High prevalence of aggregative adherent Escherichia coli strains in the mucosa-associated microbiota of patients with inflammatory bowel diseases

The intestinal population of Escherichia coli is increased in patients with inflammatory bowel disease (IBD), but the reason for this elevation, the particular features of these bacteria and their potential role in the pathogenesis of the disease are not known. The present study was undertaken to investigate the adherence abilities and some virulence properties of a collection of 131 E. coli isolates cultured from rectal biopsies of 23 subjects diagnosed with ulcerative colitis (UC), 8 with Crohn's disease (CD) and 23 control patients from southern Brazil. The adherence abilities of the bacteria were investigated in vitro, using HEp-2 epithelial cells in assays of 3 and 6 h of bacteria–cell contact. The isolates were screened by PCR with primers for the following virulence genetic markers: plasmid of aggregative adhesion (pAA) and the aggregative adherence fimbriae R (aggR), E. coli attaching and effacing (eae), invasion-associated locus (ial), invasion plasmid antigen H (ipaH) and Shiga citotoxin-encoding (stx) genes. HEp-2 cells aggregative adherent E. coli strains, as detected in the 3 h adherence assay, were found in 14/23 (60.9%) patients with UC, 7/8 (87.5%) with CD and in 7/23 (30.4%) controls (p = 0.011). Virulence genetic markers were detected in strains of 9 patients with UC (39.1%), but in none of CD or control group. Two of these UC patients had strains harboring both pAA and aggR, one had strains positive for aggR, four had strains positive for eae and two had strains positive for stx. These results suggest that the augmented population of E. coli on the rectal mucosa of IBD patients, particularly of those diagnosed with UC, is mostly comprised of aggregative adherent strains, some of which possessing classical virulence markers of E. coli.