Safety and intestinal microbiota modulation by the exopolysaccharide-producing strains Bifidobacterium animalis IPLA R1 and Bifidobacterium longum IPLA E44 orally administered to Wistar rats

Abstract

Bifidobacterium animalis subsp. lactis IPLA R1 and Bifidobacterium longum IPLA E44 strains were tested in vivo for their safety and ability to modulate the intestinal microbiota. Chemically simulated gastrointestinal digestion showed a considerably lower survival of E44 than R1 strain, the first microorganism being also more sensitive to the refrigerated storage in 10%-skimmed milk at 4ºC. Male Wistar rats 12 weeks-old were distributed into three groups, eight rats each. Two groups were daily administered 108 to 109 cfu of the corresponding strain suspended in 10%-skimmed milk during 24 days whereas rats in the placebo group received skimmed milk without microorganisms added. The microbiota and short chain fatty acids (SCFA) were monitored daily in faeces during treatment and in caecum-content at the end of the assay. Quantitative real-time PCR (qPCR) showed that faecal and caecal Bifidobacterium levels were higher in bifidobacteria-fed than in the placebo rats at the end of the intervention whereas total anaerobic-plate counts did not show significant differences. Quantification of B. animalis and B. longum by q-PCR evidenced that, independently on the microorganism administered, treatment with bifidobacteria resulted in higher levels of B. animalis in the caecum. PCR-DGGE analysis of microbial populations revealed a higher diversity of bands in caecum-content of rats fed B. animalis IPLA R1 than in the placebo and rats fed B. longum IPLA E44. Remarkably, although no variations in the proportion of acetate, propionate and butyrate were found, at the end of the assay total SCFA concentration in faeces of rats fed bifidobacteria were significantly higher and those in caecum-content significantly lower than that of the placebo group, suggesting a displacement of the SCFA production to parts in the intestine more distal that caecum in rats receiving bifidobacteria. Harmful glycosidic activities were absent or at low levels in the strains R1 and E44. Both strains were sensitive to most antibiotics although, similarly to some other bifidobacteria strains, they displayed a moderate resistance against tetracycline which in the case of R1correlated with the presence of tet (W) gene. The general parameters indicating well-being status as well as translocation to different organs and histological examination of the gut tissues revealed no changes induced by the administration of bifidobacteria. Therefore, the oral administration of B. animalis IPLA R1 and B. longum E44 can be considered safe, these microorganisms having the ability to modulate the intestinal microbiota of rats by influencing SCFA and the bifidobacterial population levels.