the validation of experiment

Bowel preparation with polyethylene glycol electrolyte solution (PEG-ELS) is indispensable for gastrointestinal endoscopy and related procedures. However, it disrupts gut microbial homeostasis and increases host vulnerability to ensuing infection. Here we optimized a synbiotic intervention consisting of fructooligosaccharides (FOS) and Clostridium butyricum (C. butyricum) to improve post-cleansing microbiome resilience and mucosal defense. We evaluated its efficacy and longitudinally monitored the dynamics of gut microbiota in response to bowel cleaning and concurrent bacterial challenge infection. Our data show that the bowel preparation induced a persistent microbial perturbation, resulting in an incomplete spontaneous recovery 15 days after the procedure. A 12-day symbiotic intervention significantly enriched alpha diversity and restored the dysbiosis induced by the cleaning. The intervention also increased Firmicutes/Bacteroidota ratio and the abundance of several key beneficial bacteria in the genera Lactobacillus, Mucispirillum, and Butyricicoccus. Under infectious stress, bowel cleansing markedly aggravated colitis phenotypes, while the intervention alleviated crypt hyperplasia and attenuated inflammatory injury in mice infected with Citrobacter rodentium, resulting in a significant improvement in several colitis indicators. Mechanistically, the synbiotic enhanced the IL12/IFN-γ antimicrobial axis, increased the expression of Muc2 and sIgA, and improved bacterial interaction networks disrupted by challenge infection. Our findings demonstrate that FOS and C. butyricum act synergistically in promoting gut microbial homeostasis and host defense. Our strategy to take advantage of their strong synergy will facilitate the development of precision nutrition as a complement alternative for post-cleaning care, supporting their translational potential as functional adjuncts in peri-procedural disease management.