Bacteriocin production by Enterococcus sp isolated from rat intestine

Lactic acid bacteria are widely known for their inherent ability to produce antimicrobial substances such as bacteriocins, which are ribosomally synthesized low-molecular weight proteins. The bacteriocins have great potential to antagonize food borne pathogens and spoilage microorganisms and they are being used as food biopreservatives. Attempts have been made to isolate bacteriocin producing lactic acid bacteria from rat intestine. Three bacterial strains i.e. DFR8, DFR15 and DFR25 were found to produce substantial amount of bacteriocins. All the 3 bacterial isolates were found to be cocci, homo-fermentative and catalase negative. Growth of these isolates at different temperatures, pH and in the presence of NaCl was studied. Optimum growth was found to be at 37°C and the strains were able to grow at high pH between 8.6 and 9.2, in the presence of 4% NaCl but not in media containing 6% and 10% of NaCl. Carbohydrate utilization and biochemical tests were performed for their identification. Based on morphological, physiological and biochemical characteristics DFR8 and DFR25 were identified as Enterococcus faecium and DFR15 as Enterococcus faecalis. The bacteriocins produced by these isolates showed broad inhibitory spectrum against various food borne pathogens and some standard lactic acid bacteria. Optimization of medium ingredients to improve the growth and bacteriocin production was accomplished. Partially purified bacteriocins were analyzed by tris-tricine SDS-PAGE indicating the molecular mass of the protein between 3.0 and 3.5 kDa.