The perioperative microbiome of patients undergoing rectal cancer surgery: A pilot study

Abstract Aim The gut microbiome plays a crucial role in health and disease, and its involvement in postoperative complications like anastomotic leakage (AL) is of growing interest. Despite substantial preclinical evidence linking microbiome alterations to surgical outcomes, human studies are scarce, particularly those exploring the perioperative dynamics of the gut microbiome beyond a single time point. This descriptive, hypothesis‐generating pilot study aims to elucidate the perioperative changes in the faecal microbiome of patients undergoing rectal cancer surgery. Method Seventeen patients from Amsterdam University Medical Centers participated in the IMARI‐study and the IntAct‐trial between April 2020 and April 2022. All patients in these studies underwent rectal resection for malignancy with a primary anastomosis, with or without a diverting ileostomy. Samples collected included preoperative stool, intraoperative anastomotic colonic tissue and swab and postoperative stool. Bacterial DNA was extracted and analysed using 16S rRNA gene sequencing. Results An increase in Enterococcus and Streptococcus was observed postoperatively compared to preoperative and intraoperative samples. Postoperative samples showed a significant decrease in alpha diversity compared to preoperative and intraoperative samples. Beta diversity analysis revealed distinct clustering of postoperative stool and ileostomy samples. Preoperative oral antibiotics significantly altered the intraoperative microbiome composition and reduced postoperative alpha diversity. Conclusion This pilot study reveals significant perioperative shifts in the gut microbiome of rectal cancer patients. These findings underscore the importance of considering microbiome dynamics perioperatively when designing and interpreting studies that correlate the microbiome with clinical outcomes. However, the conclusions should be viewed as preliminary and require confirmation in larger studies, including causal relation, to postoperative outcomes.