Abstract

Bacteriocins are natural antimicrobial peptides with potential applications in human health care and exhibit a bactericidal mode of action against different microorganisms. The present study was carried out to observe lactic acid bacteria prevalence in milk and to determine the antimicrobial activity of Lactococcus lactis bacteriocin against Salmonella typhi.  Isolation and characterization of lactic acid bacteria was carried out on the basis of morphological, physiological and biochemical tests. Cell free extracts of bacteriocins were prepared by the ammonium sulphate precipitation. Antimicrobial activity was performed by Disc Diffusion method by using different organic solvents. It was observed that the genusLactococcus was common (75%) in different milk samples. Antimicrobial activity of bacteriocin was increased in different solvents. Antimicrobial activity was maximum (17.0 ± 0.7 mm) at 90:10 bacteriocin and ethanol ratio, on the other hand it was minimum (8.5 ± 0.5 mm) at 25:75 bacteriocin and ethanol ratio at pH 6.0. It was stable at higher temperature (100°C for 60 min). Sensitivity test confirmed that bacteriocin lost its activity after treating with proteinase K (0.1 mg/ml).

Key words: Bacteriocin, lactic acid bacteria, Lactococcus lactis, Salmonella

Abbreviation

CFS, Cell free supernatant; CDC, centre for disease control and prevention; LAB, lactic acid bacteria; WHO, World Health Organization; MRS, de Man Rogosa and Sharpe