Modulators of Enterococcus faecalis Cell Envelope Integrity and Antimicrobial Resistance Influence Stable Colonization of the Mammalian Gastrointestinal Tract

The Gram-positive bacterium Enterococcus faecalis is both a colonizer of the gastrointestinal tract (GIT) and an agent of serious nosocomial infections. Although it is typically required for pathogenesis, GIT colonization by E. faecalis is poorly understood. E. faecalis tolerates high concentrations of GIT antimicrobials, like cholate and lysozyme, leading us to hypothesize that resistance to intestinal antimicrobials is essential for long-term GIT colonization. Analyses of E. faecalis mutants exhibiting defects in antimicrobial resistance revealed that IreK, a determinant of envelope integrity and antimicrobial resistance, is required for long-term GIT colonization. IreK is a member of the PASTA kinase protein family, bacterial transmembrane signaling proteins implicated in the regulation of cell wall homeostasis. Among several determinants of cholate and lysozyme resistance in E. faecalis, IreK was the only one found to be required for intestinal colonization, emphasizing the importance of this protein to enterococcal adaptation to the GIT. By studying.ireK suppressor mutants that recovered the ability to colonize the GIT, we identified two conserved enterococcal proteins (OG1RF_11271 and OG1RF_11272) that function antagonistically to IreK and interfere with cell envelope integrity, antimicrobial resistance, and GIT colonization. Our data suggest that IreK, through its kinase activity, inhibits the actions of these proteins. IreK, OG1RF_11271, and OG1RF_11272 are found in all enterococci, suggesting that their effect on GIT colonization is universal across enterococci. Thus, we have defined conserved genes in the enterococcal core genome that influence GIT colonization through their effect on enterococcal envelope integrity and antimicrobial resistance.