CONICET | Buscador de Institutos y Recursos Humanos

Non-starter lactic acid bacteria isolated from Argentinean cheeses were identified and characterized by focusing on their resistance to biological barriers and other physiological features of potential interest for the search of future probiotic organisms. Lactobacilli were enumerated and isolated from semi-hard and soft cheeses made with multistrain Streptococcus thermophilus starters. Lactobacilli counts in one week-old cheeses were between 105 107 CFU/g then reached 107 CFU/g in all one month samples, while strepctococci were always above 109 CFU/g. A final number of 22 lactobacilli isolates were retained, identified and characterized by in vitro tests. Species identity was determined by carbohydrate metabolism and species-specific PCR assays. Genetic diversity was explored by RAPD-PCR analysis. The strains were assigned to the species Lactobacillus casei, L. plantarum, L. rhamnosus, L. curvatus, L. fermentum and L. perolens. All the strains studied tolerated 25 ppm lysozyme, and most of them showed resistance to 0.3% bile. After incubation in gastric solution (pH 2.0), counts decreased by several logs, ranging from 3.2 to 7.0. The strains were able to grow in the presence of bile salts, but only three isolates were capable of deconjugation. The non-starter lactobacilli assayed fermented prebiotic substrates (especially lactulose and inulin). Some strains showed high cell hydrophobicity and b-galactosidase activity, as well as inhibitory activity against pathogenic bacteria. It was concluded that most of the lactobacilli isolated in this work demonstrated resistance to biological barriers and physiological characteristics compatible with probiotic properties, which make them suitable for further research in in vivo studies aimed to identify new probiotic organisms.

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