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 ?ireK 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.

革兰氏阳性菌粪肠球菌（Enterococcus faecalis）既是胃肠道（GIT）的定植菌，也是严重医院获得性感染的病原菌。尽管其在致病过程中通常不可或缺，但人们对粪肠球菌在胃肠道的定植机制仍知之甚少。粪肠球菌可耐受胃肠道内高浓度的抗菌物质，如胆盐与溶菌酶，这促使我们提出假说：对肠道抗菌物质的抗性是长期胃肠道定植的必要条件。对粪肠球菌抗菌抗性缺陷突变体的分析显示，包膜完整性与抗菌抗性的决定因子IreK是长期胃肠道定植所必需的。IreK属于PASTA激酶蛋白家族，是一类参与调控细胞壁稳态的细菌跨膜信号蛋白。在粪肠球菌诸多介导胆盐与溶菌酶抗性的因子中，IreK是唯一被发现与肠道定植相关的蛋白，这凸显了该蛋白在肠球菌适应胃肠道环境中的重要性。通过研究恢复了胃肠道定植能力的ΔireK抑制突变体，我们鉴定出两个保守的肠球菌蛋白（OG1RF_11271与OG1RF_11272），它们可与IreK拮抗，并干扰细胞包膜完整性、抗菌抗性以及胃肠道定植。我们的数据表明，IreK通过其激酶活性抑制这两种蛋白的功能。IreK、OG1RF_11271与OG1RF_11272存在于所有肠球菌中，提示它们对胃肠道定植的影响在肠球菌属中具有普遍性。因此，我们明确了肠球菌核心基因组中一类通过影响包膜完整性与抗菌抗性来调控胃肠道定植的保守基因。