Role of culture and toxin detection in laboratory testing for diagnosis of Clostridium difficile-associated diarrhea

Two variations of an egg yolk agar base medium containing cycloserine, cefoxitin, and fructose (CCFA), one with 250 micrograms and other with 500 micrograms of cycloserine/ml of agar medium were compared to study the effect of the cycloserine concentration on recovery of Clostridium difficile from stool samples. In addition, the role of prior anaerobic reduction of these media in the detection of Clostridium difficile-associated diarrhea (CDAD) was tested. Each medium was studied over a two-month period, with outcome compared between the testing periods and to historical data from our institution. Clinical correlation of test results was performed. The use of the originally described formulation of CCFA with 500 microgram of cycloserine/ml of agar combined with 4 h of anaerobic reduction prior to specimen inoculation increased the rate of isolation of toxigenic Clostridium difficile from clinical specimens from 6 to 17% (p < 0.001). Combining direct detection of stool toxin and properly performed culture for toxigenic Clostridium difficile enhances the potential for diagnosis of CDAD. For optimal performance the culture medium should contain the originally proposed cycloserine concentration of 500 microgram/ml of agar and should be anaerobically reduced at least 4 h prior to specimen inoculation.