Vancomycin-resistant enterococci exploit antibiotic-induced innate immune deficits

Abstract

Infection with antibiotic-resistant bacteria, such as vancomycin-resistant Enterococcus (VRE), is a dangerous and costly complication of broad-spectrum antibiotic therapy 1,2 . How antibioticmediated elimination of commensal bacteria promotes infection by antibiotic-resistant bacteria is a fertile area for speculation with few defined mechanisms. Here we demonstrate that antibiotic treatment of mice notably downregulates intestinal expression of RegIIIγ (also known as Reg3g), a secreted C-type lectin that kills Gram-positive bacteria, including VRE. Downregulation of RegIIIγ markedly decreases in vivo killing of VRE in the intestine of antibiotic-treated mice. Stimulation of intestinal Toll-like receptor 4 by oral administration of lipopolysaccharide re-induces RegIIIγ, thereby boosting innate immune resistance of antibiotic-treated mice against VRE. Compromised mucosal innate immune defence, as induced by broad-spectrum antibiotic therapy, can be corrected by selectively stimulating mucosal epithelial Toll-like receptors, providing a potential therapeutic approach to reduce colonization and infection by antibiotic-resistant microbes.Infections caused by highly antibiotic-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA) and VRE, are an increasing menace in hospitalized patients 3,4 . Treatment of serious VRE infections is limited by the paucity of effective antibiotics 5 . VRE colonizes the gastrointestinal tract and it is likely that systemic bloodstream infections are the result of dissemination from the intestine 6 . It has been widely assumed that antibiotic treatment, by eliminating commensal flora, opens intestinal niches and provides increased access to nutrients, thereby enhancing VRE survival and proliferation. Recent studies, however, have demonstrated that commensal microbes in the intestine induce expression of proteins that restrict bacterial survival and growth 7,8 . Thus, whereas commensal microbes may directly restrict VRE proliferation, an alternative hypothesis is that commensal microbes inhibit VRE indirectly by activating mucosal innate immune defenses.Correspondence and requests for materials should be addressed to E.G.P. (Fig. 1b). RegIIIγ is a secreted lectin with potent bactericidal activity against Gram-positive bacteria that is expressed by intestinal epithelial and Paneth cells 7 . Expression of RegIIIγ is dependent on TLR-MyD88-mediated signals in intestinal epithelial cells and is induced by commensal microbes 7,9 . To determine whether RegIIIγ mediates in vivo killing of VRE in the intestine, we injected a blocking polyclonal antiserum 10 against RegIIIγ into ileal loops of wild-type mice before inoculation of VRE. The number of surviving VRE bacteria was increased by over 400% in intestines treated with RegIIIγ-specific antiserum (Fig. 1c), indicating that RegIIIγ mediates in vivo VRE killing.Administration of the broad-spectrum antibiotic combination metronidazole, neomycin and vancomycin (MNV), to which VRE is resistant, markedly increases ...

MyD88 signaling in nonhematopoietic cells protects mice against induced colitis by regulating specific EGF receptor ligands

“…In the setting of an acute infectious intestinal inflammation, we have shown previously for L. monocytogenes and vancomycinresistant Enterococcus faecium that MyD88 signaling plays an important role in nonhematopoietic cells by inducing the antimicrobial molecule RegIIIγ, which is important for defense against Gram-positive bacteria (22,25). In line with these results, we find now that TLR signaling in nonhematopoietic cells is crucial in a model of DSS-induced colitis.…”

“…We considered that the commensal flora might serve as a tonic stimulus for the induction of EGFR ligands AREG and EREG in the intestinal tract. To examine this possibility, the expression of EGFR ligands was measured after the depletion of the flora with antibiotics using vancomycin, neomycin, and metronidazole, administered for 7 d as described previously (22). Administration of broad-spectrum antibiotics significantly diminished the levels of Areg and Ereg but not of Hbegf, Tgf, and Btc transcripts.…”

Nod2 is required for the regulation of commensal microbiota in the intestine

“…Therefore, it is tempting to speculate that mutations in the Nod2 gene in Crohn's disease are associated with changes in the composition and load of the commensal microbiota in the terminal ileum that may facilitate disease progression and pathology. MyD88 also is known to control intestinal infection by pathogenic bacteria such as Listeria monocytogenes or vancomycin-resistant Enterococcus through an increased expression of antimicrobials (32,33). Interestingly, Paneth cell-intrinsic expression of MyD88 has Fresh feces samples were collected from mice at 0, 3, 7, and 14 days after inoculation, and DNA was purified.…”

The regulation of host defences to infection by the microbiota

“…Within the intestine the microbiota stimulates epithelial production of antimicrobial peptides,44, 45, 46 in addition to promoting the antimicrobial activity of immune cells 47. These mechanisms of microbiota‐mediated protection against intestinal infection have been extensively reviewed elsewhere15, 38, 48 and will not be discussed in this article.…”