In vitro activity of voriconazole and other antifungal agents against clinical isolates of Candida glabrata and Candida krusei

The antifungal susceptibility of 309 Candida glabrata and 63 Candida krusei clinical isolates was tested via the Sensititre YeastOne-3 system (Trek Diagnostic Systems, East Grinstead, UK) to compare the in vitro activity of voriconazole with that of five other antifungal agents (amphotericin B, fluconazole, itraconazole, ketoconazole, and flucytosine). Voriconazole was highly active (MIC90, 0.5 μg/ml) against isolates of both species, including those for which the MICs of itraconazole and fluconazole were high (MIC90s of itraconazole, 2 μg/ml for C. glabrata and 0.5 μg/ml for C. krusei; MIC90s of fluconazole, 32 μg/ml for C. glabrata and 64 μg/ml for C. krusei). Ketoconazole MIC90 values for both species were identical to those of voriconazole. The MIC90 of amphotericin B was similar for both species (0.125 μg/ml for C. glabrata and 0.25 μg/ml for C. krusei). As expected, flucytosine was only moderately active against C. krusei isolates (MIC90, 16 μg/ml) but was highly active against C. glabrata isolates (MIC90, 0.03 μg/ml). Potential cross-resistance within the azole class was noted for some strains of C. glabrata (5.5%) that presented high MIC values for all the azoles tested. In order to consider voriconazole a viable alternative to other triazoles for the treatment of infections caused by Candida species, susceptibility testing of all clinically significant isolates of C. glabrata and C. krusei is recommended because of the potential for azole cross-resistance. The Sensititre YeastOne-3 seems to be a suitable commercial tool for this purpose.