Multidrug Resistant Strains Inhibition by Bacillus Species from the Gut of Oreochomis niloticus and Pomacea canaliculata

Abstract

Antibiotic resistance is widespread in clinical settings, indicating a serious problem with infectious disease treatment. Novel strategies such as using natural products derived from microbes are being explored, generating increased research interest to address this issue. Here, the antimicrobial property of gut-associated Bacillus species against multidrug-resistant (MDR) strains; methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli producing extended-spectrum beta-lactamase (EsβL E. coli), and Pseudomonas aeruginosa producing metallo beta-lactamase (MβL P.aeruginosa) was evaluated using a cross-streak method and agar diffusion assay. The Bacillus isolates inhibited MRSA and ESβL E. coli with an average zone of inhibition of 9.57 ± 33.40 mm and 5.07 ± 32.69 mm, respectively, in the cross-streak method. The cell-free supernatant (CFS) of ten Bacillus species demonstrated anti-MRSA activity but was ineffective against ESβL E. coli and MβL P. aeruginosa. The relative enzyme activities of ten Bacillus isolates were determined in vitro, and amylase, caseinase, cellulase, lipase, and gelatinase production were confirmed. Isolates were identified as Bacillus siamensis, Bacillus velezensis, and Bacillus subtilis through biochemical tests and 16s rRNA sequence analysis. Minimum inhibitory concentrations (MICs) of the CFSs against MRSA range is between 12.5 and 25%. Bacillus species isolated from fish and snail guts exhibited antibacterial activity against MRSA. Therefore, it is imperative to confirm the presence of anti-MRSA active compounds in Bacillus CFS and characterize them further to determine their suitability for antimicrobial drug development.