Genetic heterogeneity and functional properties of intestinal bifidobacteria

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Abstract
The aim of the present study was to compare several molecular methods for the identification and genotyping of bifidobacteria, and further to investigate genetic heterogeneity and functional properties of bifidobacterial isolates from intestinal samples of Finnish adult subjects. A total of 153 intestinal bifidobacterial isolates were included in initial screening and 34 isolates were further characterized. Identification results obtained with PCR-ELISA and ribotyping were well in accordance with each other, while randomly amplified polymorphic DNA (RAPD) gave tentative identification only to Bifidobacterium bifidum and to 65% of the B. longum isolates. The most commonly detected species were B. longum biotype longum followed by B. adolescentis and B. bifidum. In addition, B. animalis (lactis), B. angulatum and B. pseudocatenulatum were found. Ribotyping and pulsed-field gel electrophoresis (PFGE) proved to be discriminatory methods for bifidobacteria, but also RAPD revealed intraspecies heterogeneity. Besides two B. animalis (lactis) isolates with very close similarity to a commercially available probiotic strain, none of the intestinal isolates showed optimal survival in all tolerance (acid, bile and oxygen) or growth performance tests. Several species/strains of bifidobacteria simultaneously colonize the gastrointestinal tract of healthy Finnish adults and intestinal Bifidobacterium isolates were genetically heterogeneous. Functional properties of bifidobacteria were strain-dependent. Applicability of ribotyping with the automated RiboPrinter System for identification and genotyping of bifidobacteria was shown in the present study.