P0053 Microscopic colitis: analysis of microbiota changes in different segments of the colon and terminal ileum
Authors: Kiudelis V , Alzbutas G , Karaliute I , Lukosevicius R , Berneriene N , Skieceviciene J , Kupcinskas J 
Published: January 2025

Abstract

Background
Collagenous colitis (CC) and Lymphocytic colitis (LC) are forms of microscopic colitis (MC) that cause chronic watery diarrhoea, urgency, incontinence leading to significantly decreased quality of life1. The pathogenesis of MC is not fully understood; however, the leading theory suggests that MC develops as a pathological immune response to intestinal luminal antigens in genetically predisposed individuals2. Although the gut microbiota is thought to play an important part in this process, its exact role has not been fully explored to this day3. The aim of this study was to identify and characterize changes in bacterial composition of MC patients in terminal ileum and different colonic segments.

Methods
Biopsies from terminal ileum and six segments of the colon were collected during diagnostic colonoscopies. DNA extraction was performed using AllPrep DNA/RNA Micro Kit (Qiagen) following the manufacturer’s instructions. To determine bacterial composition, sequencing of the 16S rRNA variable region V3-V4 was conducted. Sequencing data were processed using DADA2, and taxonomic classification was carried out with the RDP classifier.

Results
In this study, biopsy samples from 20 active CC patients, 20 active LC patients, and 50 controls revealed distinct microbial profiles across different segments of the colon. When comparing CC patients with controls, three bacterial families showed consistent alterations throughout the entire colon, with Erysipelatoclostridiaceae and Coriobacteriaceae decreased and Pasteurellaceae increased. Additionally, 35 families had segment-specific changes, and 25 families displayed altered abundance in the terminal ileum. In contrast, LC patients exhibited a consistent increase in Erisypelotrichaceae across the entire colon, with 38 other families showing segmental changes, and 12 families displaying altered abundance in the terminal ileum. The comparison between LC and CC highlighted a significantly different bacterial profile, with LC showing lower abundance across many families, particularly in the terminal ileum. This segmental dysbiosis pattern, more pronounced in the proximal colon, may contribute to the distinctive pathophysiology in microscopic colitis subtypes.

Conclusion
This study showed significant differences in bacterial composition between CC, LC and controls in the terminal ileum and colon. Bacterial alterations were not consistent throughout the entire colon but varied between different colonic segments.

References
1. Verhaegh BPM, Münch A, Guagnozzi D, et al. Course of Disease in Patients with Microscopic Colitis: A European Prospective Incident Cohort Study. J Crohns Colitis. 2021;15(7):1174-1183.
2. Miehlke S, Guagnozzi D, Zabana Y, et al. European guidelines on microscopic colitis: United European Gastroenterology (UEG) and European Microscopic Colitis Group (EMCG) statements and recommendations. United European Gastroenterol J. Published online 2020.
3. Burke KE, D’Amato M, Ng SC, Pardi DS, Ludvigsson JF, Khalili H. Microscopic colitis. Nat Rev Dis Primers. 2021;7(1).