ECOSPOR IV: An Open-Label Extension of Study SERES 012 Evaluating SER-109 in Subjects With Recurrent Clostridium Difficile Infection

This is an open-label extension of Study SERES-012. Subjects who had a CDI recurrence in
Study SERES-012 within 8 weeks of receipt of study drug, have responded to a course of
standard of care (SOC) antibiotic treatment, and who have completed their SERES-012 Week 8
visit will receive an oral dose of SER-109. A treatment regimen of SER-109 is defined as an
oral dose of SER-109 in 4 capsules once daily for 3 consecutive days.

Approximately 100 eligible subjects with recurrent CDI disease from Study SERES-012 are
expected to enroll. Screening for this study will begin at the Week 8 Visit of Study
SERES-012.

Inclusion Criteria:

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.

Exclusion Criteria:

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 include 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)