Perioperative microbiota at the colorectal anastomosis: local host-microbe interactions in healing and leak.

Anastomotic leak remains a major complication after colorectal resection, but established clinical and technical risk factors do not fully explain why some repairs fail during early healing. This review treats perioperative microbiota as part of a local host-microbe wound environment at the colorectal anastomosis rather than as a broad gut microbiome signal. Literature was identified through PubMed and Web of Science searches covering 1 January 2010-6 July 2026, using terms combining colorectal anastomosis, anastomotic leak, microbiota, microbiome, and host-microbe interactions. Evidence was tiered by directness to the anastomotic wound, distinguishing stool-based proxy signals from mucosal, tissue-adjacent, and functional measurements. Stool and broader luminal profiles provide indirect signals for suture-line events unless paired with site-aware sampling. Mucosal, mucus, and tissue-adjacent studies move closer to the repair site but remain mostly exploratory and associative. Animal and in vitro work supports plausible mechanisms, including collagenase activity, biofilm-like persistence, metabolite signaling, inflammatory modulation, and extracellular matrix injury, but does not establish human clinical causality. Current evidence justifies better perioperative sampling, function-aware microbial analysis, and integration with conventional leak-risk factors; it does not justify routine microbiome-guided risk stratification or leak-prevention interventions. The most useful next step is longitudinal, site-aware human work anchored to standardized leak outcomes and surgical context.