["Second look" at cytotoxin B of Clostridium difficile in the course of diarrhea associated with antibiotic therapy].

UNLABELLED: Clostridium difficile is a sporulated obligate anaerobe responsible for most cases of antibiotic-associated colitis, for 15 to 25% of cases of antibiotic-related diarrhea, and for a substantial proportion of nosocomial infections. The most important laboratory test for the diagnosis of C. difficile infection is examination of the stool for C. difficile toxins A and/or B. Detection of cytotoxin B using the direct cytotoxicity assay (D-CA) is the gold standard test. Whether routine isolation of the organism from stool is warranted remains controversial.
OBJECTIVES: To evaluate second-look CA done on C. difficile culture-positive filtrates from stool samples negative by the D-CA.
METHODS: 300 consecutive stool samples sent to the Alfred Fournier Institute from April through October 1998 for a CA were routinely cultured on modified Cefoxitin Cycloserine Fructose Agar medium (CCFA). All CA-negative samples that grew C. difficile were examined by second-look CA.
RESULTS: 245 stool specimens (81.7%) were negative by both CA and culture. The remaining 55 specimens all yielded C. difficile by culture; 32 (58.2%) had a positive D-CA and nine (16.4%) a negative D-CA with a positive second-look CA done on culture filtrates.
CONCLUSION: Our data suggest that stool specimens sent for a direct CA should be routinely cultured to provide material for a second-look CA on culture-positive filtrates if the first CA prove negative. Culturing also allows to study antimicrobial drug resistance phenotypes and epidemiological markers.