Isolation of bacteriocin nisin producing Lactococcus lactis from dairy ...

J. Acad. Indus. Res. Vol. 1(10) March 2013 630This indicated that crude bacteriocin produced byL. lactis was heat stable at 100C. The hypothesis of thisstudy was to demonstrate that the optimum temperaturefor cell growth should be the optimum for bacteriocinproduction as well. Therefore, the bacteriocin productionwas conducted at 37C. E. coli was least sensitive toinhibitory substance produced by LAB as compared toother indicator strain. The resistance of gram-negativebacteria is attributed to the particular nature of their cellenvelop, the mechanism of action described forbacteriocin. This could be due to fact that these isolatesare nisin producers (Soomro et al., 2002) and theprimary target of nisin antimicrobial action is the cellmembranes. Nisin has a inhibitory effect against a widevariety of gram-positive food borne pathogens andspoilage microorganisms (Rodriguez, 1996). In thisstudy, wider inhibition zone were observed by theLactococcus on the test strains. Similarly, Kellyet al. (1996) and Hernandez et al. (2005) reported thatseveral Lactococci produced nisin like activity andshowed a broad inhibitory spectrum against the indicatorstrains tested.ConclusionThe culture filtrates from L. lactis isolated from dairyproducts exhibited antimicrobial activity against threeindicator test strains. The test isolate was grown in MRSmedium under optimized conditions. Bacteriocin activityof the test isolate was determined by agar well diffusionassay against Escherichia coli, Staphylococcus aureusand Bacillus sp. The optimum temperature of L. lactis inMRS medium was 37C. Highest viable cell count ofL. lactis at 37C reached about 8.54 log cfu/mL in 8 h.Bacteriocin nisin production was maximized whenL. lactis was grown in controlled pH fermentation mediumof 6.5. Bacteriocin supernatant of L. lactis was heatstable, as the inhibition activity remained constant afterheating at 80C for 20 min. 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Biochem. 67: 1616-1619.©Youth Education and Research Trust (YERT) Nagalakshmi et al., 2013