Genome-based Definition of an Inflammatory Bowel Disease-associated Adherent-Invasive Escherichia coli Pathovar.

Background: Mucosal-associated Escherichia coli are commonly found in inflamed tissues during inflammatory bowel disease (IBD). These bacteria often possess an adherent and invasive phenotype but lack virulence-associated features of well-described intestinal E. coli pathogens, and are of diverse serology and phylotypes, making it difficult to correlate strain characteristics with exacerbations of disease.

Methods: The genome sequences of 14 phenotypically assigned adherent-invasive Escherichia coli (AIEC) isolates obtained from intestinal biopsies of patients with IBD were compared with the genome sequences of 37 other pathogenic and commensal E. coli available from public databases.

Results: Core genome-based phylogenetic analyses and genome-wide comparison of genetic content established the existence of a closely related cluster of AIEC strains with 3 distinct genetic insertions differentiating them from commensal E. coli. These strains are of the B2 phylotype have a variant type VI secretion system (T6SS-1), and are highly related to extraintestinal pathogenic E. coli, suggesting that these 2 clinically distinct pathovars have common virulence strategies. Four other mucosally adherent E. coli strains from patients with IBD were of diverse phylogenetic origins and lacked the 3 genetic features, suggesting that they are not related to the B2 AIEC cluster. Although AIEC are often considered as having a unique association with Crohn's disease, isolates from Crohn's disease and ulcerative colitis were genetically indistinguishable.

Conclusions: B2 AIEC thus represent a closely related cluster of IBD-associated E. coli strains that are distinct from normal commensal isolates, and which should be considered separately from the phenotypically similar but genetically distinct non-B2 AIEC strains when considering their association with intestinal pathogenesis.