Specific detection of Bifidobacterium strains in a pharmaceutical probiotic product and in human feces by polymerase chain reaction

For PCR specific detection of the strains Bifidobacterium longum Y 10, B. i nfantis Y 1 and B. breve Y 8 used in a new probiotic product (VSL-3), strai ns-specific rDNA primers have been developed. Spacer regions between the 16 S and 23S rRNA genes (ITS) of the three strains were amplified by PCR with conserved primers and the nucleotide sequence of these ITSs were determined . On the basis of their comparison with the rDNA sequences retrieved from G enBank, we designed new primers which specifically recognize the species B. breve and the two strains B. infantis Y 1 and B. breve Y 8. Specificity of these primers was confirmed through the analysis of 60 bifidobacteria stra ins belonging to the more representative human species. The feasibility of this PCR method was investigated in commercial VSL-3 product and fecal samp les collected from 4 patients affected by inflammatory bowel deseases and t wo healthy subjects before and after the VSL-3 administration. By PCR analy sis of different VSL-3 commercial batches we were successful in differentia ting and quantifying the strains B. longum Y 10, B. infantis Y 1 and B, bre ve Y 8. B. infantis Y 1 and B. breve Y 8 could be detected at high concentr ation in fecal specimens of both patients and subjects treated with the pro biotic preparation, showing a different colonization behaviour. Seven days after the VSL-3 treatment suspension, no patients and subjects harbored B. infantis Y 1 and B. breve Y 8, indicating a transient presence of these exo genous strains.