Effect of probiotic-fermented milk administration on gastrointestinal survival of Lactobacillus casei ATCC 393 and modulation of intestinal microbial flora.

The aim of the present study was to assess the survival of free and immobilized Lactobacillus casei ATCC 393 on apple pieces, contained in probiotic-fermented milk, after gastrointestinal (GI) transit and to investigate the potential regulation of intestinal microbial flora in a rat model. In in vitro GI stress tolerance tests, immobilized L. casei ATCC 393 exhibited significantly higher survival rates compared to free cells. At a second stage, probiotic-fermented milk produced by either free or immobilized cells was administered orally at a single dose or daily for 9 days in Wistar rats. By 12 h after single-dose administration, both free and immobilized cells were detected by microbiological and molecular analysis at levels ≥6 logCFU/g of feces. Moreover, daily administration led to significant reduction of staphylococci, enterobacteria, coliforms and streptococci counts. In conclusion, L. casei ATCC 393 contained in fermented milk survived GI transit and modulated intestinal microbiota.