Enterococcal bacteremia in mice is prevented by oral administration of probiotic Bacillus spores.

Harnessing one bacterium to defeat another: Enterococcus faecalis is a frequently antibiotic-resistant pathogen that can cause blood infection after antibiotic-induced overgrowth in the gut. Piewngam et al. now show that translocation of E. faecalis across the mouse gut epithelium into the bloodstream is dependent on a specific mechanism of bacterial signaling that can be blocked by probiotic Bacillus subtilis spores administered orally. B. subtilis, which is commercially available, may hold promise for preventing systemic infection by E. faecalis particularly in at-risk populations, such as hospitalized and immune-depleted patients undergoing antibiotic therapy. Whether and how probiotics promote human health is a controversial issue. Their claimed benefit for counteracting gastrointestinal infection is linked predominantly to reducing pathogen abundance within the intestinal microbiota. Less understood mechanistically is the reported value that probiotics could have in reducing systemic infections. Enterococcus faecalis is an opportunistic pathogen that causes systemic infection after translocation through the intestinal epithelium, particularly in hospitalized and immune-depleted patients receiving antibiotic therapy. In this study, we used an E. faecalis mouse infection model with wild-type and isogenic mutant strains deficient in genes of the E. faecalis Fsr (fecal streptococci regulator) quorum-sensing system. We show that E. faecalis translocation from the mouse gut into the blood is mediated by the Fsr quorum-sensing system through production of the protease GelE, which compromises intestinal epithelium integrity. Furthermore, we demonstrate that orally administered probiotic Bacillus subtilis spores blocked E. faecalis translocation from the gut to the bloodstream and subsequent systemic infection in mice by inhibiting Fsr activity. These findings demonstrate that a key aspect of Enterococcus pathogenesis is controlled by quorum sensing, which can be targeted with probiotic Bacillus spores. [ABSTRACT FROM AUTHOR]

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