Lactic acid bacteria (135) were isolated and screened for bacteriocin production by agar overlay method. Among them, Lactobacillus paracasei subsp. tolerans isolated from locally available cheese showed maximum zone of inhibition (24-26 mm) against food borne (Listeria monocytogenes, Staphylococcus aureus) and human pathogens (Escherichia coli, Salmonella typhi). Bacteriocin was found to be proteinaceous in nature, heat stable (1210 C for 15 min) and active over a wide pH range of 4.0-8.0. It showed stability (60 %) for 30 days at room temperature (30- 320C). Addition of surfactants (EDTA, SDS, hexadecyl trimethylamonium bromide) up to 1% to crude bacteriocin showed increase in antibacterial activity where as metal ions (calcium chloride, zinc sulphate and mercuric chloride) in low concentration (0.5-1 mgl-1) decreased the activity. The bacteriocin was purified to its homogeneity by ammonium sulfate precipitation, gel filtration chromatography and HPLC. Molecular weight of bacteriocin was found to be 8.6 and 8.3 KDa by SDS PAGE and LC/MS respectively. Maximum Bacteriocin production was obtained at 35ºC, pH 7.0, NaCl (0.2%) after 28h of incubation. Addition of L-Ascorbic acid increased bactreiocin production. Our present study demonstrates the possibility of using L. paracasei subsp. tolerans as a biopreservative in dairy industry
