To date, there is significant controversy as to the survival of yogurt bacteria (namely, Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus) after passage through the human gastrointestinal tract. Survival of both bacterial species in human feces was investigated by culture on selective media. Out of 39 samples recovered from 13 healthy subjects over a 12-day period of fresh yogurt intake, 32 and 37 samples contained viable S. thermophilus (median value of 6.3 x 10(4) CFU g(-1) of feces) and L. delbrueckii (median value of 7.2 x 10(4)CFU g(-1) of feces), respectively. The results of the present study indicate that substantial numbers of yogurt bacteria can survive human gastrointestinal transit.

Probiotics have been the subject of intensive research, mainly focusing on bifidobacteria and lactic acid bacteria. However, there is evidence that dairy propionibacteria also display probiotic properties, which as yet have been underestimated. The aim of this paper is to review recent data which report probiotic characteristics of dairy propionibacteria and to distinctly organise them based on the experimental strategy employed: ranked from in vitro evidence to in vivo trials, which is a new approach. In addition to the selection criteria for probiotics in areas such as food safety, technological and digestive stress tolerance, many potential health benefits have been described which include modulation of microbiota and metabolic activity in the gut, modulation of intestinal motility and absorption, impact on intestinal inflammation, modulation of the immune system and potential modulation of risk factors for cancer development. The robust nature of dairy propionibacteria towards technological stresses should allow their future use in various fermented probiotic foods. Among the probiotic properties of dairy propionibacteria described in the literature, some of these properties are different from those reported for bifidobacteria and lactic acid bacteria. However, supplementation with dairy propionibacteria in randomised, placebo-controlled, double

A human trial was carried out to assess the ileal and fecal survival of Lactobacillus casei DN-114 001 ingested in fermented milk. Survival rates were up to 51.2% in the ileum and 28.4% in the feces. The probiotic bacterium has the capacity to survive during its transit through the human gut.

The present study demonstrates for the first time the transfer of vancomycin resistance (vanA cluster) from enterococci to a Lactobacillusacidophilus commercial strain. Transfers were observed in vitro, but also in vivo in the gut of mice (in the absence of antibiotic pressure) where transconjugants arose at relatively high frequencies and could persist in the digestive environment. Since transfer of vancomycin resistance genes might also take place in the human digestive tract, lactobacilli probiotics should be carefully considered especially in either immunocompromised patients or during antibiotherapy. Acquisition and retransfer of resistance genes should be addressed in the safety evaluation of probiotics.

The overall results support the notion that the in vitro model underestimates the transfer potential. Rapid transfer of vanA plasmids from poultry- and pig-derived strains to human faecal E. faecium shows that even transiently colonizing strains may provide a significant reservoir for transfer of resistance genes to the permanent commensal flora. Newly acquired resistance genes may be stabilized and persist in new populations in the absence of antibiotic selection.