Screening and isolation of Bacillus strains with antagonistic activity against pathogens from Thai traditional fermented soybean food

This study aimed to isolate Bacillus strains from Thai traditional fermented soybean food (Thua nao) with antagonistic activity against pathogens. The isolates were evaluated for antagonistic activity against Salmonella enteritidis TISTR1469, Escherichia coli TISTR117, Bacillus cereus TISTR747, Staphylococcus aureus TISTR746, and Pseudomonas aeruginosa TISTR1287 by the colony streak plate method. Among 223 strains, 11 strains showed zones of inhibition against at least one of the pathogens, while only one strain, LK 1.13, exhibited high inhibition zone against all selected indicator pathogens. Based on 16s rRNA gene sequencing, strain LK1.13 was identified as Bacillus pumilus. Interestingly, B. pumilus strain LK 1.13 displayed significant antimicrobial activities against all studied pathogens, comparable to four different types of antibiotics: chloramphenicol, ampicillin, kanamycin, and tetracycline by the agar-well diffusion method. Therefore, this broad-spectrum antimicrobial activity of B. pumilus strain LK1.13 signals its application prospects in the medical and pharmaceutical industries.