title: Surface-Associated Lipoproteins Link Enterococcus faecalis Virulence to Colitogenic Activity in IL-10-Deficient Mice Independent of Their Expression Levels.
abstract: The commensal Enterococcus faecalis is among the most common causes of nosocomial infections. Recent findings regarding increased abundance of enterococci in the intestinal microbiota of patients with inflammatory bowel diseases and induction of colitis in IL-10-deficient (IL-10-/-) mice put a new perspective on the contribution of E. faecalis to chronic intestinal inflammation. Based on the expression of virulence-related genes in the inflammatory milieu of IL-10-/- mice using RNA-sequencing analysis, we characterized the colitogenic role of two bacterial structures that substantially impact on E. faecalis virulence by different mechanisms: the enterococcal polysaccharide antigen and cell surface-associated lipoproteins. Germ-free wild type and IL-10-/- mice were monoassociated with E. faecalis wild type OG1RF or the respective isogenic mutants for 16 weeks. Intestinal tissue and mesenteric lymph nodes (MLN) were collected to characterize tissue pathology, loss of intestinal barrier function, bacterial adhesion to intestinal epithelium and immune cell activation. Bone marrow-derived dendritic cells (BMDC) were stimulated with bacterial lysates and E. faecalis virulence was additionally investigated in three invertebrate models. Colitogenic activity of wild type E. faecalis (OG1RF score: 7.2±1.2) in monoassociated IL-10-/- mice was partially impaired in E. faecalis lacking enterococcal polysaccharide antigen (ΔepaB score: 4.7±2.3; p<0.05) and was almost completely abrogated in E. faecalis deficient for lipoproteins (Δlgt score: 2.3±2.3; p<0.0001). Consistently both E. faecalis mutants showed significantly impaired virulence in Galleria mellonella and Caenorhabditis elegans. Loss of E-cadherin in the epithelium was shown for all bacterial strains in inflamed IL-10-/- but not wild type mice. Inactivation of epaB in E. faecalis reduced microcolony and biofilm formation in vitro, altered bacterial adhesion to intestinal epithelium of germ-free Manduca sexta larvae and impaired penetration into the colonic mucus layer of IL-10-/- mice. Lipoprotein-deficient E. faecalis exhibited an impaired TLR2-mediated activation of BMDCs in vitro despite their ability to fully reactivate MLN cells as well as MLN-derived colitogenic T cells ex vivo. E. faecalis virulence factors accounting for bacterial adhesion to mucosal surfaces as well as intestinal barrier disruption partially contribute to colitogenic activity of E. faecalis. Beyond their well-known role in infections, cell surface-associated lipoproteins are essential structures for colitogenic activity of E. faecalis by mediating innate immune cell activation.
authors.affiliation: Technische Universität München, Chair of Nutrition and Immunology, ZIEL-Research Center for Nutrition and Food Sciences, Freising-Weihenstephan, Germany.
authors.forename: Soeren
authors.initials: S
authors.lastname: Ocvirk
authors.affiliation: Technische Universität München, Chair of Nutrition and Immunology, ZIEL-Research Center for Nutrition and Food Sciences, Freising-Weihenstephan, Germany.
authors.forename: Irina G
authors.initials: IG
authors.lastname: Sava
authors.affiliation: Technische Universität München, Chair of Nutrition and Immunology, ZIEL-Research Center for Nutrition and Food Sciences, Freising-Weihenstephan, Germany.
authors.forename: Isabella
authors.initials: I
authors.lastname: Lengfelder
authors.affiliation: Technische Universität München, Chair of Nutrition and Immunology, ZIEL-Research Center for Nutrition and Food Sciences, Freising-Weihenstephan, Germany.
authors.forename: Ilias
authors.initials: I
authors.lastname: Lagkouvardos
authors.affiliation: Technische Universität München, Chair of Nutrition and Immunology, ZIEL-Research Center for Nutrition and Food Sciences, Freising-Weihenstephan, Germany.
authors.forename: Natalie
authors.initials: N
authors.lastname: Steck
authors.affiliation: Division of Infectious Diseases, Department of Internal Medicine, The University of Texas Medical School, Houston, Texas, United States of America.
authors.forename: Jung H
authors.initials: JH
authors.lastname: Roh
authors.affiliation: Division of Gastroenterology and Hepatology, Department of Medicine, University of North Carolina, Chapel Hill, Chapel Hill, North Carolina, United States of America.
authors.forename: Sandrine
authors.initials: S
authors.lastname: Tchaptchet
authors.affiliation: Division of Infectious Diseases, Department of Medicine, University Medical Center Freiburg, Freiburg, Germany.
authors.forename: Yinyin
authors.initials: Y
authors.lastname: Bao
authors.affiliation: Division of Gastroenterology and Hepatology, Department of Medicine, University of North Carolina, Chapel Hill, Chapel Hill, North Carolina, United States of America.
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Hansen
authors.affiliation: Division of Infectious Diseases, Department of Medicine, University Medical Center Freiburg, Freiburg, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Huebner
authors.affiliation: Division of Gastroenterology and Hepatology, Department of Medicine, University of North Carolina, Chapel Hill, Chapel Hill, North Carolina, United States of America.
authors.forename: Ian M
authors.initials: IM
authors.lastname: Carroll
authors.affiliation: Division of Infectious Diseases, Department of Internal Medicine, The University of Texas Medical School, Houston, Texas, United States of America.
authors.forename: Barbara E
authors.initials: BE
authors.lastname: Murray
authors.affiliation: Division of Gastroenterology and Hepatology, Department of Medicine, University of North Carolina, Chapel Hill, Chapel Hill, North Carolina, United States of America.
authors.forename: R Balfour
authors.initials: RB
authors.lastname: Sartor
authors.affiliation: Technische Universität München, Chair of Nutrition and Immunology, ZIEL-Research Center for Nutrition and Food Sciences, Freising-Weihenstephan, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Haller
mesh_terms: D000818:Animals; D015153:Blotting, Western; D003092:Colitis / Q000382:microbiology*; D013293:Enterococcus faecalis / Q000276:immunology* / Q000378:metabolism / Q000472:pathogenicity*; D005455:Fluorescent Antibody Technique; D016908:Gram-Positive Bacterial Infections / Q000276:immunology / Q000378:metabolism*; D017404:In Situ Hybridization, Fluorescence; D016753:Interleukin-10 / Q000172:deficiency / Q000378:metabolism*; D008074:Lipoproteins / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D014774:Virulence
chemical_list: C556062:IL10 protein, mouse; D008074:Lipoproteins; D016753:Interleukin-10