduced to be consistent with good practices in the use of veterinary drugs and to the 
extent that practical analytical methods are available. 
Meat: The edible part of any mammal. 
Milk : Milk is the normal mammary secretion of milking animals obtained from one or more 
milkings without either addition to it or extraction from it, intended for consumption as liquid 
milk or for further processing. 
 Muscle: Muscle is the skeletal tissue of an animal carcass or cuts of these tissues from an 
animal carcass that contains interstitial and intramuscular fat. The muscular tissue may also 
include bone, connective tissue, tendons as well as nerves and lymph nodes in natural 
portions. It does not include edible offal or trimmable fat.  
Non-Extractable Residues: These residues are obtained by subtracting the extractable 
residues from the total residues and comprise: 
i) Residues of the drug incorporated through normal metabolic pathways into 
endogenous compounds (e.g. amino acids, proteins, nucleic acid). These residues are 
of no toxicological concern.  
ii) Chemically-bound residues derived by interaction of residues of parent drug or its 
metabolites with macromolecules. These residues may be of toxicological concern  
Poultry: Means any domesticated bird including chickens, turkeys, ducks, geese, guinea-
fowls or pigeons.  
Regulatory Method of Analysis: A method that has been legally enacted and/or validated in 
a multi-laboratory study and can be applied by trained analysts using commercial laboratory 
equipment and instrumentation to detect and determine the concentration of a residue of a 
veterinary drug in edible animal products for the purpose of determining compliance with the 
MRL.  
Residues of Veterinary Drugs: Include the parent compounds and/or their metabolites in 
any edible portion of the animal product, and include residues of associated impurities of the 
veterinary drug concerned.  
Screening Method: This is a rapid, relatively inexpensive, and rugged field method used for 
testing for a specific substance or closely related group of substances which are sufficiently 
selective and sensitive to allow at least semi-quantitative detection of residues in contents in 
accordance with the established maximum limit.  
Temporary Acceptable Daily Intake (TADI): Used by JECFA when data are sufficient to 
conclude that use of the substance is safe over the relatively short period of time required to 
generate and evaluate further safety data, but are insufficient to conclude that use of the 
substance is safe over a lifetime. A higher-than-normal safety factor is used when 
establishing a temporary ADI and an expiration date is established by which time appropriate 
data to resolve the safety issue should be submitted to JECFA.  
Tissue: All edible animal tissue, including muscle and by-products.  
Tissue, Control: Tissue from animals not treated with veterinary drugs of the same species, 
sex, age and physiological status as the target species.  
Tissue, Dosed: Tissue from animals of the test species that have been treated with the drug 
according to its intended use.  
Tissue, Spiked or Fortified: Tissue containing known concentrations of the analyte added to 
the sample of control tissue.  
Total Residue: The total residue of a drug in animal derived food consists of the parent drug 
together with all the metabolites and drug based products that remain in the food after 
administration of the drug to food producing animals. The amount of total residues is 
generally determined by means of a study using the radiolabelled drug, and is expressed as 
the parent drug equivalent in mg/kg of the food.  
Validated Method: This is an analytical method which has been subjected to a multi-
laboratory study for accuracy, precision, reproducibility performance and ruggedness. 
Concise written procedures for sample selection, preparation and quantitative analysis are 
provided for inter-laboratory quality assurance and consistency of results, on which an 
appropriate regulatory method of analysis can be established.  
Veterinarian Client-Patient Relationship: The relationship is recognized when the 
livestock enterprise, premises and husbandry practices are known to the veterinarian as a 
result of a recent professional visit to the site and the veterinarian is available for emergency 
on site consultation and is responsible for preventative medicine programmes.  
Veterinary Drug: Any substance applied or administered to any food-producing animal, 
such as meat or milk producing animals, poultry, fish or bees, whether used for therapeutic, 
prophylactic, or diagnostic purposes, or for modification of physiological functions or 
behaviour. 
Withdrawal Time and Withholding Time: This is the period of time between the last 
administration of a drug and the collection of edible tissue or products from a treated animal 
that ensures the contents of residues in food comply with the maximum residue limit for this 
veterinary drug (MRLVD).  Meat and eggs must be withheld from human consumption until 
residues are depleted below the tolerance limits set by the authorities. Withdrawal periods, 
ranging from a few days to a few weeks vary according to the drug used, dosage, route of 
administration, and animal species and are defined as the time required for 99% of the 
animals in a population (treated according to label instructions) to be free of drug residues 
above the tolerance level.  
Appendix IIa: QUESTIONNAIREs ON ANTIBIOTICS USAGE IN FOOD ANIMALS
  IN NIGERIA (cattle) 
UNIVERSITY OF IBADAN 
DEPARTMENT OF VETERINARY PUBLIC HEALTH AND PREVENTIVE 
MEDICINE 
QUESTIONNAIRE ON ANTIBIOTICS USAGE IN CATTLE IN NIGERIA 
Dear Respondents, 
This questionnaire survey is an academic exercise on the use of antibiotics in food animal 
(especially poultry and cattle) production in Nigeria. All information supplied will be treated 
with utmost confidentiality and used for research only.  
Thank you for your time and cooperation. 
(A)  CATTLE OWNERS BACKGROUND INFORMATION 
1. Age: 10-20 ( )   21-30 ( ) above 30 ( ) 
2. Educational level: primary ( ) secondary ( ) tertiary ( ) others specify…. 
3. Location of the farm (Local Government Area)……  
(B) PRODUCTION DATA 
1. Types of farming system: Intensive ( ) Extensive ( )   Semi intensive ( ) 
2. Population of the herd 1-5 ( ) 5-10 ( ) 11-20 ( ) above 20 ( ) 
3. Nature of the herd: Calves (# =), Heifers (# =), Bull (# =), Cow (# =) 
4. Purpose of production; Milk ( ) Meat ( ) Draft ( ) 
5. Breeds of cattle:  White Fulani/Bunaji ( ) Ndama ( ) Sokoto Gudali ( ) Kuri ( ) Others 
………… 
6. Years of experience in cattle production: 1-5 years ( ) 5-10 years ( ) above 10 years ( ) 
 
(C) FEEDS AND FEEDING 
1. What do you feed the animals on? Commercial feed and concentrate ( ) Pasture ( )both ( ) 
2. Source of feed: Self milled ( ) Commercial milled ( )  
3. Do you use drug as feed additives? Yes ( )  No ( ) 
4. If yes state the particular drugs ………………………………………………………. 
5. Why do use it? 
(D) CATTLE DISEASES AND HEALTH 
1. Tick the common symptoms of cattle disease you observed? 
Diarrhea ( ) Wound/Abscess ( ) Nasal discharge ( ) Coughing ( ) Weight loss ( ) 
lameness/foot Rot ( ) Mouth lesion/salivation ( ) 
2. What is the average mortality? This month ( ) this week ( ) Yesterday ( ) 
3. How do you diagnose disease on the farm? Through clinical signs ( ) mortality ( ) post 
mortem findings ( ) laboratory findings ( ) 
4. Who does the diagnoses and treatment of disease on the farm? Vet doctors ( ) animal 
health officer ( ) self by experience ( ) others ( ) 
5. Do you do laboratory test before treatment? Yes ( )  No ( ) 
6. Do you always follow the manufacturer‟s instruction on drug use? Most often ( ) often ( ) 
never ( ) 
7. State your reasons? ............................................................................................... 
(E) DISEASES TREATMENT AND PREVENTION 
1. Do you use antibiotics for preventive purpose? Yes ( ) No ( ) 
2. If yes to what extent?  Very often ( ) often ( ) rarely ( )   very rare ( ) 
3. Commonly used antibiotics: Oxtetracycline ( ) Penicillin ( ) Gentamycin ( ) Enrofloxacin ( 
) Neomycin ( ), Streptomycin ( ) others ( ) 
4. Source of the antibiotics: Manufacturers ( ) Manufacturer‟s representatives ( ) 
Vet/Agrochemical stores/shops ( ) Hawkers ( ) Feed mill ( )  
5. Do you rely on Veterinary Doctor for disease treatment? Yes ( )  No ( ) 
6. Do you observe the recommended withdrawal periods when using drugs? Yes ( ) no ( ) 
7. If yes, how…………… 
8. Do you know of any effect of drugs remains in cattle meat and milk? Yes ( )  no ( ) 
9. If yes, which one……………………………………………………………………. 
(F) POLICY 
1. Are you aware of any law on drug use in your animal? Yes ( )  No ( ) 
2. If yes which ones? …………………………………………………………………… 
3. Are these laws actively enforced by the necessary authorities? Not enforced ( ) 
Enforced regularly ( ) Enforced irregularly 
 
COMMENT 
Please comment freely on drug distribution and use in Nigeria. ……………………… 
…………………………………………………………………………………………………
………………………………………………………………………………………………... 
 
 
 
 
 
 
 
 
 
 
 
 
 
Appendix IIb: QUESTIONNAIRE ON ANTIBIOTICS USAGE IN POULTRY IN 
NIGERIA 
 
DEPARTMENT OF VETERINARY PUBLIC HEALTH AND PREVENTIVE 
MEDICINE, FACULTY OF VETERINARY MEDICINE UNIVERSITY OF 
IBADAN 
 Dear Respondent, 
This questionnaire is designed to assess the pattern of antibiotics usage in poultry industry. 
Please respond to the questions appropriately, your confidentiality is guaranteed. All 
information shall be used for academic purpose. 
Thank you for your time and cooperation. 
(A) FARM BACKGROUND INFORMATION 
  1. Respondent: Owner {  } worker {   } 
  2. Age: 21-25{  } 26-30{  } Above 30{   }  
  3. Education level: Primary {   } Secondary {   } OND {  } HND Graduate {   } others
 specify……………………………………….. 
  4. Location of the farm [Local Government Area] ………………………….   
(B) PRODUCTION DATA 
1. Type of Farming system Small Scale{   } Commercial {  } 
2. Management System:  Deep litters {   }    Battery cage  
3. Population of birds ……………………………………………………….  
4. Purpose of production: Chicken {  }   Egg {   }   Day old chicks {   } 
5. Types of birds: pullet {    } Cockerel {    } Broilers {    } 
(C) FEEDS AND FEEDING 
1. What is the source of your feeds? Self milled {    } Commercial feeds {   } 
2. Do you add drug[s] to your feed? Yes{   }  No{    } 
 3. If yes state the particular drug  
4. When do you use drug? When birds are sick {   } When mortality is recorded {   }To boost 
production {    } 
(D) POULTRY DISEASES AND HEALTH 
1.  What are the common poultry diseases you do encounter? 
i…………………………………. ii………………………………… 
iii………………………………… iv………………………………..  
v..……………………….. 
2. What is the average mortality? 
      This month {   } this week {   } Yesterday {   } 
3. How do you diagnose diseases on the farm? Through clinical signs{   }  
Mortality {   } post mortem findings {   } laboratory finding {   } 
4. Who does the diagnosis and treatment of disease on the farm? Vet Doctors {   } 
animal health officer {   } self/ by experience {   } others……………………………. 
5. Do you perform laboratory text before treatment? Yes {   } No{   } 
6. Do you always follow the manufacturer‟s instruction on the use of drug„s? Most often    
{   }Very often {   } often {   } never{   } 
7. State your reason(s) 
(E) TREATMENT 
1. Do you use antibiotics for preventive purpose? Yes {   } No {   } 
2. If yes to what extent? Very often {   } often {   } Rarely {   } very rare {   } 
3. Tick the common antibiotics you normally use oxytetracyline {   } Penicillin {   } 
Enroflaxacin {   } Neomycin {   } Gentamicin {   } others……………………………. 
4. Source of antibiotics; Vet. Shop {   } Feed mill {   } by farm vet. {   } 
5. Do you rely on vet to complete the dosage ?Yes {   } No {   } 
6. Do you observe any withdrawal period recommended by manufacturer when using 
antibiotics? Yes {   } No {   } 
7. If yes, How 
…………………………………………………………………………………………
……………….. 
8. Do you know of any effect of drug remains in chicken meat? Yes {   } No {   } 
9. If yes, which one......................................................................... 
 
 
 
 
 
Appendix IIIa: List of Respondent Poultry Farmers 
S/N Name and Location Average Flock Flock Type (L= 
Size Layers, B= 
Broilers) 
1 Abrahamsum Farms, Akure 10,000 L 
2 Adegoke Farms, Akure 15,000 L 
3 Ben-K Farms, Ikotun, Lagos 10,000 B 
4 Busyvice Farm, Agege, Lagos 8000 L & B 
5 Covenant Farm, Olodo, Ibadan 2,500 L 
6 December Farm, Igbesa, Lagos 40,000 L & B 
7 Dutel Farm, Ijaye, Lagos 25,000 L 
8 Fabak Farm, Agege, Lagos. 9,000 L 
9 Farm Support Services, Olodo, Ibadan 42,500 L 
10 Fomalko Farm, Agbowo, Ibadan 8,000 L 
11 Goodhealth Farm, Igbesa, Lagos 60,000 L & B 
12 Iloti Farm, Ikorodu, Lagos 20,000 B 
13 Jofa Farms, Akure 40,000 L& B 
14 Lazana Farms, Ojodu, Lagos 24,000 L 
15 Mirth Agric Farm, Asejire, Ibadan 35,000 L 
16 Mrs Ojo, (Principal) Farms, Akure 5,000 L 
17 Mustard Seed, Ojodu, Lagos 2,500 L 
18 New Earth Farm, Badagry, Lagos 20,000 L 
19 Ola Farms, Oko-Oba, Lagos 20,000 L & B 
20 Olabosco Farm, Igbesa, Lagos 62,500 L 
21 Ologun Farm, Ogudu, Lagos 5000 B 
22 Omotosho Farms, Lagos 1,500 L 
23 Providence Farms, Lagos 3,000 L 
24 Ritlab Farm, Ogba, Lagos 650 B 
25 S&S Farm, Epe, Lagos 10,000 L 
26 Sachel Farm, Badagry, Lagos 2,500 B 
27 Zartech Farms Ibadan 63,500 L & B 
28 Bronco Farms Oluyole, Ibadan 50,000 B 
29 Bamfot Farm, Ife-Rd, Ibadan 30,000 L 
30 Ola-Omolola Farms Ibadan 5,500 L 
 
 
 
 
Appendix IIIb: List of Respondent Cattle Producers 
S/N Name and Location Average Herd Size 
(heads of cattle) 
1 Ahaji Dauda Eleran, Oba Ile Akure. 82 
2 Alfa Mahamud, Akinsawe,yana Offa, Ibadan 34 
3 Alfa Mumin, Akinsawe,Iyana Offa, Ibadan 80 
4 Alfa Saheed, Akinsawe,Iyana Offa, Ibadan 28 
5 Alhaji Bala, Ojodu, Lagos 73 
6 Alhaji Bello, Akinsawe,Iyana Offa, Ibadan 120 
7 Deacon Bamidele, Oda-Road, Akure    35 
8 Alhaji Mohamed, Ayede, Egbeda, Ibadan 84 
9 Alhaji Tijani, Ayede, Egbeda, Ibadan 115 
10 Alhaji, Yekeeni  Ojodu, Lagos 77 
11 Dr Adejumo, Apata, Ibadan  24 
12 Mr Dauda Sheu, Bodija, Ibadan 26 
13 Mr Jamiu Lawal, Ojodu, Lagos 38 
14 Mr Raufu Junaidu, Bodija, Ibadan 45 
15 Mr Sule Lawal,  Akufo farm Ibadan 34 
16 Mr Sule, Ayede, Egbeda, Ibadan 86 
17 Mr Sunday Adedokun, Bodija, Ibadan  22 
18 Mr Sunday Adeniyi, Iddo road, Ologuneru, Ibadan. 40 
19 Mr Yusuf Taiwo Oko-Oba Lagos. 73 
20 Pastor Olusayo, Akinyele, Ibadan 48 
 
 
 
 
 
 
 
 
 
 
 
 
 
Appendix IV: Codex Alimentarius Commission Maximum Residue Limits for 
   Tetracylines (Chlortetracycline/Oxytetracycline/Tetracycline) in Foods 
 
Acceptable Daily Intake (group ADI for chlortetracycline, oxytetracycline and tetracycline): 
0-30 μg/kg body weight (50th JECFA, 1998).  
 
Species  Tissue MRL CAC 
(µg/kg) 
Cattle                                              M    u  s c  l e        2  0  0           26th (2003) 
Cattle                     Liver  600 26th (2003) 
Cattle                                              K   i d  n  e  y        1  2  0  0         26th (2003) 
Cattle                                              M    i l k            1  0  0           26th (2003) 
(μg/l) 
Fish Muscle 200 26th Applies only to 
(2003) oxytetracycline. 
Giant prawn (Paeneus Muscle 200 26th Applies only to 
monodon) (2003) oxytetracycline. 
Pig Muscle 200 26th (2003) 
Pig Liver 600 26th (2003) 
Pig Kidney 1200 26th (2003) 
Poultry Muscle 200 26th (2003) 
Poultry Liver 600 26th (2003) 
Poultry Kidney 1200 26th (2003) 
Poultry Eggs 400 26th (2003) 
Sheep Muscle 200 26th (2003) 
Sheep Liver 600 26th (2003) 
Sheep Kidney 1200 26th (2003) 
Sheep Milk 100 26th (2003) 
(μg/l) 
CAC/MRL 02-2009; JECFA Evaluation: 45 (1995); 47 (1996); 50 (1998); 58 (2002) 
 
 
 
 
 
 
 
 
 
Appendix v: Table of Number of samples required to detect at least one non-compliant 
result with pre-defined probabilities in a population having known non-compliance 
residue prevalence. 
Non-compliant Minimum number of samples required to detect a non-
prevalence (% in a compliant result with a confidence level of: 
population) 
90% 95% 99% 
35 6 7 11 
30 7 9 13 
25 9 11 17 
50 11 14 21 
15 15 19 29 
10 22 29 44 
5 45 59 90 
1 230 299 459 
0.5 460 598 919 
0.1 2302 2995 4603 
 
 
 
 
Appendix vi: Preparation of reagents and buffers 
a. 1N Hydrochloric Acid 
Molecular Formula = HCl;  % Purity  = 36%; Molar mass = 36.5 
Specific gravity  1180g/L 
Molarity    = % purity X Sp. gravity/100 X molar mass 
    =  36 X 1180/100 X36.5 
    = 11.64M 
M1V1    = M2V2 
V2     = M1V1/M2 
         = 1X1000/11.64 
         = 85.91ml 
85.91ml of concentrated HCl was added to distilled water and made up to 1000ml 
(1L) to obtain 1N HCl.  
b. 0.01M Oxalic acid 
Molar mass   = 126.07 
Molarity   = 0.01 
3   
g/dm  = 126.07 X 0.01 
    = 1.126g 
1.126g oxalic acid salt was dissolve in 1L of deionised water to make 0.01M solution. 
c.  Mobile Phase 
The mobile phase comprised of Methanol: Acetonitrile: 0.01M Oxalic acid 
(1:1.5:2.5). Using volumetric flask 200ml of methanol, 300ml of acetonitrile and 
500ml of 0.01oxalic acid were measured and mixed together to give 1000ml of the 
mobile phase in corked Duran‟s bottle. This was subsequently degassed in the 
ultrasonic water bath (sonicator) to release the dissolved gas. 
Methanol (HPLC grade) used as blank to flush the HPLC column was also degassed 
regularly in the sonicator.  
 
 
 
 
 
 
 
 
 
 
 
 
 
Appendix vii: Statistiscal Tables oxytetracycline residue in beef and chicken 
ANOVA table of Oxytetracycline residue in Akure beef 
 AkKD AkLD AkMD AkKW AkLW AkMW 
Number of 31 34 29 38 36 33 
values 
% 51.7 56.7 48.3 63.3 60.0 55.0 
Minimum 308.4 86.36 67.07 482.2 163.6 163.6 
25% 665.7 344.6 265 730.8 554.6 453.2 
Percentile 
Median 887.7 634.3 607.9 1139 940.8 549.8 
75% 1322 931.2 825.2 1530 1192 960.2 
Percentile 
Maximum 2770 1757 1187 2915 2544 1660 
Mean 1162 661.7 587.7 1185 945.2 692.6 
Std. 685.1 387 321.4 581.1 541.2 376.2 
Deviation 
Std. Error 123.1 66.36 59.69 94.27 90.19 65.49 
Lower 910.7 526.7 465.5 994 762.1 559.2 
95% CI of 
mean 
Upper 1413 796.7 710 1376 1128 826 
95% CI of 
mean 
Sum 36021 22497 17044 45029 34028 22855 
 
 
ANOVA table of Oxytetracycline residue in Lagos beef 
 LgKW LgLW LgMW LgKD LgLD LgMD 
Number of 34 30 29 36 36 31 
values 
% 56.7 50.0 48.3 60.0 60.0 51.7 
Minimum 76.7 163.6 178.1 308.4 240.8 67.1 
25% 948.3 646.3 453.2 1144 453.2 308.5 
Percentile 
Median 1243 815.3 694.6 1356 742.9 453.4 
75% 1429 1284 885.3 1733 863.6 646.5 
Percentile 
Maximum 2409 1708 1926 2819 1824 1709 
Mean 1267 904.9 729.6 1436 761.7 546.2 
Std. 476.4 421.4 374.3 554.1 375.6 373.8 
Deviation 
Std. Error 81.7 76.93 69.5 92.35 62.6 67.14 
Lower 95% 1100 747.6 587.2 1248 634.6 409.1 
CI of mean 
Upper 95% 1433 1062 871.9 1623 888.7 683.3 
CI of mean 
Sum 43067 27148 21157 51687 27420 16932 
 
ANOVA table of Oxytetracycline residue in Ibadan beef 
 IbKW IbLW IbMW IbKD IbLD IbMD 
Number of 44 37 34 35 32 28 
values 
% 73.3 61.7 56.7 58.3 53.3 46.7 
Minimum 598.1 163.6 211.9 163.6 110 67.1 
25% 1182 583.6 453.4 916.7 668 260.1 
Percentile 
Median 1419 815.3 680.3 1322 888 549.8 
75% 1689 1202 863.8 1805 1180 728.4 
Percentile 
Maximum 5059 2210 2790 3736 2191 1245 
Mean 1544 917.5 766.2 1354 949.5 555.8 
Std. 870.8 465.2 513.9 696.5 505.6 277.8 
Deviation 
Std. Error 131.3 76.48 88.13 117.7 89.38 52.5 
Lower 95% 1280 762.4 586.9 1115 767.2 448.1 
CI of mean 
Upper 95% 1809 1073 945.5 1594 1132 663.5 
CI of mean 
Sum 67956 33946 26051 47401 30384 15563 
 
ANOVA table of Oxytetracycline residue in Lagos and Ibadan chicken 
 IbCh IbCh IbCh Lfm IbChMfm LgCh LgCh LgCh LgCh 
Lmkt Mmkt Lmkt Mmkt Lfm Mfm 
Number of values 60 60 60 60 60 60 60 60 
Minimum 0 0 0 0 0 0 0 0 
25% Percentile 0 0 0 0 0 24 0 0 
Median 762 308 776.5 260 728.5 255.5 757.5 525.5 
75% Percentile 1202 660.5 1660 695 1129 743 1547 936 
Maximum 2626 1525 10880 2206 1901 1660 12811 5474 
Mean 775.4 410.8 1232 438.6 642 437.9 1533 916.5 
Std. Deviation 687.9 428.9 1855 469.2 570.5 426.6 2590 1455 
Std. Error 88.8 55.38 239.4 60.58 73.66 55.07 334.4 187.8 
Lower 95% CI of mean 597.7 300 753.4 317.4 494.6 327.7 863.8 540.7 
Upper 95% CI of mean 953.1 521.6 1712 559.8 789.3 548.1 2202 1292 
Sum 46524 24646 73949 26315 38517 26273 91978 54988 
Tukey's Multiple Comparison Test (chicken) 
Tukey's Multiple Mean Diff. q P 95% CI of diff 
Comparison Test value 
IbCh Lmkt vs LgCh Lfm -757.6 4.492 P < 0.05 -1492 to -23.42 
IbCh Mmkt vs IbCh Lfm -821.7 4.873 P < 0.05 -1556 to -87.57 
IbCh Mmkt vs LgCh Lfm -1122 6.655 P < 0.001 -1856 to -388.1 
IbCh Lfm vs IbChMfm 793.9 4.708 P < 0.05 59.75 to 1528 
 IbCh Lfm vs LgCh Mmkt 794.6 4.712 P < 0.05 60.45 to 1529 
IbChMfm vs LgCh Lfm -1094 6.49 P < 0.001 -1829 to -360.2 
LgCh Lmkt vs LgCh Lfm -891 5.284 P < 0.01 -1625 to -156.9 
LgCh Mmkt vs LgCh Lfm -1095 6.494 P < 0.001 -1829 to -360.9 
 
 
 
Tukey's Multiple Comparison of Mean Oxytetracycline residue Test (beef) 
Parameter Comparison Mean Diff. Q P value 95% CI of diff 
 * AkKD vs AkMD 574.2 6.018 P < 0.01 80.37 to 1068 
  *AkKD vs AkLD 500.3 5.454 P < 0.05 25.55 to 975.0 
 * AkKD vs AkMD 574.2 6.018 P < 0.01 80.37 to 1068 
  AkLD vs IbLD -287.8 3.164 P > 0.05 -758.7 to 183.0 
  AkMD vs AkMW -104.8 1.115 P > 0.05 -591.4 to 381.7 
  AkMD vs LgMD 41.54 0.4354 P > 0.05 -452.3 to 535.4 
  AkMD vs IbMD 31.9 0.326 P > 0.05 -474.6 to 538.4 
  AkKW vs AkKD 23.03 0.2576 P > 0.05 -439.6 to 485.7 
 * AkKW vs AkMW 492.4 5.602 P < 0.05 37.54 to 947.3 
  AkKW vs LgKW -81.7 0.937 P > 0.05 -533.0 to 369.6 
  AkKW vs IbKW -35950% 440% P > 0.05 -782.8 to 63.87 
  *AkKD vs AkLD 500.3 5.454 P < 0.05 25.55 to 975.0 
  *AkKD vs AkMD 574.2 6.018 P < 0.01 80.37 to 1068 
  AkKD vs AkKW -23.03 0.2576 P > 0.05 -485.7 to 439.6 
  AkKD vs LgKD -273.8 3.025 P > 0.05 -742.2 to 194.6 
  AkKD vs IbKD -192.4 2.112 P > 0.05 -663.9 to 279.1 
  AkLD vs AkMD 73.95 0.792 P > 0.05 -409.3 to 557.2 
  AkLD vs AkLW -283.6 3.21 P > 0.05 -740.7 to 173.6 
  AkLD vs LgLD -99.98 1.132 P > 0.05 -557.1 to 357.2 
  AkLD vs IbLD -287.8 3.164 P > 0.05 -758.7 to 183.0 
  AkMD vs AkMW -104.8 1.115 P > 0.05 -591.4 to 381.7 
  AkMD vs LgMD 41.54 0.4354 P > 0.05 -452.3 to 535.4 
  AkMD vs IbMD 31.9 0.326 P > 0.05 -474.6 to 538.4 
  AkKW vs AkLW 239.7 2.791 P > 0.05 -204.9 to 684.4 
  *AkKW vs AkMW 492.4 5.602 P < 0.05 37.54 to 947.3 
  AkKW vs LgKW -81.7 0.937 P > 0.05 -533.0 to 369.6 
  AkKW vs IbKW -359.5 4.395 P > 0.05 -782.8 to 63.87 
  AkLW vs AkMW 252.7 2.838 P > 0.05 -208.0 to 713.4 
  AkLW vs LgLW 40.3 0.4413 P > 0.05 -432.3 to 512.9 
  AkLW vs IbLW 27.77 0.3212 P > 0.05 -419.8 to 475.3 
  AkMW vs LgMW -37 0.3935 P > 0.05 -523.6 to 449.6 
  AkMW vs IbMW -73.65 0.8159 P > 0.05 -540.8 to 393.5 
  LgKW vs LgLW 361.8 3.91 P > 0.05 -117.1 to 840.6 
  *LgKW vs LgMW 537.1 5.753 P < 0.05 53.91 to 1020 
  LgKW vs LgKD -169.1 1.914 P > 0.05 -626.2 to 288.1 
  LgKW vs IbKW -277.8 3.293 P > 0.05 -714.3 to 158.7 
  LgLW vs LgMW 175.4 1.823 P > 0.05 -322.5 to 673.2 
  LgLW vs LgLD 143.3 1.569 P > 0.05 -329.3 to 615.9 
  *LgLW vs IbKW -639.5 7.312 P < 0.001 -1092 to -186.9 
  LgLW vs IbLW -12.53 0.1381 P > 0.05 -482.2 to 457.1 
  LgMW vs LgMD 183.4 1.922 P > 0.05 -310.5 to 677.2 
  LgMW vs IbMW -36.65 0.3926 P > 0.05 -519.9 to 446.6 
 * LgKD vs LgLD 674.1 7.743 P < 0.001 223.5 to 1125 
 * LgKD vs LgMD 889.6 9.829 P < 0.001 421.2 to 1358 
  LgKD vs IbKD 81.44 0.9288 P > 0.05 -372.4 to 535.2 
  LgLD vs IbLD -187.8 2.093 P > 0.05 -652.3 to 276.6 
  LgMD vs IbMD -9.644 0.1001 P > 0.05 -508.0 to 488.8 
  *IbKW vs IbMW 778.2 9.227 P < 0.001 341.7 to 1215 
  IbKW vs IbKD 190.1 2.273 P > 0.05 -242.8 to 623.1 
  IbLW vs IbMW 151.2 1.724 P > 0.05 -302.9 to 605.4 
  IbLW vs IbLD -32.04 0.3593 P > 0.05 -493.5 to 429.4 
  IbMW vs IbMD 210.4 2.232 P > 0.05 -277.5 to 698.2 
  IbKD vs IbLD 404.8 4.481 P > 0.05 -62.73 to 872.4 
  *IbKD vs IbMD 798.5 8.526 P < 0.001 313.8 to 1283 
  IbLD vs IbMD 393.7 4.119 P > 0.05 -101.0 to 888.4 
Key: * significant difference  
IbKd = Ibadan Kidney (dry season); IbMd = Ibadan Muscle (dry season); IbLd = Ibadan Liver (dry season), IbKw = Ibadan Kidney (wet 
season) ; IbMw = Ibadan Muscle (wet season); IbLw = Ibadan Liver (wet season) 
AkKd = Akure Kidney (dry season); AkMd = Akure Muscle (dry season); AkLd = Akure Liver (dry season), AkKw = Akure Kidney (wet 
season); AkMw = Akure Muscle (wet season); AkLw = Akure Liver (wet season) 
LgKd = Lagos Kidney (dry season); LgMd = Lagos Muscle (dry season); LgLd = Lagos Liver (dry season), LgKw = Lagos Kidney (wet 
season); LgMw = Lagos Muscle (wet season); LgLw = Lagos Liver (wet season) 
Tukey's Multiple Comparison Test of oxytetracycline residue in chicken (Ibadan and Lagos) 
Tukey's Multiple Comparison Test Mean Diff. Q P value 95% CI of 
diff 
 *IbCh Lmkt vs IbCh Mmkt 426.6 5.528 P < 0.01 90.29 to 
763.0 
 IbCh Lmkt vs IbCh Lfm -169.7 2.227 P > 0.05 -501.9 to 
162.5 
 *IbCh Lmkt vs IbCh Mfm 419.2 5.467 P < 0.01 85.02 to 
753.4 
 IbCh Lmkt vs LgCh Lmkt 90.32 1.218 P > 0.05 -232.9 to 
413.5 
 *IbCh Lmkt vs LgCh Mmkt 402.2 5.476 P < 0.01 82.08 to 
722.4 
 IbCh Lmkt vs LgCh Lfm -143.8 1.929 P > 0.05 -468.7 to 
181.0 
 IbCh Lmkt vs LgCh Mfm 233.7 3.007 P > 0.05 -104.9 to 
572.3 
 *IbCh Mmkt vs IbCh Lfm -596.3 8.072 P < 0.001 -918.3 to -
274.4 
 IbCh Mmkt vs IbCh Mfm -7.421 0.09979 P > 0.05 -331.5 to 
316.7 
 *IbCh Mmkt vs LgCh Lmkt -336.3 4.687 P < 0.05 -649.1 to -
23.58 
 IbCh Mmkt vs LgCh Mmkt -24.43 0.3439 P > 0.05 -334.0 to 
285.1 
 *IbCh Mmkt vs LgCh Lfm -570.5 7.907 P < 0.001 -884.9 to -
256.0 
 IbCh Mmkt vs LgCh Mfm -193 2.559 P > 0.05 -521.6 to 
135.6 
 *IbCh Lfm vs IbCh Mfm 588.9 8.027 P < 0.001 269.2 to 
908.7 
 IbCh Lfm vs LgCh Lmkt 260 3.676 P > 0.05 -48.22 to 
568.3 
 *IbCh Lfm vs LgCh Mmkt 571.9 8.172 P < 0.001 266.9 to 
876.9 
 IbCh Lfm vs LgCh Lfm 25.88 0.3639 P > 0.05 -284.1 to 
335.8 
 *IbCh Lfm vs LgCh Mfm 403.4 5.42 P < 0.01 79.02 to 
727.7 
IbCh Mfm vs LgCh Lmkt -328.9 4.617 P < 0.05 -639.3 to -
18.47 
IbCh Mfm vs LgCh Mmkt -17.01 0.2412 P > 0.05 -324.2 to 
290.2 
*IbCh Mfm vs LgCh Lfm -563 7.861 P < 0.001 -875.2 to -
250.9 
IbCh Mfm vs LgCh Mfm -185.6 2.477 P > 0.05 -512.0 to 
140.9 
*LgCh Lmkt vs LgCh Mmkt 311.9 4.604 P < 0.05 16.66 to 
607.1 
LgCh Lmkt vs LgCh Lfm -234.1 3.397 P > 0.05 -534.5 to 
66.21 
 LgCh Lmkt vs LgCh Mfm 143.3 1.982 P > 0.05 -171.8 to 
458.5 
 *LgCh Mmkt vs LgCh Lfm -546 8.012 P < 0.001 -843.1 to -
249.0 
 LgCh Mmkt vs LgCh Mfm -168.6 2.354 P > 0.05 -480.6 to 
143.5 
 *LgCh Lfm vs LgCh Mfm 377.5 5.192 P < 0.01 60.63 to 
694.3 
Key: * significant diff. 
IbChLmkt = Ibadan chicken Liver (market); IbChMmkt = Ibadan chicken muscle (market); IbChLfm = Ibadan chicken Liver (farm); 
IbChMfm = Ibadan chicken muscle (farm); LgChLmkt = Lagos chicken Liver (market); LgChMmkt = Lagos chicken muscle (market); 
LgChLfm = Lagos chicken Liver (farm); LgChMfm = Lagos chicken muscle (farm) 
 
One-way analysis of variance (ANOVA) of oxytetracycline in chicken & beef 
  P value P<0.0001 
  P value summary *** 
  Are means signif. different? (P < 0.05) Yes 
  Number of groups 16 
  F 3.474 
  R squared 0.05236 
Tukey's Multiple Comparison Test of oxytetracycline residue in chicken-beef (Ibadan and Lagos) 
Tukey's Multiple Comparison Test Mean Diff. Q P value 95% CI of diff 
  IbCh Lmkt vs IbLD -775 3.21 P > 0.05 -1963 to 412.9 
  IbCh Lmkt vs IbMD 72.47 0.3001 P > 0.05 -1115 to 1260 
  IbCh Lmkt vs LgLD -397.9 1.641 P > 0.05 -1591 to 795.1 
  IbCh Lmkt vs LgMD 186.8 0.7737 P > 0.05 -1001 to 1375 
  IbCh Lmkt vs IbLW -831.5 3.444 P > 0.05 -2019 to 356.4 
  IbCh Lmkt vs IbMW -100.5 0.4163 P > 0.05 -1288 to 1087 
  IbCh Lmkt vs LgLW -887.7 3.676 P > 0.05 -2076 to 300.3 
  IbCh Lmkt vs LgMW 186.8 0.7737 P > 0.05 -1001 to 1375 
  IbCh Mmkt vs IbLD -1140 4.72 P > 0.05 -2328 to 48.27 
  IbCh Mmkt vs IbMD -292.2 1.21 P > 0.05 -1480 to 895.8 
  IbCh Mmkt vs LgLD -762.5 3.145 P > 0.05 -1955 to 430.5 
  IbCh Mmkt vs LgMD -177.8 0.7365 P > 0.05 -1366 to 1010 
  IbCh Mmkt vs IbLW -1196 4.954 P < 0.05 -2384 to -8.223 
  IbCh Mmkt vs IbMW -465.1 1.926 P > 0.05 -1653 to 722.8 
  IbCh Mmkt vs LgLW -1252 5.187 P < 0.05 -2440 to -64.36 
  IbCh Mmkt vs LgMW -177.8 0.7365 P > 0.05 -1366 to 1010 
  IbCh Mmkt vs LgLD -762.5 3.145 P > 0.05 -1955 to 430.5 
  IbCh Mmkt vs LgMD -177.8 0.7365 P > 0.05 -1366 to 1010 
  IbCh Mmkt vs IbLW -1196 4.954 P < 0.05 -2384 to -8.223 
  IbCh Mmkt vs IbMW -465.1 1.926 P > 0.05 -1653 to 722.8 
  IbCh Mmkt vs LgLW -1252 5.187 P < 0.05 -2440 to -64.36 
  IbCh Mmkt vs LgMW -177.8 0.7365 P > 0.05 -1366 to 1010 
  IbCh Lfm vs IbLD -318 1.317 P > 0.05 -1506 to 870.0 
  IbCh Lfm vs IbMD 529.6 2.193 P > 0.05 -658.4 to 1718 
  IbCh Lfm vs LgLD 59.2 0.2441 P > 0.05 -1134 to 1252 
  IbCh Lfm vs LgMD 643.9 2.667 P > 0.05 -544.1 to 1832 
  IbCh Lfm vs IbLW -374.5 1.551 P > 0.05 -1562 to 813.5 
  IbCh Lfm vs IbMW 356.6 1.477 P > 0.05 -831.4 to 1545 
  IbCh Lfm vs LgLW -430.6 1.783 P > 0.05 -1619 to 757.4 
  IbCh Lfm vs LgMW 643.9 2.667 P > 0.05 -544.1 to 1832 
  IbChMfm vs IbLD -1112 4.605 P > 0.05 -2300 to 76.09 
  IbChMfm vs IbMD -264.3 1.095 P > 0.05 -1452 to 923.6 
  IbChMfm vs LgLD -734.7 3.03 P > 0.05 -1928 to 458.3 
  IbChMfm vs LgMD -150 0.6213 P > 0.05 -1338 to 1038 
  IbChMfm vs IbLW -1168 4.839 P > 0.05 -2356 to 19.59 
  IbChMfm vs IbMW -437.3 1.811 P > 0.05 -1625 to 750.6 
  IbChMfm vs LgLW -1225 5.071 P < 0.05 -2412 to -36.55 
  IbChMfm vs LgMW -150 0.6213 P > 0.05 -1338 to 1038 
  LgCh Lmkt vs IbLD -908.5 3.763 P > 0.05 -2096 to 279.5 
  LgCh Lmkt vs IbMD -60.98 0.2525 P > 0.05 -1249 to 1127 
  LgCh Lmkt vs LgLD -531.3 2.191 P > 0.05 -1724 to 661.6 
  LgCh Lmkt vs LgMD 53.36 0.221 P > 0.05 -1135 to 1241 
  LgCh Lmkt vs IbLW -965 3.997 P > 0.05 -2153 to 223.0 
  LgCh Lmkt vs IbMW -234 0.969 P > 0.05 -1422 to 954.0 
  LgCh Lmkt vs LgLW -1021 4.229 P > 0.05 -2209 to 166.8 
  LgCh Lmkt vs LgMW 53.36 0.221 P > 0.05 -1135 to 1241 
  LgCh Mmkt vs LgCh Lfm -1095 4.535 P > 0.05 -2283 to 92.87 
  LgCh Mmkt vs LgCh Mfm -478.6 1.982 P > 0.05 -1667 to 709.4 
  LgCh Mmkt vs IbLD -1113 4.608 P > 0.05 -2301 to 75.39 
  LgCh Mmkt vs IbMD -265 1.098 P > 0.05 -1453 to 922.9 
  LgCh Mmkt vs LgLD -735.4 3.033 P > 0.05 -1928 to 457.6 
  LgCh Mmkt vs LgMD -150.7 0.6242 P > 0.05 -1339 to 1037 
  LgCh Mmkt vs IbLW -1169 4.842 P > 0.05 -2357 to 18.89 
  LgCh Mmkt vs IbMW -438 1.814 P > 0.05 -1626 to 749.9 
  LgCh Mmkt vs LgLW -1225 5.074 P < 0.05 -2413 to -37.25 
  LgCh Mmkt vs LgMW -150.7 0.6242 P > 0.05 -1339 to 1037 
  LgCh Lfm vs LgCh Mfm 616.5 2.553 P > 0.05 -571.5 to 1804 
  LgCh Lfm vs IbLD -17.48 0.07238 P > 0.05 -1205 to 1170 
  LgCh Lfm vs IbMD 830 3.438 P > 0.05 -357.9 to 2018 
  LgCh Lfm vs LgLD 359.7 1.483 P > 0.05 -833.3 to 1553 
  LgCh Lfm vs LgMD 944.4 3.911 P > 0.05 -243.6 to 2132 
  LgCh Lfm vs IbLW -73.97 0.3064 P > 0.05 -1262 to 1114 
  LgCh Lfm vs IbMW 657.1 2.721 P > 0.05 -530.9 to 1845 
  LgCh Lfm vs LgLW -130.1 0.5389 P > 0.05 -1318 to 1058 
  LgCh Lfm vs LgMW 944.4 3.911 P > 0.05 -243.6 to 2132 
  LgCh Mfm vs IbLD -634 2.626 P > 0.05 -1822 to 554.0 
  LgCh Mfm vs IbMD 213.5 0.8844 P > 0.05 -974.4 to 1401 
  LgCh Mfm vs LgLD -256.8 1.059 P > 0.05 -1450 to 936.2 
  LgCh Mfm vs LgMD 327.9 1.358 P > 0.05 -860.1 to 1516 
  LgCh Mfm vs IbLW -690.5 2.86 P > 0.05 -1878 to 497.5 
  LgCh Mfm vs IbMW 40.55 0.168 P > 0.05 -1147 to 1229 
  LgCh Mfm vs LgLW -746.6 3.092 P > 0.05 -1935 to 441.3 
  LgCh Mfm vs LgMW 327.9 1.358 P > 0.05 -860.1 to 1516