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 ofthe gastrointestinal tract (GIT) and an agent of serious nosocomial infections. Althoughit is typically required for pathogenesis, GIT colonization by E. faecalis ispoorly understood. E. faecalis tolerates high concentrations of GIT antimicrobials, likecholate and lysozyme, leading us to hypothesize that resistance to intestinal antimicrobialsis essential for long-term GIT colonization. Analyses of E. faecalis mutants exhibitingdefects in antimicrobial resistance revealed that IreK, a determinant of envelopeintegrity and antimicrobial resistance, is required for long-term GIT colonization.IreK is a member of the PASTA kinase protein family, bacterial transmembrane signalingproteins implicated in the regulation of cell wall homeostasis. Among severaldeterminants of cholate and lysozyme resistance in E. faecalis, IreK was the only onefound to be required for intestinal colonization, emphasizing the importance of thisprotein to enterococcal adaptation to the GIT. By studying ΔireK suppressor mutantsthat recovered the ability to colonize the GIT, we identified two conserved enterococcalproteins (OG1RF_11271 and OG1RF_11272) that function antagonistically toIreK and interfere with cell envelope integrity, antimicrobial resistance, and GIT colonization.Our data suggest that IreK, through its kinase activity, inhibits the actionsof 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 influenceGIT colonization through their effect on enterococcal envelope integrity andantimicrobial resistance.