Mannose-specific interactions of Lactobacillus plantarum in the intestine : bacterial genes, molecular host responses and potential probiotic effects

One potential mechanism by which probiotic microorganisms may exert beneficial health effects to the host is the inhibition of intestinal infections by competitive exclusion of pathogenic bacteria. This concept may also be applicable for mannose-specific adhesion to the epithelial surface, which has been demonstrated for several pathogens as well as for the probiotic Lactobacillus plantarum. In this thesis, a complementary approach was performed to focus on mannose-specific host-microbe interactions of L. plantarum in the intestine. Firstly, the mannose-specific adhesin encoding gene (msa) of L. plantarum was identified using an in vitro biodiversity-based approach including genotype-phenotype matching and subsequent mutagenesis analysis. The domain composition of the encoded protein Msa was further characterized in selected L. plantarum strains, revealing strain-specific variations in domain composition. Secondly, intestinal host responses as reflected in differential gene expression patterns induced by L. plantarum 299v wildtype and its isogenic msa-deletion derivative were investigated using DNA microarrays. In an in situ Small Intestinal Segment Perfusion model in pigs, increased mRNA expression of pancreatitis-associated protein, a protein with antibacterial activity, was caused by the wildtype strain only. In vivo, transcriptome profiles induced by oral administration of L. plantarum 299v wildtype and the msa-mutant strain were found to be different in pigs, corroborating a role for Msa in host-microbe interactions. Finally, potential probiotic effects of L. plantarum 299v wildtype strain based on competitive exclusion of pathogens at mannose-specific binding sites on the intestinal epithelium were studied in different animal models. However, these studies did not provide clear evidence on measurable probiotic effects related to mannose adhesion. Apparently, mannose-specific interactions only play a limited role in competitive exclusion mechanisms and total persistence properties of L. plantarum in the gut. Nevertheless, since Msa was found to induce particular host responses in epithelial cells this protein seems to be one of the factors that mediate part of the complex host-bacterial interplay in the intestine by facilitating temporary contact with the epithelium. This thesis contributes to multi-dimensional investigations of host-probiotic interactions on a molecular level, which are needed for a better understanding of probiotic modes of action and an improved future development of next generation probiotics with targeted and optimized functionality for particular health benefits