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

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Two variations of an egg yolk agar base medium containing cycloserine, cefoxitin, and fructose (CCFA), one with 250 μg and the other with 500 μg of cycloserine/ml of agar medium were compared to study the effect of the cycloserine concentration on recovery ofClostridium difficile from stool samples. In addition, the role of prior anaerobic reduction of these media in the detection ofClostridium 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 μg of cycloserine/ml of agar combined with 4 h of anaerobic reduction prior to specimen inoculation increased the rate of isolation of toxigenicClostridium difficile from clinical specimens from 6 to 17% (p < 0.001). Combining direct detection of stool toxin and properly performed culture for toxigenicClostridium difficile enhances the potential for diagnosis of CDAD. For optimal performance the culture medium should contain the originally proposed cycloserine concentration of 500 μg/ml of agar and should be anaerobically reduced at least 4 h prior to specimen inoculation.