Antimicrobial activity of crude extracts and alkaloidal fractions of Argemone mexicana Linn

Abstract

Emergence of multi-drug resistant pathogens lias necessitated the need for continuous research to discover and develop new and more effective antimicrobial drugs. Medicinal plants have always been a potential source of antimicrobial drugs and varieties of lead compounds. Argemone mexicana, a tropical shrub traditionally used to treat eye infections, inflammation and infertility was investigated for antibacterial activity. Crude chloroform and methanol extracts of leaves and stems, as well as fractions and crystals from chromatographic column were screened for in-vitro antibacterial activity against Staphylococcus aureus (NCTC 6571), Bacillus subtilis (ATCC 6633) Escherichia coli (NCTC. 9001) and-Pseudomonas aeruginosa (NCTC 6570) using agar-cup diffusion method. Phytochemical screening for secondary metabolites revealed the presence p f alkaloids (opium and indole types) and tannins. The crude extracts showed good activity at 100mg/ml against the bacterial strains tested while at 10mg/ml only E. coli and B. subtilis were susceptible. JTen fractions were isolated from column chromatography (nine of which were alkaloidal in nature), and they all showed varying but significant degree of activity on most of the tested organisms at 100pg/ml. The needle-like crystals recovered from methanol extract showed weak antibacterial activity on some of the test organisms. The study has shown that A. mexicana leaves and stem bark has antibacterial activity which justified the use of this plant in traditional medicine as anti-infective agent. Further, the fact that most fractions showed antibacterial activity is an indication that Argemone mexicana leaf and bark has many antibacterial constituents that are mainly alkaloidal.