Comparison of a 2,3-Bis(2-Methoxy-4-Nitro-5-Sulfophenyl)-5-[(Phenylamino)Carbonyl]-2H-Tetrazolium Hydroxide (XTT) Colorimetric Method with the Standardized National Committee for Clinical Laboratory Standards Method of Testing Clinical Yeast Isolates for Susceptibility to Antifungal Agents

MICs for clinical Candida and Cryptococcus isolates were determined by a method incorporating the colorimetric indicator 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2H-tetrazolium hydroxide (XTT), and the results were compared with MICs obtained by the National Committee for Clinical Laboratory Standards approved standard method (M27-A). One hundred percent of all isolates demonstrated agreement within 2 dilutions between the MICs of amphotericin B, fluconazole, itraconazole, ketoconazole, and flucytosine obtained by the two methods. These data suggest that an XTT-based method could provide a useful means for the determination of antifungal susceptibility of yeasts.