Postoperative Gut Microbiota Changes after Colorectal Cancer Surgery: A Comparative Study Based on Resection Sites

Objectives: Colorectal cancer (CRC) is a major global health concern, and surgical resection remains its primary treatment. However, the impact of different surgical procedures on gut microbiota and their influence on postoperative outcomes remains unclear. This study investigated changes in the gut microbiota following three types of CRC resections: right-sided colectomy (RSC), left-sided colectomy (LSC), and low anterior resection (LAR). Methods: Fecal samples were collected from 34 patients with CRC who underwent curative resection at Fujita Health University Hospital between April 2022 and December 2023. Bacterial profiling was performed using 16S rRNA gene amplicon sequencing. The results were compared with data from 85 healthy controls. Results: Significant alterations in gut microbiota composition were observed in surgical groups compared to the healthy control (Ctrl) group. The RSC group exhibited the greatest reduction in alpha diversity, likely due to ileocecal valve loss. Beta-diversity analysis revealed distinct microbial profiles between the Ctrl group and the surgical groups, with notable alterations in key bacterial species. The RSC group exhibited significant reduction in beneficial bacteria, including Faecalibacterium prausnitzii and Bifidobacterium spp., alongside an increase in Escherichia coli, suggesting a shift toward a pro-inflammatory environment. In contrast, the LSC and LAR groups exhibited enrichment of Akkermansia muciniphila, which may promote gut barrier integrity and immune modulation. Conclusions: CRC resection induces site-specific changes in gut microbiota composition. These microbial alterations may affect postoperative inflammation, metabolism, and cancer recurrence risk. Further studies are necessary to explore microbiome-targeted strategies for improving postoperative outcomes in cases of CRC.