Isolation and molecular identification of soil bacteria exhibiting a broad-spectrum of antibacterial activity against multi-drug resistant strains

Due to the increase in drug-resistant in pathogens, the search for new antibiotics from an unexplored natural environment is gaining momentum to combat Multidrug-resistant (MDR) bacteria. The genus bacillus has been found as a prolific source of antibacterial metabolites synthesis. The current study was intended to isolate antibacterial metabolites producing Bacillus spp. From the unexplored region of Pakistan. Initially, 49 Bacillus spp. Were isolated from 9 soil samples and evaluated for antibacterial activity against a set of American Type Culture Collection (ATCC) and MDR clinical bacterial strains. The isolate MK-12.1 antagonized the growth of ATCC, as well as MDR pathogenic bacterial strains, was selected for further study. The antibacterial metabolites were characterized and confirmed to be protein in nature, showed no hemolysis on human blood agarand molecular weight was >20 kDa. The antibacterial metabolite producing bacterial isolate was identified as Bacillus safensis strain MK-12.1 on the basis 16S rRNA gene sequencing analysis supported with biochemical testing. Various culturing parameters such as temperature, pH, incubation time and growth medium were optimized for growth and antibacterial metabolites synthesis. The optimum antibacterial activity and biomass was achieved at pH 8, 30 ⁰C after 48 hours in the shaking incubator when cultured in modified OPT medium. The present study revealed that soil of Kohat, Pakistan is rich in terms of antibacterial metabolites producing bacteria and could be a good source for antibacterial which leads to fight against MDR bacteria in the future.