CHANGES IN GUT MICROBIOTA COMPOSITION CORRELATE WITH SHORT TERM CHANGES IN FACEAL CALPROTECTIN AND CRP IN PATIENTS WITH CROHN’S DISEASE

INTRODUCTION: Faecal microbiota are believed to play an important role in the pathogenesis of Crohn’s disease (CD). It is not known for certain whether gut microbiota composition (GMC) changes in response to inflammation or whether inflammation in the gut wall is a response to changes in GMC. Dynamic changes in bowel wall inflammation and short term changes in GMC have not previously been studied, but would give a clue as to the aetiological importance of GMC. AIMS & METHODS: We aimed to assess the correlation between short changes in GMC and a faecal marker of gut inflammation faecal calprotectin (FC) and CRP a marker of systemic inflammation. We conducted a blinded sham controlled cross-over study of 32 subjects assigned to IgG4 guided exclusion diets. Each subject was randomised to one month of true or sham diet followed by a one month washout period followed by a further cross-over trial diet. Stool and blood specimens were obtained at time 0, 1 month (completion of first trial diet), 2 months (completion of washout) and 3 months (end of cross-over trial diet). Taxonomic profiling was performed using 16s RNA next generation sequencing. Copy counts were made for firmicutes and bacteroidetes as a phylum; Roseburia and Bifidobacterium as a genus and Faecalibacterium prausnitzii as a species. Shannon diversity was calculated. RESULTS: 26 people fully completed the study. For each participant this provided six timepoints for comparison: timepoint 1–2, 2–3, 3–4, 1–3, 1–4 and 2–4. The relative abundance of bacteria groups were calculated. Kendall Tau correlation coefficient was used to assess correlation between change in FC and CRP to change in relative abundance of various bacteria. We found significant negative correlation with change in FC and CRP with Bifidobacterium genus and change in CRP with Roseburia genus. There were poor correlation and inconsistent changes in other species and firmicutes and bacteroidetes and Shannon diversity. CONCLUSION: Bifidobacterium relative abundance correlate closely with short term changes in FC suggesting a possible causal association. Other genera and species had poor and inconsistent correlations with short term changes in FC suggesting that they may not be causally related to short term changes in gut inflammatory activity.