Antimicrobial Activity and Characterization of Lactobacillus reuteri Isolated From Human Milk

Breast milk is the primary food for an infant. Chief ingredients of breast milk include lactobacillus strains. Lactobacillus strains isolated from breast milk were investigated for their antimicrobial activity against pathogenic microorganisms. The antibacterial activity is attributed to bacteriocin secreted by Lactobacillus. Bacteriocin present in cell free supernatants of Lactobacillus reuteri exhibited inhibitory activity against microorganisms such as Escherichia coli, Shigella dysentriae, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhi, Proteus spp. and Vibrio cholera by agar well diffusion method. Optimization of bacteriocin production and characterization of extra cellular bacteriocin were studied. The bacteriocin produced by Lactobacillus reuteri was stable at 600C for 10 minutes, but inactivated by heating at 80°C for 10 minutes. It was stable at pH 4.0 to 7.0 but sensitive to pH 9.0. 1% and 2% sodium chloride enhanced the production of bacteriocin from 25% to 75% in MRS broth. Molecular weight of bacteriocin purified by ammonium sulphate precipitation method was 2.5 kDa. Thus, bacteriocin of Lactobacillus reuteri strains isolated from human milk exhibited antibacterial activity against common clinical pathogens. It also exhibited properties of a good probiotic.