Antibiotic course frequency and recovery strategies alter gut microbial composition and metabolism.

Antibiotics profoundly alter the gut microbiome, but how exposure frequencies shape microbial recovery remains unclear. The effectiveness of post-antibiotic interventions, e.g. probiotics or autologous fecal microbiota transplantation, (aFMT) requires further exploration. This study investigated how antibiotic course timing and recovery strategies influence gut microbiome and metabolism in male Wistar rats. A single oral dose of vancomycin-ciprofloxacin (VC) caused rapid urinary and fecal metabolic shifts within 8-12 h and reduced bacterial α-diversity in cecal and colonic contents. When three VC courses were administered at regular (every 3 weeks; VCr) or irregular (1-3 weeks; VCi) intervals, VCr showed greater suppression of fecal α-diversity and stronger disruption of amino acid and host-microbial co-metabolism than VCi. Over the 3-week recovery period, VCr exhibited slower fecal α-diversity restoration; at week 3, β-diversity remained significantly different between groups, and cecal butyrate levels were persistently reduced in VCr. Both groups showed elevated levels of 5-aminovalerate in feces and colon compared with controls, whereas only VCi showed reductions in jejunal and ileal amino acids. Probiotics or aFMT had limited influence on small intestinal alterations, though aFMT accelerated fecal α-diversity recovery, and both interventions promoted partial normalization of fecal amino acids and 5-aminovalerate, without achieving complete restoration. Overall, shorter antibiotic intervals exerted stronger effects on the small intestinal luminal chemical environment, whereas longer intervals led to greater suppression of colonic and fecal microbial metabolism. Probiotics and aFMT supported selective metabolic recovery without fully reversing antibiotics-induced disturbances, highlighting the need for more targeted restoration strategies across gastrointestinal regions.