Comparative effects of exopolysaccharides from lactic acid bacteria and fructo-oligosaccharides on infant gut microbiota tested in an in vitro colonic model with immobilized cells.

The aim of this study was to compare the effects of purified exopolysaccharides from Lactobacillus rhamnosus RW-9595M with those of a well-known prebiotic (short-chain fructo-oligosaccharides) on infant colonic microbiota using a new three-stage chemostat model with immobilized infant faecal microbiota. Two continuous cultures with different faecal inocula were tested with different compositions of carbohydrate media. During the first fermentation (F1), fructo-oligosaccharides tested at a concentration of 9.8 g L(-1) increased the number of lactobacilli and decreased coliforms both in gel beads and in effluent from all three reactors, in agreement with data from the literature. During the second fermentation (F2), the effect of fructo-oligosaccharides tested at a lower concentration (7.5 g L(-1)) was reduced compared with F1. Fructo-oligosaccharides also increased total organic acid concentration and decreased ammonia production. Results obtained for exopolysaccharide tested at 1.5 g L(-1) indicate that exopolysaccharides from L. rhamnosus RW-9595M was not metabolized by infant microbiota and lacked any prebiotic effect.

New three-stage in vitro model for infant colonic fermentation with immobilized fecal microbiota.

The development and validation of a new three-stage culture system with immobilized fecal microbiota to simulate infant colonic ecosystem is described. Two continuous cultures with different fecal inocula were used to assess the validity and stability of the intestinal model. The total anaerobe populations measured in beads and effluent fermentations reached high concentrations similar to infant feces. Fluorescence in situ hybridization analyses and denaturing gradient gel electrophoresis profiles of effluent samples from the three reactors revealed complex patterns similar to that observed in the inoculum, indicating that fecal bacterial diversity was well-preserved and that dominant bacterial populations showed good stability among reactors. For both experiments, the bacterial populations and fermentation product concentrations were in the range of published data for infant feces. These results demonstrate that this new three-stage continuous culture with immobilized cells provides a useful tool for studying the infant colon ecosystem.