Patient description: The patient is a 60-year-old woman admitted to the stroke department with a recent history of a second course of intravenous antibiotics for aspiration pneumonia. She is febrile and complained of abdominal pain and diarrhea (bowel movements eight times in 3 hours, large volumes of greenish, liquid stool each time). The patient's abdomen is generally tender and distend with hyperactive bowel sounds. She is febrile (38.4°C), tachycardic (113/min) and hypotensive (80/40 mmHg). The stool samples must were positive for Clostridium difficile toxin.

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  Clostridium Difficile Infection Signed informed consent, indicating that the patient understands the purpose of and procedures required for the study. Patients who are unable to provide informed consent will not be included in the study. 2. Male or female patients ≥ 18 years of age. 3. Previously enrolled in Study SERES-004 and had CDI recurrence within 8 weeks after receipt of study drug, OR If not previously enrolled in Study SERES-004, a documented history of ≥ 3 episodes of CDI within the previous 9 months, inclusive of the current episode with ≥ 1 of the historical episodes having the date, test results, and antibiotic treatment received documented. Efforts should be made to acquire history of additional CDI episodes. 4. If not previously enrolled in Study SERES-004, a qualifying episode of CDI as defined by: 1. ≥ 3 unformed stools per day for 2 consecutive days 2. A positive C. difficile stool test 3. The requirement of CDI standard-of-care antibiotic therapy (defined as 10 to 21 days of treatment with vancomycin or fidaxomicin but excluding pulse-tapered antibiotic regimens). 4. An adequate clinical response defined as no evidence of diarrhea (< 3 unformed stools in 24 hours) for 2 or more consecutive days before randomization. 5. If female, patient is non-lactating, and is either: 1. Not of childbearing potential, defined as postmenopausal for at least 1 year or surgically sterile due to bilateral tubal ligation, bilateral oophorectomy, or hysterectomy. 2. Of childbearing potential and is practicing at least 1 highly effective method of birth control including the barrier method; oral or parenteral contraceptives; a vasectomized partner; or abstinence from sexual intercourse. The investigator will discuss with the patient the option of practicing more than 1 of the above methods for the duration of the study. 6. If male and partner is of childbearing potential, patient agrees to practice at least 1 highly effective method of birth control for the duration of the study. 7. Is not taking probiotics, or discontinues probiotics prior to study start and will not take probiotics for the duration of the study  Female patients who are pregnant, breastfeeding, lactating, or planning to become pregnant during the study. 2. Known or suspected toxic megacolon and/or known small bowel ileus. 3. Active irritable bowel syndrome with diarrhea within the previous 12 months. 4. Admitted to or expected to be admitted to an acute care facility or intensive care unit for medical reasons (not just boarding). Patients discharged from an acute care facility before Day 1 or residing in nursing homes or rehabilitation facilities may be enrolled. 5. Taking antibacterial therapy other than vancomycin (non-tapered) or fidaxomicin for most recent episode of CDI within 14 days before enrollment. A single-day antibiotic prophylactic regimen is permitted. 6. Use of any probiotics. 7. Major gastrointestinal surgery (e.g., significant bowel resection or diversion) within 3 months before enrollment (this does not appendectomy or cholecystectomy) or any history of total colectomy or bariatric surgery. 8. History of inflammatory bowel disease (ulcerative colitis, Crohn's disease, microscopic colitis) with diarrhea believed to be caused by active inflammatory bowel disease in the past 24 months. 9. Unable to stop loperamide, diphenoxylate/atropine, or cholestyramine before the study. 10. Unable to stop opiate treatment unless on a stable dose, including PRN dosing, as of onset of diarrhea and no increase in dose planned for the duration of the study. 11. Known positive stool cultures for other enteropathogens including, but not limited to, Salmonella, Shigella, and Campylobacter within the 30 days before enrollment. 12. Known stool studies positive for ova and/or parasites within the 30 days before enrollment. 13. Poor concurrent medical risks with clinically significant co-morbid disease such that, in the opinion of the investigator, the patient should not be enrolled. 14. Received an investigational vaccine against C. difficile. 15. Known active intravenous drug or alcohol abuse or other drugs of abuse