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* = Presenting author

P700. Evaluation of location-specific, tissue-associated microbiota in the ileal pouch, terminal ileum and colon in inflammatory bowel disease (IBD)

A. Tyler1, C. Huttenhower2, D. Gevers3, M. Silverberg1, 1Mount Sinai Hospital, Toronto, Canada, 2Harvard University, School of Public Health, Boston, United States, 3The Broad Institute of MIT and Harvard, Boston, United States

Background

The microbiome has been evaluated separately in conventional IBD and post-ileal pouch-anal anastomosis (IPAA), however, a comparison of the microflora between these groups has not been conducted. The aim of this study was to compare and contrast the microbial profile of colonic and ileal tissue with that of pouch and afferent limb tissue.

Methods

Subjects with Crohn's disease (CD), ulcerative colitis (UC) (with and without a pouch), familial adenomatous polyposis (FAP) (with a pouch) and healthy controls (HC) were recruited from Mount Sinai Hospital, Toronto. Biopsies were taken from the pouch and afferent limb of patients with pouches, and from the sigmoid and terminal ileum (TI) of those without, during standard of care endoscopy. Demographic, clinical and endoscopic data was recorded at the time of procedure. Microbial DNA was extracted and the V4-V5 hypervariable region of the 16S rRNA gene was sequenced using the Illumina MiSeq platform. Paired end reads were quality trimmed, assembled into OTUs with 97% sequence identity and assigned to taxonomy using QIIME. Raw counts were converted to abundance, and comparisons between sampling locations were conducted using non-parametric statistics with false discovery rate (FDR) correction for multiple testing in R and LEfSe.

Results

In total 628 samples from 373 individuals were included in the analysis (HC = 44, CD = 41, UC = 42, FAP = 1, UCIPAA = 213 and FAPIPAA = 32). 108 genera meeting inclusion criteria were detected. No differences between the pouch and the afferent limb were detected yet several organisms were differentially abundant between sigmoid and TI samples. Numerous genus-level alterations were observed between pouches and both sigmoid and TI samples (pFDR < 0.05). Shifts in the microbiota between patients with and without pouches included an increase in members of Proteobacteria in pouches and Clostridia and Bacteroidetes in colonic tissue. Frequencies of several genera in the pouch were similar to those in the TI, while others resembled those in the sigmoid. Furthermore, organisms which were previously implicated in pouchitis or non-surgical IBD were detected at differential levels between pouch and non-surgical samples.

Conclusion

Differences in the microbial composition of pouch and non-surgical IBD tissue are apparent and may correspond to adaptive changes in the ileal pouch following surgery. Such differences may be important for better understanding pathogenesis and for clinical management.