In-vitro evaluation of the antimicrobial activity of extracts of Bridelia micrantha on selected bacterial pathogens

Medicinal plants have been age long remedies for human diseases because they contain components of therapeutic value. In this study, six solvent extracts [dichloromethane, ethyl acetate, acetone, ethanol, methanol (100%), and 40% methanol hydroxide] of the stem bark of Bridelia micrantha and ciprofloxacin were investigated for antimicrobial activity by the agar-well diffusion method against strains of Staphylococcus aureus NCTC 6571, Shigella sonnei ATCC 29930, Salmonella typhimurium ATCC 13311, Helicobacter pylori ATCC 43526, and Helicobacter pylori 252c. The most active extracts were assayed for MIC50 using the 96-well microdilution technique and one way ANOVA test was used to determine if there was any statistically significant difference in the MIC50 of the most active extracts and the control antibiotic (ciprofloxacin). Results obtained indicated that methanol was quantitatively the best solvent for extraction, while ethyl acetate was the least. Zone diameters of inhibition ranged from 0 to 28 mm for the six extracts and 29 to 38 mm for ciprofloxacin. Ethyl acetate and acetone extracts were the most active of all the extracts exhibiting a broad spectrum activity. However, Gram-positive bacteria were more sensitive compared to Gram-negative bacteria. The MIC50 value ranged from 0.078 to 1.25 mg/ml and 0.078 to 0.625 mg/ml for the acetone and ethyl acetate extracts respectively, with no statistically significant difference in potency (p value = 0.187) when compared to ciprofloxacin. Our findings demonstrate the in-vitro antibacterial activity of the crude extracts of B. micrantha, and therefore provide preliminary scientific evidence to justify the use of the plant in traditional medicine.