Tu1775 Spatial Mapping of the Microbiota in Ulcerative Colitis

Introduction Metagenomic sequencing technologies have offered unparalleled insights into the diversity and function of the human intestinal microbiota. Translating the large variability of communities into a precise elucidation of the dysbiotic microbiota in ulcerative colitis (UC) remains an ongoing challenge. To date there is little information pertaining to the spatial structuring of the colonic microbiota and how inflammation disrupts intestinal ecology. The aim of this study was utilize pyrosequencing as a means to elucidate the precise spatial organization of the healthy colonic microbiome and to perform a comparative analysis in ulcerative colitis (UC). Methods 4 healthy volunteers undergoing colonoscopy and 4 patients with acutely active UC undergoing proctocolectomy were sampled at four colorectal levels (caecum, transverse colon, descending colon and rectum). A fifth UC patient was sampled at the caecum and rectum only. Whole mucosal biopsies, luminal brush samples and laser capture microdissected mucus gel layer (MGL) samples were retrieved at each level, serving to represent the stratified spatial organization of the colonic microbiota. 454 barcoded pyrosequencing of the bacterial 16S rRNA gene was performed to characterize community structure. Paired histological specimens were collected to grade regional inflammation at each site. Results A total of 3,069,310 sequencing reads were generated, of which 3,041,773 were bacterial. Canonical analysis of principal components, incorporating both inflammation and categorical spatial variables revealed inter-individual variability to be the dominant variable. When compared to healthy controls, samples from patients with UC had significantly lower levels of Bacteroidaceae (13% vs 33% in luminal samples) and almost no Akkermansiaceae at any level, while harbouring significantly higher levels of Ruminococcaceae, Clostridiaceae and Bifidobacteriaceae (P