Isolation and characterization of lactic acid bacteria and their inhibitory/safety potential in traditionally fermented milk, mursik in Kenya

Abstract

Commercial fermented milks have health benefit potential attributed to pure probiotics used as starter culture. Lactic acid bacteria (LABs) are the probiotics used. LABs promote stabilization of the gastrointestinal microecology of humans by producing secondary metabolites like lactic, acetic and propionic acid, hydrogen peroxide and bacteriocins (bactericidal proteins). These metabolites are health benefiting. Mursik, an indigenous fermented milk product is consumed by many Kenyan communities, specifically the Kalenjin. The fermentation of mursik is not based on pure cultures, instead it is spontaneous. Whether the types and concentrations of the probiotics in this traditionally fermented milk have the same probiotic potential as those of commercial fermented milk is not documented. This study aimed at isolating mursik probiotics and determining their probiotic potential. Mursik was obtained from informal women groups and individuals involved in small scale production and marketing in Bomet County, Kenya. Two types of mursik are made in this county; smoked and non-smoked. A total of forty one (41) mursik samples were collected and analysed. Type and concentration of the probiotics was determined by pour plate method. The inhibitory/safety potential was determined by acid and bile tolerance, as well using disc diffusion method against Salmonella enterica ATCC 13076, Escherichia coli ATCC 25922 and Staphylococcus aureus isolate which were used as standard strains of public health concern. Data was analyzed using analysis of variance (ANOVA) and chi-square tests at α = 0.05. 78 % of the samples had a microbial load of ≥ 107 cfu/ml. LABs formed 80 % of the microbial load in mursik. The remaining 20 % consisted of coliforms and spore forming bacteria. The main probiotics isolated from mursik were, Lactobacillus plantarum, Lactobacillus fermentum, Lactobacillus brevis and Lactobacillus casei. The metabolites produced by the isolated probiotics in broth demonstrated significant (P<0.05) antibacterial effect against the standard strains of public health concern used. The results obtained from this study confirm that probiotics exist in mursik, a traditionally fermented milk product and that these probiotics have significant potential against enteric and environmental pathogens that are of public health concern