(A-26) Mucus clearance alterations induce biofilm formation in the gut

Colorectal cancer (CRC) is the third most frequent cancer worldwide, and despite being treatable through surgery, it is the second most deadly. CRC biopsies indicate that the disease correlates positively with an altered gut microbiota that colonizes the intestinal mucus, forming polymicrobial communities or biofilms. When tested in mouse models, these biofilms are potent tumor inducers; however, the mechanisms by which they form in the gut remain unknown. This lack of understanding derives primarily from the lack of experimental platforms that accurately mimic the human colonic mucus, the complexity of polymicrobial communities, and the limited experimental and analytical tools to interrogate mucosal biofilms in vivo and ex vivo. Because of the mucus's high renewal rate in the proximal colon, we have hypothesized that microorganisms with biofilm formation capabilities had to balance mucus degradation and exfoliation to thrive at the mucosal interface. We developed an ex vivo mucus system for studying gut biofilms by harvesting intact mucus from goblet cells. We found that this mucus mimicked the mechanical spectrum of human CRC biopsies. We established a new experimental method to investigate mucosal biofilms based on their capacity to use the mucus as a scaffold, as determined by their structural properties via oscillatory rheology. We evaluated several CRC-associated species for their ability to form biofilms on mucus, including Bacteroides fragilis, Fusobacterium nucleatum, and Enterococcus faecalis. Among those, E. faecalis preserved the structural integrity of mucus and formed viscoelastic biofilms that were stable for up to five days in anaerobic conditions. Furthermore, the viscoelastic properties of E. Faecalis's biofilms remained consistent throughout this period, suggesting that biofilm formation was not reliant on the production of extracellular polymer substances. Additionally, E. faecalis's biofilms were insensitive to DNase treatment and glucose concentration in the culture media. This study is the first to show a potential mechanism for biofilm formation in the gut. The mechanistic understanding of biofilm formation will allow the design of more effective treatment therapies against CRC and to detect the disease before symptoms develop, ultimately improving health outcomes.