In vitro antibacterial activity of Bersama abyssinica Fresen crude extract against representative Gram-positive and Gram-negative bacterial isolates

Background: Bersama abyssinica Fresen is a plant that is used in folk medicine for the treatment of mastitis and other infectious diseases. ObiectiveThe antibacterial activity of methanol crude extract of plant was evaluated against three common bacterial pathogens, including Gram positive (Staphylococcus aureus) and Gram negative (Escherichia coli and Pseudomonas aeruginosa). Methods: The antibacterial activities and minimum inhibitory concentration of B. abyssinica crude extracts were evaluated using agar-well diffusion and broth dilution methods according to the National Committee for Clinical Laboratory Standards (NCCLS). Results: A significant difference in the antibacterial activity of crude extracts was observed among different levels of concentration against tested isolates. A higher mean inhibition zone diameter was recorded in E. coli (29.2 +/- 1.5 mm), followed by S. aureus (27.8 +/- 1.1 mm) and P. aeruginosa (18.0 +/- 0.7 mm) at a concentration of 100 mg/mL. The antibacterial activity of crude plant extract at 100 mg/mL was comparable with that of a standard antibiotic (27.6 +/- 2.6) against S. aureus and E. coli isolates. The findings indicated that bacterial growth inhibition increased as the concentration of the crude extracts increased. E. coli and S. aureus isolates showed significantly higher susceptibilities to crude extracts than P. aeruginosa at all concentrations. The minimum inhibitory concentrations of extracts against S. aureus, E. coli and P. aeruginosa isolates were 0.78 mg/mL, 1.56 mg/mL and 1.56 mg/mL, respectively. Conclusions: All tested pathogenic bacterial species were susceptible to plant leaf extract and broad-spectrum activity against Gram-positive and Gram-negative bacteria. The study recommends further fractionation of the B. abyssinica plant that contributes to its antibacterial activity and understands the mode of action of this plant against bacteria and other microbes.