P868 Microbial expression in biopsies from ulcerative colitis at the time of diagnosis: bacterial activity is unrelated to abundancy

Abstract

Background: The composition of the intestinal microbiota is considered to play a role in the development of ulcerative colitis (UC). The characterisation of bacterial DNA does not separate viable from dormant or dead bacterial strains. Assessment of bacterial activity could be more relevant to the study of pathogenetic mechanisms. The purpose of the present study was to compare the activity of mucosal microbiota in normal and inflamed tissue of newly diagnosed, treatment-naive UC patients, and to see if bacterial activity relates to abundancy (if the most active members are the most abundant). Methods: Colonic biopsies from inflamed and histologically noninflamed tissue of 44 UC patients (10 proctitis, 14 left-sided colitis, 20 pancolitis) and from 35 symptomatic subjects without inflammatory bowel disease (non-IBD controls) were collected. The mucosal microbiota was assessed for abundancy (DNA) and activity (RNA) within the same biopsy. 16S rRNA amplicon sequencing was performed on both gene product and DNA. Data were analysed by Mothur and R. Results: The inflamed and non-inflamed mucosal microbiota in UC patients revealed differences among abundant and active members. Increases of the phylum Proteobacteria and the family Enterobacteriaceae were found in the abundant microbiota, but not among the active microbiota, suggesting a less prominent function or pathophysiological role in the inflamed tissue. Functional assessment revealed a decrease of the phyla Proteobacteria and Actinobacteria, as well as the families Alcaligenaceae and Bifidobacteriales (Table 1). (Table presented) Biopsies from non-inflamed mucosa in UC and non-IBD patients showed similarities in abundant and active members. Increases in active Enterobacteriaceae and the Firmicutes family Peptostreptococcaceae in UC as compared with non-IBD patients indicate important contributions to the UC microbiota. Conclusions: The abundant and active members of the UC mucosaassociated microbiota deviated between tissue inflammation status, and the most abundant members are not the most active ones. Studies on gut microbiota host interactions should aim to detect the active members which most likely have more influence on the host reactions compared with those with highest abundancy as detected on the DNA level.