Isolation and molecular analysis of bacilli producing bacteriocins with broad-spectrum antimicrobial potential from fermented milk and kefir

This study aims to evaluate antimicrobial properties of bacteriocin-like inhibitory substances produced by the strains of Bacilli isolated from a probiotic drink called kefir. Kefir contains gut-friendly bacteria and is a popular fermented drink worldwide. Bacillus subtilis and Bacillus licheniformis strains isolated from goat milk and milk kefir were investigated for bacteriocin production. Crude bacteriocin present in cell-free supernatant obtained after fermentation of isolated culture in MRS media exhibits prominent antibacterial effects against a wide range of Gram-positive and Gram-negative bacteria. The size of the protein was found to be approximately 16kD when analyzed by SDS-polyacrylamide gel electrophoresis. Effects of various physical and chemical parameters were studied, and shown in terms of zone of inhibition using a wide range of indicator strains such as Listeria monocytogenes MTCC657, Staphylococcus aureus MTCC1430, Enterococcus faecalis MTCC 3159, Escherichia coli ATCC 25922, and L. lactis subsp. cremoris MTCC 1484. Maximum inhibitory activity of bacteriocin produced by milk kefir was achieved in 24 h of incubation at an initial neutral pH and temperature of 37°C. A considerable change in bacterial growth and activity of bacteriocin was observed at values considerably above or below the optimum.