Margarita Poza

Oral and intestinal samples from a cohort of 93 colorectal cancer (CRC) patients and 30 healthy controls (non‐CRC) were collected for microbiome analysis. Saliva (28 non‐CRC and 94 CRC), feces (30 non‐CRC and 97 CRC), subgingival fluid (20 CRC), and tumor tissue samples (20 CRC) were used for 16S metabarcoding and/or RNA sequencing (RNAseq) approaches. A differential analysis of the abundance, performed with the ANCOM‐BC package, adjusting the P ‐values by the Holm‐Bonferroni method, revealed that Parvimonas was significantly over‐represented in feces from CRC patients ( P ‐value < 0.001) compared to healthy controls. A total of 11 Parvimonas micra isolates were obtained from the oral cavity and adenocarcinoma of CRC patients. Genome analysis identified a pair of isolates from the same patient that shared 99.2% identity, demonstrating that P. micra can translocate from the subgingival cavity to the gut. The data suggest that P. micra could migrate in a synergistic consortium with other periodontal bacteria. Metatranscriptomics confirmed that oral bacteria were more active in tumor than in non‐neoplastic tissues. We suggest that P. micra could be considered as a CRC biomarker detected in non‐invasive samples such as feces.