P854 Quantitative microbiome profiling changes the described dysbiotic state in inflammatory bowel disease

Abstract

Background: Gut microbiota play a crucial role in inflammatory bowel disease (IBD). The usage of culture-independent techniques lead to the identification of dysbiosis in IBD, but generate only relative microbiome profiles (RMP) with no ability to provide information on the extent or directionality of changes in taxa abundances. Quantitative microbiome profiling (QMP) combines microbiome sequencing with flow cytometric counting of microbial cells to quantitatively assess microbiota variation (Vandeputte et al., 2017). We aimed to investigate the differences in microbial load in patients with active Crohn's disease (CD). We compared the distribution of the different enterotypes and hypothesised that microbial load may be associated with the inflammatory status in IBD. Methods: Fecal samples of 69 CD patients with endoscopically active disease were collected prior to biological therapy. Fecal samples of 66 healthy controls (HC) from the Flemish Gut Flora Project (FGFP) were used as comparison. Microbiota phylogenetic profiling was conducted by using 16S rRNA gene amplicon sequencing, and microbial loads of frozen fecal samples were measured using flow cytometry. These cell counts were used to transform the sequencing data into an absolute microbiome abundance matrix that allowed QMP by modifying sequencing depth rarefying procedures and generated QMP expressed as number of cells per gram faces. Results: Our flow cytometric analysis data confirm a significant lower microbial load (Wilcoxon r =-0.49; p < 0.001) in active CD, up to a hundred-fold lower, compared with HC (Figure 1). Enterotypes distribution varies between the active CD and HC. Notably, 10.6% of the FGFP samples were typed as Bacteroides2, compared with a much higher prevalence of 88.2 % in our patients with active CD. Furthermore, we compared the microbial load between clinical responders (defined as HBI score of