IN VITRO AND IN VIVO STUDY OF GASTROINTESTINAL SURVIVAL OF LACTOBACILLUS CASEI ATCC 393, ADHESION TO INTESTINAL MUCOSA AND MODULATION OF INTESTINAL MICROBIAL FLORA

摘要

Nowadays an upsurge of interest in developing novel foods containing probiotic microorganisms, such as lactic acid bacteria, is observed. Such functional foods have a great potential in promoting human health. In order to deliver the health benefits, probiotics need to contain an adequate amount of live bacteria (at least 10~6 cfu/g), able to survive the acidic conditions of the upper gastrointestinal (GI) tract and proliferate in the intestine, a requirement that is not always fulfilled. Since it is well established that cell immobilization enhances the viability of cultures, the aim of the present study was to assess (a) the in vitro and in vivo Gl survival of both free and immobilized L. casei ATCC 393 on apple pieces contained in probiotic fermented milk, (b) the in vivo adhesion to the intestinal mucosa, and (c) 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 in Wistar rats. By 12 h after single dose administration, both free and immobilized cells were detected by microbiological and molecular analysis at levels ≥ 10~6 cfu/g of feces. Moreover, in vivo adhesion of L. casei ATCC 393 at the rat GI tract was detected. Specifically, the adhesion of the probiotic cells at the large intestine (cecum and colon) was recorded at levels ≥ 10~6 cfu/g (suggested minimum levels for conferring a probiotic effect) following daily administration for 7 days. Their levels were lower at the small intestine (duodenum, jejunum and ileum) (≤ 10~3 cfu/g), indicating that adhesion was a targeted process. The colonization of the GI tract detected by multiplex PCR was transient. Thus, daily consumption of probiotic products containing the specific strain appears to be a prerequisite for retaining its levels at an effective concentration, information that could be valuable for the food industry. Finally, daily administration of the probiotic products led to significant reduction of staphylococci, enterobacteria, coliforms and streptococci counts in rat feces. In conclusion, L. casei ATCC 393 contained in fermented milk survived GI transit, adhered to the intestinal mucosa and modulated intestinal microbiota.