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,  Clostridioides Difficile Infection Cohort 1 1. Previously enrolled in Study SERES-012, had CDI recurrence within 8 weeks after receipt of study drug, and have completed their SERES-012 Week 8 visit. 2. Signed informed consent prior to initiation of any study-specific procedure or treatment. The subject must be able to provide written informed consent and understand the potential risks and benefits from study enrollment and treatment. 3. The CDI recurrence in Study SERES-012 must have met the protocol definition of ≥ 3 unformed stools per day over 2 consecutive days, a positive C. difficile stool test, and assessment by the investigator that the clinical condition of the subject warranted treatment. Cohort 1  Female subjects 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. Admitted to or expected to be admitted to an intensive care unit for medical reasons (not just boarding). Note: nursing homes, rehabilitation, assisted living centers and acute care hospitals are acceptable. 4. Absolute neutrophil count of <500 cells/ml3. 5. 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 (bariatric surgery which does not disrupt the gastrointestinal lumen, i.e., restrictive procedures such as banding, are permitted). 6. History of active inflammatory bowel disease (ulcerative colitis, Crohn's disease, microscopic colitis) with diarrhea believed to be caused by active inflammatory bowel disease in the past 3 months. 7. Concurrent intensive induction chemotherapy, radiotherapy, or biologic treatment for active malignancy (subjects on maintenance chemotherapy may only be enrolled after consultation with the study medical monitor). 8. Any history of fecal microbiota transplantation (FMT). Cohort 2 1. Subjects 18 years of age or older who had one or more CDI recurrence (as confirmed by a C. difficile stool toxin test) within 12 months and have responded to a course of standard of care antibiotic treatment. 2. Signed informed consent prior to initiation of any study-specific procedure or treatment. The subject must be able to provide written informed consent and understand the potential risks and benefits from study enrollment and treatment. Cohort 2 (all Cohort 1 [#1-8 above] plus the below addition criterion) 9. Previously enrolled in a Seres Therapeutics clinical study