Comparative Analysis Of Host-Bacterial Interactions In The Gastrointestinal Tract
Technological advances in culture-independent methods using high throughput DNA sequencing have revolutionized our understanding of gastrointestinal (GI) microbiology. Our ability to now characterize the intestinal microbiome (IM) in incredible depth affords insight into the dynamic interrelationships of bacteria with the other pathomechanisms underlying inflammatory bowel diseases (IBD), i.e. genetics, immune dysregulation, and environmental triggers. This work explores these complex interactions in a murine model of Crohn‟s Disease (CD) and canine IBD. In C57BL/6 mice, we reveal that T. gondii and indomethacin-induced ileitis induce a microbial shift termed „dysbiosis,‟ comprising reduced microbial diversity and a global shift from >95% Gram+ (Firmicutes) to >95% Gramspecies (Proteobacteria), which recapitulates the IM of ileal CD. Gramproliferation also appears permissive to intramucosal invasion by the emerging pathogen, Adherent Invasive E. coli (AIEC). By manipulating genetic susceptibility to CD (NOD2-/-) and severity of ileitis (CCR2-/- and anti-TNF[alpha]mAb), we show that dysbiosis is the common end-point of acute ileitis, driven by inflammation rather than genotype or trigger. We postulate that failure to reverse dysbiosis stimulates chronic microbial-driven inflammation in CD. Unlike other GI pathology, e.g. Helicobacter-induced gastric ulceration, the evidence for a specific pathogen in CD is controversial, though growing evidence implicates AIEC. Pathogenicity of AIEC is highlighted by their firm association with Granulomatous colitis (GC) of Boxer dogs. We strengthen the evidence for a direct causal relationship by documenting intramucosally invasive E. coli in 17 GC cases. Further, GC remission correlates with E. coli sensitivity to enrofloxacin, whereas antimicrobial-resistant E. coli are associated with poor outcome. By genome-wide association study, we uncover for the first time parallels between GC and the colitis of human Chronic Granulomatous Disease (CGD), pointing to a potential role for AIEC in CGD pathogenesis. In idiopathic canine IBD, we demonstrate dysbiosis characterized by Bacteroidales depletion and increased Gram- diversity. We highlight potentially distinguishing features of the IM in IBD that warrant further evaluation as potential predictors of treatment response. In protein-losing enteropathy of Yorkshire Terriers, we document a severe, often fatal IBD, associated with sterile, multifocal crypt abscesses. Since we uncover no evidence of a bacterial etiology, we conclude that a familial morphogenetic disorder may be responsible.
Dysbiosis; inflammatory bowel disease
Simpson, Kenneth William
Denkers, Eric Young; McDonough, Sean P
Ph.D. of Veterinary Medicine
Doctor of Philosophy
dissertation or thesis