Date Published: January 24, 2013
Publisher: Public Library of Science
Author(s): Nicolas Dreux, Jérémy Denizot, Margarita Martinez-Medina, Alexander Mellmann, Maria Billig, Dagmara Kisiela, Sujay Chattopadhyay, Evgeni Sokurenko, Christel Neut, Corinne Gower-Rousseau, Jean-Frédéric Colombel, Richard Bonnet, Arlette Darfeuille-Michaud, Nicolas Barnich, Matthew A. Mulvey.
Adherent-invasive Escherichia coli (AIEC) are abnormally predominant on Crohn’s disease (CD) ileal mucosa. AIEC reference strain LF82 adheres to ileal enterocytes via the common type 1 pili adhesin FimH and recognizes CEACAM6 receptors abnormally expressed on CD ileal epithelial cells. The fimH genes of 45 AIEC and 47 non-AIEC strains were sequenced. The phylogenetic tree based on fimH DNA sequences indicated that AIEC strains predominantly express FimH with amino acid mutations of a recent evolutionary origin – a typical signature of pathoadaptive changes of bacterial pathogens. Point mutations in FimH, some of a unique AIEC-associated nature, confer AIEC bacteria a significantly higher ability to adhere to CEACAM-expressing T84 intestinal epithelial cells. Moreover, in the LF82 strain, the replacement of fimHLF82 (expressing FimH with an AIEC-associated mutation) with fimHK12 (expressing FimH of commensal E. coli K12) decreased the ability of bacteria to persist and to induce severe colitis and gut inflammation in infected CEABAC10 transgenic mice expressing human CEACAM receptors. Our results highlight a mechanism of AIEC virulence evolution that involves selection of amino acid mutations in the common bacterial traits, such as FimH protein, and leads to the development of chronic inflammatory bowel disease (IBD) in a genetically susceptible host. The analysis of fimH SNPs may be a useful method to predict the potential virulence of E. coli isolated from IBD patients for diagnostic or epidemiological studies and to identify new strategies for therapeutic intervention to block the interaction between AIEC and gut mucosa in the early stages of IBD.
The molecular pathogenesis of inflammatory bowel disease (IBD), a chronic inflammation of the digestive tract, remains poorly understood. However, current evidence suggests that Crohn’s disease (CD) pathogenesis involves interactions between the intestinal microbiome and the immune system, including important contributions from genetic and environmental risk factors with microorganisms playing a central role , . Of the bacteria that may play a role in the pathogenesis of CD, a pathovar of E. coli called AIEC, for adherent-invasive Escherichia coli, has been strongly implicated in IBD, particularly in CD , , , , , . AIEC are able to adhere to the intestinal epithelium and colonize gut mucosa. They invade intestinal epithelial cells and macrophages and are able to replicate intracellularly without inducing cell death or INFγ secretion by infected macrophages. AIEC were found to be associated with ileal mucosa in 36.4% of CD patients compared with 6.2% of controls , suggesting that these bacteria are involved in CD pathogenesis. AIEC are distinct from other pathogenic intestinal E. coli strains because they do not harbor genes typically associated with pathogens such as enterotoxigenic, enterohemorrhagic, enteroinvasive, enteroaggregative, and enteropathogenic E. coli, . AIEC bacteria adhere specifically to carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6), which is abnormally expressed in the ileal mucosa of 35% of CD patients, via FimH, the terminal subunit of the type 1 pilus .
Abnormal expression of CEACAM6 is observed at the apical surface of the ileal epithelium in CD patients, and CD ileal lesions are colonized by pathogenic adherent-invasive Escherichia coli (AIEC) , . CD-associated AIEC colonize and induce strong gut inflammation in transgenic mice expressing human CEACAMs, which act as a receptor for type 1 pili produced by AIEC bacteria , . AIEC also induce CEACAM6 expression by intestinal epithelial cells directly by adhering to host cells and indirectly via increased secretion of TNF-α from AIEC-infected macrophages. Our hypothesis was that abnormal expression of CEACAM6 in the ileal mucosa of CD patients can select for E. coli strains harboring pathoadaptive mutations in FimH adhesin that enhance binding to mannosylated receptors. Knowledge of fimH polymorphisms is critical for our understanding of the mechanisms of AIEC gut colonization in CD patients and for efforts to develop novel therapeutic strategies. Indeed, as observed with uropathogenic E. coli (UPEC) in the context of urinary infections , blocking the interaction between type 1 pili and CEACAM molecules might serve as a specific means of disrupting colonization and the subsequent inflammatory amplification loop.