Dominant Genotypes in Mucosa-Associated Escherichia Coli Strains from Pediatric Patients with Inflammatory Bowel Disease

Escherichia coli (E. coli), a predominant facultative anaerobe of the human colonic flora, has been thought to participate in the pathogenesis of inflammatory bowel disease (IBD). Increased numbers of mucosa-associated E. coli have been observed in adult IBD patients; furthermore, some E. coli strains from Crohn's disease (CD) patients have been shown to adhere to intestinal epithelial cells and invade them, as well as to replicate extensively into macrophages. It has also been suggested that some E. coli genotypes are more likely than others to be associated with CD in adults. There are no studies on the molecular characterization of mucosa-associated bacteria in children with pediatric IBD. Aims: children with IBD were investigated in order to characterize mucosa-associated E. coli strains and to assess if a particular subset of E. coli strains could be associated with IBD in these subjects. Methods and subjects: we analyzed genomic profile, phylogenetic grouping, virulence-gene carriage, different biochemical and enzymatic properties, and adhesive/invasive abilities of 60 E. coli strains isolated from mucosal biopsies of pediatric patients affected by CD (12 cases), ulcerative colitis (UC) (7 cases), and from those of 19 children with functional intestinal disorders who served as controls. Median (and ranges) age (years) was 14.0 (12-17), 10.0 (8-13), 12.7 84-16), respectively. Patients underwent ileo-colonoscopy as a step of their diagnostic approach after parental written consensus. The study was approved by the ethical committee of the Faculty. Results: in E. coli strains deriving from IBD patients and from controls no noteworthy differences were found in the distribution of phylogroups, in the adhesive properties as well as in the occurrence of virulence-related genes . However, the genetic profile examination revealed two large clusters of genetically linked E. coli strains from IBD patients: in the first cluster were grouped 92% of E. coli strains isolated from CD patients, distributed between two sub-clusters; in the second cluster 78% of strains isolated from UC and 77% from controls, distributed between two sub-clusters, respectively. Conclusions: in children with IBD, whereas phenotypic characterization failed to identify peculiar pathogenetic strains, genomic analysis was able to define a close genetic relatedness among E. coli strains associated with CD and UC gut mucosa.