The Role of Surgical and Perioperative Factors in Shaping Gut Microbiome Recovery After Colorectal Surgery

The gut microbiome is essential for gut health, immune regulation, and metabolism, but pathogenic bacteria like Enterococcus and Streptococcus can disrupt these processes, increasing infection risk after colorectal surgery. Prior studies show that intravenous antibiotics and surgical bowel preparation (SBP, including mechanical preparation with oral antibiotics) significantly disrupt the gut microbiota, potentially delaying postoperative recovery. However, the effects of surgical indication (e.g., diagnosis) and operation type on gut microbiome composition and function remain unclear. This study examines how SBP, resectional and non-resectional surgery, and underlying diagnoses shape the postoperative gut microbiome and microbial recovery. Methods: Fecal samples were collected from patients undergoing colonoscopy (n = 30), non-resectional (ventral mesh rectopexy, transanal surgery; n = 25), or resectional surgery with primary anastomosis (n = 26) at baseline, intraoperatively, and on postoperative days (POD) 10, 30, and 180. Microbial diversity was assessed through 16S rRNA sequencing, and short-chain fatty acid (SCFA) levels were measured to evaluate functional changes. Results: Alpha diversity (Shannon indices) decreased across all groups, recovering by POD10 in colonoscopy patients and by POD180 in non-resectional and resectional cohorts. Beta diversity (community composition) also returned to baseline by POD10 in colonoscopy patients and POD180 in non-resectional patients, but the resectional cohort did not fully recover (p < 0.001). Both surgical cohorts showed substantial losses of commensal bacteria through POD30, with notable increases in Streptococcus in resectional patients (p < 0.0001) and Enterococcus in both surgical cohorts (p < 0.0001). Functionally, only the resectional cohort experienced significant reductions in SCFA levels (p < 0.015) relative to baseline levels. Diagnosis minimally influenced long-term microbiota recovery, although cancer patients tended to have more stable microbiomes compared to patients with diverticulitis. Conclusions: These findings indicate that perioperative factors, especially surgical resection and SBP, significantly impact gut microbial recovery, with pathogenic bacteria persisting up to 6 months post-surgery.