Probiotics are bacteria that are added to functional foods to improve the consumer’s health. It is claimed that these products increase the resistance to intestinal infections, but the underlying mechanisms are often not known. One possible mechanism could be that probiotics compete with pathogenic bacteria for mannose-containing attachment sites on the intestinal surface. The aim of this project was to study in vitro and in animal models how probiotics bind to mannose, which host reactions are induced by that, and whether mannose-specific adhesion really leads to decreased numbers of pathogenic bacteria in the gut.
Firstly, the gene that is responsible for mannose-specific adhesion of the probiotic Lactobacillus plantarum was identified. This is one of the first known “probiotic genes”. The structure of this gene varies even in closely related L. plantarum strains that differ in their ability to attach to mannose. Furthermore, it was found that mannose-specific interactions with L. plantarum switch on the expression of several genes in the intestine of pigs, possibly in order to protect the mucous membrane against increased bacterial contact. Finally, it was shown that mannose-specific attachment of L. plantarum neither leads to its permanent presence in the intestine nor to a decrease in the number of intestinal pathogens.
The findings of these studies do not support the assumption that probiotics can prevent mannose-binding of pathogenic bacteria in the gut. However, the results demonstrate that mannose-specific interactions with L. plantarum directly influence the functionality of intestinal cells.
Complementary approaches as used in this project will increase our knowledge about the molecular mechanisms of probiotics and their health effects. These may be used to better understand the activity of current probiotics and to develop new generation probiotics with targeted and optimized characteristics.
Title thesis: "Mannose-specific interactions of Lactobacillus plantarum in the intestine. Bacterial genes, molecular host responses, and potential probiotic effects"