# CAG Student Prize Paper – A3 ESCHERICHIA COLI PATHOBIONTS ISOLATED FROM ULCERATIVE COLITIS PATIENTS HARBOUR NUMEROUS PROTEINS THAT DEGRADE HUMAN COLONIC MUCUS

## TL;DR

This study shows that certain E. coli strains from ulcerative colitis patients can break down human colon mucus, potentially contributing to the disease's progression.

## Contribution

The study identifies multiple mucinase genes in E. coli isolates from UC patients and demonstrates their ability to degrade human colonic mucus.

## Key findings

- E. coli isolates from UC patients degrade human colonic mucus, with UC-derived mucus being more susceptible.
- Multiple mucinase genes (sslE, vat, pic) are commonly present in UC-associated E. coli strains.
- Some E. coli isolates can degrade both non-IBD and UC-derived mucus, suggesting a role in disease severity.

## Abstract

The etiology of ulcerative colitis (UC) remains elusive, with current evidence suggesting weakened mucosal barriers allow noxious luminal stimuli to escape the colonic lumen and trigger inflammation. Escherichia coli pathobionts, particularly of phylogroup B2, have been associated with active UC, however their role in disease is unclear. We previously showed that UC-associated E. coli p19A can penetrate the mucus barrier of UC air-liquid interface (ALI) monolayers. We hypothesize that E. coli pathobionts carried by UC patients degrade their colonic mucosal barriers, thereby contributing to the onset, severity, and chronicity of UC.

Using healthy and UC patient biopsy-derived colonic organoids and an ALI monolayer model, we investigated the ability of p19A as well as other E. coli isolates from UC patients to degrade human colonic mucus.

ALI monolayers from non-IBD and UC patients were grown, with apical mucus collected, then incubated with secreted proteins from E. coli p19A. Degraded mucus was detected by protein gel and MUC2 western blot. To expand our understanding of UC-isolated E. coli mucus degradation, we analyzed the phylogeny and the mucinases present in the genomes of 92 E. coli strains isolated from UC patients as well as assessed a subset of isolates ability to degrade human mucus.

We show that p19A degrades human ALI monolayer-derived mucus, with UC ALI-mucus more readily degraded. We identified the known mucinases Pic and Vat in p19A and found a ΔpicΔvat mutant strain retained the ability to degrade mucus, suggesting another secreted protein(s) has mucinase activity. Phylogenetic analysis of 92 clinical E. coli isolates revealed 49% are clustered with IBD pathobionts like p19A. sslE, vat, and pic were the most common mucinase genes, present in 54%, 45%, and 30% of the E. coli isolates, respectively. In addition, nine E. coli isolates derived from four UC patients each harboured three known mucinase genes (pic, vat, and sslE). Mucus degradation assays using secreted proteins from a selected subset of ten phylogenetically distinct isolates (nine from phylogroup B2) revealed that five isolates could degrade both non-IBD and UC-ALI derived mucus, while an additional two isolates could degrade only UC-ALI derived mucus.

UC patients harbor E. coli strains that contain numerous mucinase genes, many of which can degrade human ALI monolayer-derived mucus, with UC-ALI mucus more easily degraded. Therefore, specific E. coli strains may act as pathobionts, weakening the mucosal barrier in UC patients, thereby contributing to the onset, severity, and/or chronicity of UC.

CCC, CIHRWeston Family Foundation (Canadian National Organoid Network)