Abstract

Lactic acid bacteria (LAB) commonly used in food, as starter cultures are known to produce antimicrobial substances such as bacteriocins and have great potential as food bio-preservatives. Yogurt is a probiotic dairy product having Lactobacillus bulgaricus as natural source for fermentation. The aim of this study was to determine the antimicrobial activity of bacteriocin, produced by Lactobacillus bulgaricus isolated from yogurt and tested against pathogenic organisms. The identification of the culture was based on characteristics of the strains of Lactobacillus spp. on the basis of microscopy (morphology), Gram straining, growth at 37 and 45°C, fermentation of different carbohydrate sources and growth in MRS broth. On the basis of all of the identification tests, one strain isolated from the yogurt was identified as L. bulgaricus. Culture supernatants were obtained from the sixty out of hundred isolates of Lactobacillus spp. exhibited varying degrees of inhibitory activity against strains of  Bacillus subtilis, ATCC #6633, Escherichia coli, ATCC, #10536, Salmonella typhi, ATCC# 19430,Staphylococcus aureus, ATCC #6538, Vibrio cholerae, ATCC #25870. Specifically, Vibrio cholerae was found most sensitive to bacteriocin, exhibiting maximum zone of inhibition 18.3 mm.

Key words: Lactic acid bacteria (LAB), Lactobacillus bulgaricus, bacteriocin, yogurt, antimicrobial activity, Pakistan.