Infection with Toxin A-Negative, Toxin B-Negative, Binary Toxin-Positive Clostridium difficile in a Young Patient with Ulcerative Colitis.

Large clostridial toxin-negative, binary toxin-positive (A(-) B(-) CDT(+)) strains of Clostridium difficile are almost never associated with clinically significant C. difficile infection (CDI), possibly because such strains are not detected by most diagnostic methods. We report the isolation of an A(-) B(-) CDT(+) ribotype 033 (RT033) strain of C. difficile from a young patient with ulcerative colitis and severe diarrhea.