Impact of consumption of probiotic lactobacilli-containing yogurt on microbial composition in human feces

An in vivo study was carried out to determine the effect of consuming probiotic lactobacilli-containing yogurt on the composition of microbiota in the human gut. Fifteen healthy adults ingested a daily serving of one of three commercial yogurts (two of the products contained a probiotic lactobacilli strain) for 20 days. Fecal samples at defined time points before, during, and after the period of yogurt ingestion were collected and analyzed. The fecal population of lactobacilli was determined by a culture-based method and subsequent colony PCR for the identification of species. Six predominant bacterial groups in the fecal samples were quantitatively determined based on a sequence-specific SSU rRNA cleavage method coupled with a suite of oligonucleotide probes, which was optimized for the target-specific detection of bacterial groups inhabiting human feces. In the ingestion period, one probiotic strain was detected in the feces of all five subjects who consumed the yogurt containing the strain, while the other strain was detected in three of another five subjects. The population levels of the two major groups (Bacteroides and Prevotella, and the Clostridium coccoides–Eubacterium rectale group) in the fecal samples tended to change in response to the ingestion but the change did not seem to be dependent on the product-specific property of each yogurt. These results suggest that the human fecal bacterial community could be altered by ingesting yogurt, although whether probiotic lactobacilli are present or absent in the yogurt does not seem to be a factor in this change.