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

Enterococcus and Streptococcus abundance increased postoperatively compared to preoperative and intraoperative samples.

• 17 patients from Amsterdam University Medical Centers participated in the IMARI-study and the IntAct-trial between April 2020 and April 2022.
• All patients underwent rectal resection for malignancy with a primary anastomosis, with or without a diverting ileostomy.
• Bacterial DNA was extracted and analysed using 16S rRNA gene sequencing.
• The increase in Enterococcus and Streptococcus was observed in postoperative stool samples compared to both preoperative stool and intraoperative samples.

Alpha diversity of the gut microbiome significantly decreased postoperatively compared to preoperative and intraoperative samples.

• Postoperative stool samples showed a significant decrease in alpha diversity.
• The decrease was observed when comparing postoperative samples to both preoperative stool and intraoperative anastomotic tissue and swab samples.
• Samples were collected at three perioperative time points: preoperative stool, intraoperative anastomotic colonic tissue and swab, and postoperative stool.
• Analysis was performed using 16S rRNA gene sequencing on 17 patients.

Beta diversity analysis revealed distinct clustering of postoperative stool and ileostomy samples compared to other sample types.

• Beta diversity analysis was conducted across preoperative, intraoperative, and postoperative sample types.
• Postoperative stool samples and ileostomy samples formed distinct clusters separate from preoperative and intraoperative samples.
• This finding suggests that postoperative microbial community composition differs substantially from both preoperative and intraoperative compositions.
• The study included patients both with and without a diverting ileostomy, allowing comparison between these groups.

Preoperative oral antibiotics significantly altered the intraoperative microbiome composition and reduced postoperative alpha diversity.

• Oral antibiotic administration prior to surgery was associated with significant changes to the microbiome measured intraoperatively.
• Preoperative oral antibiotics also reduced postoperative alpha diversity compared to patients not receiving oral antibiotics.
• This finding highlights oral antibiotics as a key perioperative factor influencing microbiome dynamics.
• The study was conducted in a cohort of 17 rectal cancer patients, and these findings are considered preliminary.

This study identified perioperative microbiome dynamics as an important methodological consideration for studies correlating gut microbiome with postoperative outcomes such as anastomotic leakage.

• The study is described as a 'descriptive, hypothesis-generating pilot study' aimed at elucidating perioperative changes in the faecal microbiome.
• The authors note that 'human studies are scarce, particularly those exploring the perioperative dynamics of the gut microbiome beyond a single time point.'
• The authors caution that 'conclusions should be viewed as preliminary and require confirmation in larger studies, including causal relation, to postoperative outcomes.'
• Multiple sample types were collected (preoperative stool, intraoperative anastomotic colonic tissue, intraoperative swab, and postoperative stool) to capture dynamics across the perioperative period.