Evaluation of the Antimicrobial Activity of Leaf Extract of Ageratum conyzoides against Multidrug-resistant Gram-negative Bacterial Isolates from Infected Surgical Wounds

Abstract

Multidrug-resistant (MDR) Gram-negative bacteria are a major cause of post-surgical wound infections and present a growing challenge to effective treatment. The search for alternative therapies, including medicinal plants, has therefore become essential. This study investigated the antimicrobial effect of leaf extract of Ageratum conyzoides against MDR Gram-negative bacterial isolates obtained from infected surgical wounds. Eleven bacterial isolates were characterized using biochemical and sugar fermentation tests to determine their physiological traits, while antibiotic sensitivity testing was performed on commonly used drugs with a view to identify resistance patterns and select MDR strains. The methanolic leaf extract of Ageratum conyzoides was evaluated for antimicrobial activity against MDR isolates using the agar well diffusion method, and its minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) was assessed. The isolates were predominantly Enterobacteriaceae (Escherichia sp., Klebsiella sp. Pseudomonas sp. and so on) with diverse metabolic profiles. Antibiotic sensitivity testing revealed widespread resistance to ampicillin, penicillin, tetracycline, and streptomycin, while partial susceptibility remained to levofloxacin, ofloxacin, and gentamicin. The selected MDR strains (Klebsiella sp., Pseudomonas sp., and Proteus sp.)  exhibited resistance to nearly all tested antibiotics. A. conyzoides leaf extract showed no zones of inhibition and no measurable MIC or MBC values against the MDR strains but, demonstrated significant antimicrobial activity against the susceptible (non-clinical) control strains used; Escherichia coli (1.44 mm), Pseudomonas aeruginosa (1.3mm), and Klebsiella pneumonia (0.9mm).   These findings emphasize the urgent need for prudent antibiotic use, continuous monitoring of resistance, and further exploration of plant-derived compounds through improved extraction methods or synergistic applications with conventional antibiotics.