ENHANCEMENT OF ANTIBACTERIAL ACTIVITY OF AMOXICILLIN BY SOME GHANAIAN MEDICINAL PLANT EXTRACTS

As part of our ongoing study to screen local herbs for their possible usefulness as anti-infectives, we assessed extracts from 16 medicinal plants for their antibacterial properties and their influence on the activity of amoxicillin. The minimum inhibitory concentrations (MIC) of amoxicillin against Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli and Salmonella typhi were determined alone and in the presence of sub-inhibitory concentrations of the extracts by the Kirby–Bauer agar diffusion method of antibacterial assay. Eleven out of 18 extracts exhibited antibacterial activity with MIC values below 20 mg/ml against at least one of the test bacteria employed. Amoxicillin activity against Staph. aureus was significantly (p<0.05) enhanced by the presence of sub-inhibitory concentrations of 5 extracts (Mallotus oppositifolius, Bidens pilosa, Morinda lucida, Croton membranaceus and Jatropha curcas). B. subtilis also became significantly susceptible to amoxicillin in the presence of 10 μg/ml extracts of B. pilosa, Hibiscus sabdariffa, M. oppositifolius, Momordica charantia, Anoclesta nobilis, Cryptolepis sanguinolenta and Moringa oleifera. Spathodia campanulata, M. lucida, M. oleifera and J. curcas leaf extracts also significantly reduced the MIC of amoxicillin against E. coli while S. typhi susceptibility was enhanced by the presence of A. nobilis, M. charantia and J. curcas extracts. We hereby report that sub-inhibitory concentrations of some plant extracts can enhance amoxicillin activity and these plants may provide lead compounds that may serve as cheap alternative adjuvants to clavulanic acid in amoxicillin formulations for the treatment of resistant opportunistic bacterial infections usually encountered among HIV/AIDS patients.