Probiotic potential of bacteriocin-producing Enterococcus hirae strain LD3 isolated from dosa batter

Enterococcus hirae LD3 was isolated from dosa batter and identified by biochemical and molecular techniques such as carbohydrate fermentation pattern and 16S rDNA amplification and sequencing. Strain LD3 demonstrated probiotic properties such as cell surface hydrophobicity, simulated gastric juice, bile salt and acid tolerance, and antibiotic susceptibility. The optimum growth of strain LD3 and bacteriocin production was observed at 37 degrees C, pH 7.0. Bacteriocin was produced during mid-log phase and found to be thermo-stable, demonstrated activity at an acidic pH range, and was stable in different organic solvents, surfactants, and detergents tested. The antimicrobial activity was not affected by amylase and lipase, but reduced after treatment with pepsin, trypsin, proteinase K, and papain suggesting a proteinaceous nature. Crude bacteriocin preparation inhibited a broad range of target bacteria belonging to both Gram-positive and Gram-negative groups, including Micrococcus luteus, Listeria monocytogenes, Salmonella typhi, Staphylococcus aureus, Shigella flexneri, Pseudomonas fluorescens, P. aeruginosa, Vibrio sp., and Escherichia coli O157:H7. Partially purified enterocin LD3 revealed a smear protein band with molecular weight between 3 and 7 kDa which showed a clear zone of inhibition after bioassay. Since strain LD3 has been isolated from a food source, it would be safe for human consumption in probiotic products or clinical applications.