The goal of this clinical trial is to learn if oral lyophilized fecal microbiota therapy (ORAL-LYO-FMT) helps treat diarrhea-predominant irritable bowel syndrome (IBS-D) and prevent the recurrence of Clostridioides difficile infection (rCDI). The main questions it aims to answer are:
* Does ORAL-LYO-FMT reduce IBS symptoms?
* Does it prevent rCDI after treatment?
* What side effects or safety concerns might occur? Researchers will compare ORAL-LYO-FMT to a placebo (a look-alike capsule with no active treatment) to see how well it works.
Participants will:
* Be randomly assigned to take ORAL-LYO-FMT or placebo for up to 7 weeks
* Take capsules three times per week (Monday, Wednesday, Friday)
* Complete health questionnaires and have follow-up visits by phone or in person for up to 6 months The trial also looks at changes in quality of life, mood, and new or ongoing medical conditions over time.