| Inflammatory bowel disease (IBD) etiology likely involves several factors including gut bacteria, immunological responses and genetic characteristics. Results from investigations with animal models and human subjects suggest that resident microbiota play an important role in the IBD. To better understand IBD etiology, in this dissertation, I attempted to identify associations between bacterial rRNA gene populations and disease activity and disease type.;Associations between several bacteria including Lachnospiraceae and Clostridium ramosum and colitis disease activity were identified in IL-10-/- mice. These associations, along with other results from the literature, led to the development of a model of IBD etiology that involved intracellular infections as a key element. Subsequent investigations of IL-10-/- mice with different genotypes provided several results supporting this new model. Investigations of human samples endeavored to identify bacteria associated with IBD disease type. A Ruminococcus phylotype, which is a member of Lachnospiraceae, was significantly reduced in IBD subjects. A Faecalibacterium phylotype was found to be reduced in Crohn's disease but not in ulcerative colitis. This study also identified a new type of bacteria that exhibits differential associations with IBD, which is the mucin-degrading bacteria Akkermansia muciniphila. |
