Muribaculum as a microbial contributor of rifaximin-induced mucosal protection during chemotherapy.

Chemotherapy-induced intestinal mucositis is a frequent and dose-limiting toxicity that compromises cancer treatment outcomes and lacks effective targeted interventions. Here, we investigate the mechanisms by which the nonabsorbable antibiotic rifaximin mitigates chemotherapy-induced intestinal injury, focusing on microbiota-mediated preservation of epithelial barrier integrity. In a murine model of 5-fluorouracil (5-FU)-induced intestinal injury, rifaximin pretreatment reduced mucosal inflammation and tissue damage, preserved epithelial and mucus barrier integrity, and limited systemic endotoxemia. Importantly, rifaximin did not impair the antitumor efficacy of 5-FU in ApcMin/+C3arKO mice. To assess translational relevance, we employed a human intestinal ex vivo organ culture system (EVOC) and found that rifaximin preserved mucosal architecture, mucus balance, and tight junction integrity following inflammatory challenge. Microbiome profiling revealed that rifaximin reshaped the intestinal microbial community, preventing the depletion of health-associated taxa, including Muribaculum and Parasutterella. Functional experiments demonstrated that Muribaculum intestinale supplementation alone attenuated 5-FU-induced injury, reproducing key protective features of rifaximin treatment. Together, these findings identify Muribaculum as a microbial contributor to rifaximin's protective effects, supporting its potential role as a safe adjunctive strategy to improve gastrointestinal tolerability of cancer treatment.