From Symbiont to Potential Carcinogenic Contributor: Examining the Pathogenic Evolution of Morganella morganii in Colorectal Cancer.

Morganella morganii (M. morganii), a member of the Enterobacteriaceae family, and a constituent of the human gut microbiota, has recently emerged as a candidate microbial contributor to the development of adenomatous polyps (AP) and promoting colorectal carcinogenesis. The present study is a narrative review compiled to evaluate the role of M. morganii in the development and progression of AP and colorectal cancer (CRC). A comprehensive literature search was conducted using Google Scholar and PubMed/Medline (2020-2026) using keywords related to the gut microbiota, M. morganii, and its impact on CRC and intestinal polyps. The ability of M. morganii to produce a specific type of genotoxin, indolimine, is a distinguishing feature of this bacterium compared to other intestinal bacteria. Because its production is independent of the pks gene cluster and the clbI and clbP genes, it exhibits a different damage pattern, namely, DNA smearing. According to reports from previous studies, strains lacking the aat gene exhibited no detectable genotoxic activity, supporting the role of aat in genotoxicity. Available data from in vitro experiments, animal models, a limited number of human observational studies, and findings from research groups suggest that M. morganii may, through the production of a highly potent genotoxin, be associated with distinct genetic damage, metabolic changes, and facilitation of polyp growth, and contribute to the development and acceleration of CRC. These findings establish a new theoretical framework in which CRC is not simply caused by gut microbiota dysbiosis, but rather reflects the activation of genotoxic bacteria and their functional interaction within the intestinal epithelial microenvironment. Nevertheless, owing to the scarcity of longitudinal human studies, it cannot yet be conclusively established whether M. morganii plays a predisposing, an initiating, or merely a consequential role in the development of CRC. Larger human studies investigating the association between M. morganii colonization and CRC development are essential for understanding the causal relationship.