Subjects who had a CDI recurrence in Study SERES-012 within 8 weeks of receipt of study drug will receive an oral dose of SER-109 in 4 capsules once daily for 3 consecutive days. The purpose of this study is to assess safety and efficacy of SER-109 in reducing recurrence of Clostridium difficile infection (CDI) in adults who had a CDI recurrence within 8 weeks after receipt of SER-109 or Placebo in Study SERES-012.