Isolation and characterization of bacteriocin-like inhibitory substances producing lactic acid bacteria from indigenous food samples.

Background: Lactic acid bacteria (LAB) are generally found in nutrient-rich environments such as milk, dairy products, meat, vegetables, and fruits. The functions of LAB depend upon the sufficient number of bacteria being available in the intestines, and the actions of these bacteria are generally species and strain-specific. The challenges encountered in identifying and classifying lactic acid bacteria have complicated the research process. Despite encountered challenges, various benefits of lactic acid bacteria have been identified. The current study aimed to isolate and characterize indigenous LAB bacteriocins producers from local food sources using morphological, biochemical, and molecular methods. Methodology: One thousand indigenous LAB were isolated and screened from local fresh and fermented foods in Karachi's retail markets for three years. 46 LAB isolates exhibited inhibitory activity against other LAB and non-LAB gram-positive bacteria in broth medium. Three of forty-six isolates were selected for further study of the nature and production of the inhibitory substance based on production in broth, bacteriocin nature of the substance, and relatively wide antibacterial spectrum. Results: The three indigenous LAB producers were identified as Lactococci based on microscopy, catalase, biochemical and molecular characterization. Bacteriocin of the isolate C130 was heat tolerant at 100°C and produced during the late logarithmic phase of growth. There is still a need for investigation to identify the role of LAB, which might help prevent certain chronic illnesses and infections. Most beneficial impacts are known in constipation, hypocholesterolemic effects, urogenital infections, and colon cancer.   Conclusion: L. lactis C130 was found to be a thermostable bacteriocin producer with a fair antibacterial spectrum against various food spoilage.