Increasing evidence highlights the critical role of intestinal microbiota, particularly oncogenic microbes, in the initiation and progression of colorectal cancer (CRC). This PhD project aims to elucidate oncogenic epithelial-microbiota interactions by isolating tumor-adherent and intratumoral microorganisms from surgically resected CRC tissues. These isolated bacteria and fungi will be screened in vitro for genotoxic potential using CRC cell lines and advanced intestinal organoid cultures, including innovative intra-organoid microbial injections and expression profiling analyses. Selected oncogenic bacteria will then be validated in vivo for their tumor-promoting capabilities using two transgenic mouse models of microbial-driven CRC, including gnotobiotic experiments where germ-free transgenic mice are colonized with candidate oncobacteria. Molecular mechanisms underlying these interactions will be explored using advanced cellular and molecular assays, complemented by metabolomics analyses. Finally, using an advanced metastatic CRC model involving intracolonic injection of tumor organoids, we will examine whether specific CRC-associated bacteria influence metastatic progression. This research is pivotal in uncovering microbiota-driven mechanisms in CRC, potentially identifying novel microbial targets and therapeutic strategies for CRC prevention and treatment.