PCR detection of Bifidobacterium strains and Streptococcus thermophilus in feces of human subjects after oral bacteriotherapy and yogurt consumption

Streptococcus thermophilus, Bifidobacterium infantis Y1 and Bifidobacterium breve Y8 strains were identified and enumerated by PCR assay in human fecal samples after intake of the pharmaceutical preparation VSL-3 or yogurt. ThI/ThII primer set, specific for S. thermophilus, was selected testing its specificity against several strains of enterococci, streptococci and other genera colonizing the human intestine. A culture-independent PCR protocol, developed in this study, allowed to directly detect and enumerate S. thermophilus in human feces, excluding culture-based techniques or time consuming DNA isolation and purification procedures. Intestinal persistence of S. thermophilus was studied in feces of 10 healthy subjects given VSL-3 or yogurt. Streptococcal population was detected after 3 days of administration and persisted for 6 days after the treatment suspension. In the same trial, the colonization kinetics of B. infantis Y1 and B. breve Y8 were studied by amplification of colonies with the strain-specific primer sets InfY-BV.L/R and BreY-BV.R/L, showing a host-dependent transient colonization behaviour. PCR analysis of feces from 10 patients affected by inflammatory bowel diseases (IBD) and treated with VSL-3 for 2 months showed a colonization pattern of S. thermophilus, B. infantis Y1 and B. breve Y8 similar to that observed with the healthy subjects.