Isolation of bacteriocin nisin producing Lactococcus lactis from dairy products

Most inhibitory substances produced by lactic acid bacteria are safe and effective natural inhibitors of pathogenic and food spoilage bacteria in various foods. In this study, bacteriocin nisin producing Lactococcus lactis was isolated from fermented milk and cheese. The test isolate was grown in MRS medium under optimized conditions. Bacteriocin activity of the test isolate was determined by agar well diffusion assay against Escherichia coli, Staphylococcus aureus and Bacillus sp. The optimum temperature of L. lactis in MRS medium was 37C and the highest viable cell count of L. lactis at 37C reached about 8.54 log cfu/mL in 8 h and 8.10 log cfu/mL in 14 h. Bacteriocin nisin production was maximized when L. lactis was grown in controlled pH fermentation medium of 6.5. Bacteriocin supernatant (CBS) of L. lactis was heat stable, as the inhibition activity remained constant after heating at 80C for 20 min. The results revealed that E. coli was least sensitive to crude bacteriocin supernatant of L. lactis as compared to other indicator strains.