Intratumoral Bacterial Profiles, Bacterial Co-Detection Patterns, and Molecular Alterations in Colorectal Cancer and...

Intratumoral microbiota may contribute to colorectal cancer (CRC), but their relationships with bacterial co-occurrence, relative bacterial loads, and molecular alterations remain incompletely understood. This study characterized intratumoral bacterial profiles in CRC and colorectal polyps and examined their clinicopathological and molecular associations. A cross-sectional study included 149 patients with CRC and 109 patients with benign colorectal polyps. F. nucleatum, ETBF, A. muciniphila, and eae⁺E. coli were detected in formalin-fixed, paraffin-embedded tissues using multiplex real-time PCR, with relative bacterial loads quantified using the 2^-ΔCt method. KRAS and BRAF V600E mutations and HSP110ΔE9 transcripts were assessed by real-time PCR/RT-qPCR. After multivariable adjustment for age, sex, tumor location, and the other bacterial species, ETBF and eae⁺E. coli were independently associated with CRC (adjusted ORs, 4.69 and 6.26, respectively; both p < 0.001). Relative loads of all four bacterial species were higher in CRC than in polyps (p < 0.001 for all comparisons). ETBF + eae⁺E. coli showed the strongest dual-species association with CRC (adjusted OR, 10.64; 95% CI, 4.49-25.24), while F. nucleatum + A. muciniphila + eae⁺E. coli showed the strongest triple-species association (adjusted OR, 21.56; 95% CI, 5.02-92.60). Increasing numbers of detected bacterial species were positively associated with CRC (p for trend < 0.001). CRC was characterized by higher relative bacterial loads and more interconnected bacterial co-colonization patterns than colorectal polyps. These findings support a community-level association between intratumoral bacterial profiles and CRC and warrant validation in larger multicenter longitudinal studies.