Microbiological aspects of Crohn's disease

Abstract

Inflammatory Bowel Disease (IBD) is a chronic inflammatory process that affects any part of the gastrointestinal tract in Crohn's disease (CD), or the large intestine in ulcerative colitis. It is thought to result from an ongoing immune response against gut bacteria in genetically susceptible individuals. Putative pathogens, an imbalance of 'good' and 'bad' bacteria, and excessive bacterial translocation have all been implicated. The aim of these studies was to investigate the role of gut bacteria with a specific focus on the lymph node, as a means of identifying microbial triggers of CD. The microbiological composition of lymph nodes and two mucosal sites from surgically resected specimens was investigated. Bacterial DNA was detected in lymph nodes of 20/58 patients (8 CD, 2 other-IBD, 10 non-IBD). The bacterial content of all samples from an individual patient was similar, as determined by high-throughput sequencing. An imbalance in bacterial phyla was common in all patient groups, but microbial diversity of CD samples was lower than non-IBD. No single bacterial species was found more commonly in patients with CD than those without IBD: Campylobacter was detected in 3 CD and 1 non-IBD patient; Helicobacter in 1 CD and 1 non-IBD patient; and Yersinia in 1 other-IBD patient.

Mycobacteria and Listeria were not detected in any patient. The similarity between mucosal and lymph node specimens suggests that colonoscopic biopsies are suitable for seeking bacterial triggers of CD. Analysis of the micobome in CD studies is frequently performed using biopsies obtained during colonoscopy, a procedure requiring a bowel cleansing preparation. Stool samples were collected from 15 subjects undergoing colonoscopy; two samples were collected pre-, and three post-colonoscopy. Stool samples taken 3-6 months apart from 5 healthy controls were also examined. Variation in the microbial composition between pre- and post-colonoscopy samples from the same patient was no greater than the variation observed between the two pre-colonoscopy samples and control samples, indicating colonoscopy does not have a significant impact. Adherent-invasive Escherichia coli (AIEC) have been implicated in ileal CD, but the factors that contribute to their potential virulence are unknown. We noted that patients with ileal CD had a greater proportion of E. coli reads in lymph nodes than other patients with CD (P=0.0475). E. coli were cultured from lymph nodes and mucosa and 20, 12, and 10 strains from CD, other-IBD, and non-IBD tissues, respectively, were examined for the distribution of a plasmid harboured by the archetypal AIEC strain, LF82, and another potential virulence factor, long polar fimbriae (lpfA). The LF82-like plasmid was detected in E. coli from 1 non-IBD patient, and the LF82-lpfA variant in 14%, and Shigella-lpfA variant in 36% of strains. However, both lpfA variants were distributed similarly across all patient groups. It is unlikely the LF82-like plasmid, LF82-lpfA, or Shigella-lpfA variants are essential for AIEC pathogenicity. Mechanisms that allow E. coli to remain viable in lymph nodes of patients with CD should be explored by comparing the genomes of lymph node isolates. These studies suggest that CD is a heterogeneous condition of multifactorial aetiology. -- provided by Candidate. Show more