Bacterial composition analysis in colorectal tissue is affected by the degree of mucus adhesion

On the colorectal epithelium, the outer mucus layer is easily removable and colonized by commensal microbiota. In contrast, the inner mucus layer is firmly attached to the epithelium and devoid of bacteria. Although the specific bacteria penetrating the inner mucus layer can contact epithelial cells and trigger cancer development, most studies do not consider the degree of mucus adhesion at sampling. Therefore, we evaluated whether bacteria adhering to tissues could be identified by removing the outer mucus layer. A total of 18 CRC patients who underwent primary tumor resection between February 2020 and January 2021 at the Fujita University Hospital were enrolled.