Culture-dependent and culture-independent qualitative analysis of probiotic products claimed to contain bifidobacteria

A total of 58 probiotic products obtained worldwide, which were claimed to contain Bifidobacterium strains (including 22 yoghurts, 5 dairy fruit drinks, 28 food supplements and 3 pharmaceutical preparations) were investigated in parallel using a culture-dependent and a culture-independent approach. Three isolation media previously reported as selective for Bifidobacterium were evaluated for their suitability in the quality analysis of these products. Subsequently, possible bifidobacterial colonies were picked from the best medium and identified by means of rep-PCR fingerprinting using the BOX primer (BOX-PCR). Bifidobacterium animalis subsp. lactis, formerly classified as Bifidobacterium lactis, was most frequently found, but strains belonging to Bifidobacterium longum biotypes longum and infantis, Bifidobacterium bifidum and Bifidobacterium breve were recovered also. In parallel, all products were also subjected to culture-independent analysis which involved a nested-PCR step on total bacterial DNA extracted directly from the product, followed by separation of the amplicons by Denaturing Gradient Gel Electrophoresis (DGGE) and subsequent identification of species from the band patterns. By conventional cultivation, 70.7% of the products analysed were found to contain culturable bifidobacteria whereas by culture-independent DGGE analysis members of the genus Bifidobacterium could be detected in 96.5% of the analysed products. Genotypic characterization of a number of bifidobacterial isolates at the strain level by means of Pulsed-Field Gel Electrophoresis (PFGE) revealed a relatively high degree of genomic homogeneity among the Bifidobacterium strains currently used in the probiotic industry.