THE PROBIOTIC BACTERIUM LACTOBACILLUS RHAMNOSUS GG ELIMINATES HUMAN GUT PATHOGENS BY THE SECRETION OF A GLYCOSIDE HYDROLASE FOLLOWING EXPOSURE TO GLUCOSE

The human microbiota includes beneficial and photogenic microorganisms that compete for the same niche. In many cases interaction between species can lead to inhibition or elimination of one of the species involved in the interaction. Lactobacillus rhamnosus GG is a Gram positive beneficial bacterium that is naturally found in the human intestinal tract and its application as probiotics provides numerous benefits for human health. Our results indicated that a strong antagonistic activity of Lactobacillus rhamnosus GG is exerted towards the pathogens Enterococcus faecalis and Salmonella typhimurium sharing the same niche. This antagonistic interaction depends on the presence and concentration of glucose, and mediated by fermentation acidic products and two acid-resistant effector proteins: glycoside hydrolase and an uncharacterized protein targeting both Gram-positive and Gram-negative pathogens. Interestingly, these effectors are only secreted following the differentiation of the Lactobacillus cells. Our results also demonstrate that Lactobacillus rhamnosus GG changes significantly its interaction with the environment following exposure to glucose, and produces extracellular membrane vesicles in addition to the protein toxins. Collectively, our results provide an appealing explanation to the effects of nutrition on the elimination of pathogens by the probiotic bacteria.