Antibacterial Activity of Metabolites of Endophytic Bacillus subtilis Isolated From Selected Ethiopian Medicinal Plants

Abstract

Antimicrobial resistance remains a global concern, and there has been sustained exploration of natural products with therapeutic effects. Endophytes are among the potential microorganisms considered as the treasure chest for bioactive secondary metabolites with therapeutic effects. The current study was aimed at evaluating the antibacterial activity of endophytic Bacillus subtilis isolated from selected Ethiopian medicinal plants (Kalanchoe petitiana, Artemisia abyssinica, Rumex abyssinicus, and Clematis longicauda). Collection of the plant samples, endophyte isolation, metabolite production, and antimicrobial activities were conducted following standard protocols. The isolates were further identified at the molecular level using 16S rRNA gene sequence. The endophytic crude extract demonstrated inhibition zones (millimeter) ranging from 6.00 ± 0.00 against Pseudomonas aeruginosa to 22.00 ± 0.71 against Salmonella Typhimurium. In general, S. Typhimurium was the most sensitive, followed by Escherichia coli, but P. aeruginosa was the least sensitive to the extracts. The extract from isolate En6 produced the largest inhibition zone against Staphylococcus aureus, but the extract from Ch1 produced pronounced inhibition against E. coli, S. Typhimurium, and P. aeruginosa. The lowest minimum inhibitory concentration and minimum bactericidal concentration values ((Formula presented.) in milligram/milliliter) of 0.025 ± 0.01 and 0.98 ± 0.01, respectively, were recorded against S. Typhimurium by the extract from isolate Ch1. Molecular characterization confirmed that the isolates were members of B. subtilis. This is the first report of the isolation of endophytes with antibacterial activities from the Ethiopian medicinal plants. The strong inhibitory activity of the metabolites against the selected test bacteria shows the potential of the endophytic metabolites for use as antibacterial agents with further studies.