['clostridium difficile', 'clostridium infections']
['syn-004', 'placebo']

        Inclusion Criteria:

          -  Expected minimum hospital stay of 5 days

          -  Expected ≥5 day course of intravenous (IV) ceftriaxone alone or in combination with a
             macrolide

          -  Clinical diagnosis of moderate to severe lower respiratory tract infection consisting
             of signs and symptoms of a lower respiratory tract infection and Pneumonia Severity
             Index (PSI/PORT) score for CAP of 90-130, inclusive. Evidence of a new or progressive
             infiltrate on chest x-ray is recommended.

        Exclusion Criteria:

          -  Presence of a diarrheal illness within 72 hours prior to randomization

          -  Current treatment for CDAD or ongoing active CDI, as evidenced by clinical signs of
             diarrhea along with the presence of toxin A and/or B (or their respective genes, tcdA
             and/or tcdB) of C. difficile in the stool

          -  Number of previous CDAD episodes >1 within 12 weeks of randomization and no C.
             difficile infection (CDI) within 4 weeks of randomization

          -  Use of antibiotics within 1 month of start of study drug except for the current
             illness.
      