The intestinal microbiome impact on anastomotic healing in colorectal surgery - a prospective clinical pilot study

Abstract Introduction AL is one of the most severe complications after bowel resection. The incidence remains between 4-10% after colorectal surgery despite advancements in surgery and perioperative care. The intestinal microbiome’s regulation of host health and its impact on anastomotic healing are increasingly recognized, but the underlying mechanisms and strategies for clinical implementation remain poorly understood. In a prospective clinical study, we aim to identify the optimal timing of intestinal microbiome faecal sampling and to compare microbiomic differences in patients with anastomotic leak (AL) compared to no leak. Method Faecal samples were collected at three time points from patients with colorectal cancer undergoing intestinal resection and anastomosis, pre-operative (stool), operative (swab) and postoperative (stool). Shotgun sequencing was performed using MGI whole-genome sequencing technology. Result Of 42 patients, 6 suffered from AL. The operative swab sample had the highest level of ´high quality non host DNA´. The taxonomic overview at family level was similar between all time points. Alpha-diversity and overall microbiome community composition was more similar between pre-operative and operative samples compared to post-operative. No differences in microbiome composition or diversity were noticed between patients with or without AL. Bacterial propionate-synthesis was identified as a significant protective factor against AL. Discussion The intraoperative swab sample was the most feasible and informative, yielding the highest non-host DNA. Our findings highlight the value of functional microbiome profiling—especially short-chain fatty acid synthesis—as a potentially more relevant predictor of anastomotic healing than taxonomic composition alone. Future studies are planned to further elucidate these findings.