Short- and long-term dynamics of gut microbiota, highlighting Fusobacterium nucleatum , Parvimonas micra , and Peptostreptococcus stomatis after colorectal cancer resection: prospective cohort study

BACKGROUND: Colorectal cancer is associated with gut microbiota alterations, including enrichment of colorectal cancer-associated bacteria such as Fusobacterium nucleatum, Parvimonas micra, and Peptostreptococcus stomatis. However, the impact of curative resection on their postoperative dynamics remains unclear. METHODS: Faecal samples were collected from patients with colorectal cancer and controls. Samples were collected before surgery and at 1 week, 1 month, and 6 months after surgery. Microbial diversity was evaluated using 16S ribosomal RNA sequencing, and F. nucleatum, P. micra, and P. stomatis were quantified by quantitative polymerase chain reaction. RESULTS: A total of 83 faecal samples were collected from 28 patients with colorectal cancer and 16 healthy controls. Alpha diversity decreased at 1 week and recovered by 1 month. Unweighted unique fraction metric suggested recovery of community membership by 6 months, whereas Bray-Curtis and weighted unique fraction metric remained altered, indicating persistent community reorganization. At the class level, Negativicutes and Clostridia decreased at 1 week and gradually recovered, whereas Bacilli showed a transient increase. In contrast, F. nucleatum, P. micra, and P. stomatis declined significantly after surgery and remained suppressed at 6 months. Patients who developed recurrence had higher preoperative P. micra and P. stomatis levels, though differences were not observed after surgery. CONCLUSION: Colorectal cancer resection induces an acute postoperative disruption of the gut microbiota, followed by recovery of overall diversity and major taxonomic features, but stabilization in a state that does not fully recapitulate the preoperative microbiota. Colorectal cancer-associated bacteria (F. nucleatum, P. micra, and P. stomatis) remained persistently reduced after surgery, highlighting their dependence on the tumour microenvironment. Monitoring these bacteria in faecal samples may offer a non-invasive means to assess microbiota recovery and potential recurrence risk.