Ileal adhesion of virulent E. coli LF82 is not enhanced in Crohn’s disease

Abstract

Adherent-invasive Escherichia coli (AIEC) comprise a new group of E. coli species named from their distinctive ability to adhere to and invade the intestinal epithelium. The AIEC strains have been associated to the ileal mucosa in Crohn’s disease (CD), and the impact of AIEC in the pathogenesis of CD has been further strengthened from the evidence that the ileum in CD harbors an abnormally high number of E. coli species. S16 2010 IBD Abstracts The aim of this study was to examine the adhesion of the AIEC reference strain, LF82, to tissue samples from ileum and colon in CD and healthy controls. A second purpose was to assess the probiotic efficacy of E. coli Nissle 1917 (ECN) in averting LF82 adhesion to ileal mucosa. Ileal and colonic specimens were obtained from patients with CD ileitis and controls (n¼10). A model was developed to investigate bacterial adhesion to intestinal biopsies and comprised: 1) incubation of tissue (inclusive of mucous) with 107 bacteria or buffer for 1 hour, 2) removal of non-adhered bacteria by extensive washing, and 3) absolute quantification of tissue-adhered LF82 and indigenous E. coli by a pre-validated assay including quantitative real-time PCR. Selective primers- and probes were designed specifically for targeting the pMT1-like plasmid in LF82 and E. coli 16S ribosomal DNA for quantifying the general E. coli population. Bacterial numbers were related to tissue weight. A thoroughly validated model with a coefficient of variation <2 % was developed and employed for investigation of the bacterial adherence to human intestinal specimens. LF82 adhered to intestinal biopsies in both CD and controls. Enhanced adhesion was, however, not observed in the ileum as compared to the colon in CD, which was in contradiction to controls that had a significantly higher LF82-attachment to the ileal epithelium as compared to that of the colon (P <0.01). The variation in LF82 adhesion between ileal and colonic specimens was more prominent in CD than in controls. Although not statistically significant, a trend towards higher counts of indigenous E. coli was observed in the ileum as compared to the colon of CD, and the number of indigenous LF82 and total E. coli bacteria tended to be inversely correlated in both ileum and colon tissue. Further, ECN did not avert the adhesion of LF82 to ileal specimens, but instead ECN likely favoured LF82 adhesion particularly in CD. ECN did also adhere to the ileal mucosa. Conclusively it was shown that LF82 preferentially adhere to ileal tissue in controls, but not in CD suggesting that the intestinal microenvironment of the colon is changed in terminal ileitis. Co-incubation with ECN tended to increase ileal LF82 adhesion, thus highlighting that careful mechanistic studies are warranted before including ECN in clinical studies. The current study demonstrates a great variability in host LF82 interactions within the group of patients with CD ileitis, thus stressing individual response patterns against LF82.