Antagonistic effects of Bacillus species against bacterial multi-drug resistant (MDR) food-borne pathogens and aflatoxigenic fungi

This study was designed to investigate the antagonistic pattern of Bacillus species against MDR bacterial food-borne pathogens and aflatoxigenic fungi and evaluate their technological properties. Morphological and biochemical characterizations were done using standard methods. Production of cell-free metabolites, agar well diffusion, optimization of Bacillus growth rates, and enzymatic assays were also carried out using standard techniques, while aflatoxin quantification and qualification were done using high-performance thin-layer chromatography (HP-TLC). Results revealed that B. subtilis OKOI7.12ia had the highest inhibitory activity against S. enteritidis ATCC 13875 (27mm), while B. paralicheniformis had the least inhibitory activity against A. niger (7mm). B. subtilis OKOI7.12ia also had the highest growth rate at 30°C, followed by B. subtilis IPOI3.12ia and B. paralicheniformis OKAO4.12ia. However, there was no significant difference in the growth rates of B. subtilis IPOI3.12ia at 30°C and 40°C (p < 0.05). Furthermore, B. subtilis OKOI7.12ia and B. subtilis IPOI3.12ia had the highest growth rate at pH 8, while a lower growth rate was observed at pH 6 (p < 0.05) in all five Bacillus sp. In addition, B. subtilis OKOI7.12ia and B. subtilis IPOI5.10ia had the highest growth rates using glucose and galactose as carbon sources, respectively. Growth in nitrogen sources showed that B. subtilis OKOI7.12ia had the highest growth rate, while B. subtilis IPOI5.10ia and B. subtilis OGOA10.7ii growths were not significantly different at p < 0.05. More so, B. subtilis IPOI3.12i had the least growth in peptone. In addition, B. subtilis OKOI7.12ia also produced the highest amounts of protease, amylase, and lipase enzymes, while B. subtilis IPOI3.12ia produced the least. Therefore, from the results obtained in this study, it can be concluded that B. subtilis OKOI7.12ia can be employed as a potential starter culture for producing microbiologically safe foods.