Selection of indigenous Lactobacillus paracasei CD4 and Lactobacillus gastricus BTM 7 as probiotic: assessment of traits combined with principal component analysis

Aims: The population of the Himalayan region is known to consume a variety of fermented and nonfermented foods and as a result they have been benefited in terms of overall health, because of the associated beneficial microbes. Therefore, the focus of the present study was to identify new strains of lactic acid bacteria (LAB) from dairy products such as milk (cow, goat, buffalo) and fermented products (curd and buttermilk) with properties suitable for use as probiotic cultures.

Methods and results: A total of 75 isolates tentatively identified as LAB from 100 samples were initially screened for production of β-haemolysin as indicators of virulence which resulted in 38 isolates with no haemolytic activity. Further subtractive screening based on resistance to gastrointestinal tract barriers (acid and bile salts) resulted in the selection of the eight most promising strains. All these eight strains were resistant to pH 2·0, 1% bile concentration and pancreatin (1 mg l^-1 ). Among the eight isolates, three isolates were identified as Brevibacillus thermoruber and the others as Brevibacillus aydinogluensis, Lactobacillus gastricus, L. paracasei, Enterococcus sp. Weisella confusa based on 16S rDNA region. Among these isolates, L. paracasei CD4 and L. gastricus BTM7 indicated maximum tolerance to simulated gastric environment. Both the isolates possessed highest score for cell surface hydrophobicity, cell autoaggregation, adherence to Caco-2 cell lines and antimicrobial activity against clinical isolates of Escherichia coli and Shigella sp. comparable to standard strain of Lactobacillus rhamnosus GG. Further principal component analysis and clustering analysis based on Euclidean Similarity index of probiotic characters revealed that L. paracasei strain CD4 and L. gastricus strain BTM7 were placed closest to reference strain L. rhamnosus GG and were therefore identified as most promising probiotic candidate cultures.

Conclusions: These characteristics suggest that these strains could be excellent candidates for probiotics.

Significance and impact of the study: Milk-based products serve as reservoir for bacterial species with probiotic attributes.