Mechanism of Fluconazole Resistance in Candida krusei

The mechanisms of fluconazole resistance in three clinical isolates ofCandida krusei were investigated. Analysis of sterols of organisms grown in the absence and presence of fluconazole demonstrated that the predominant sterol ofC. krusei is ergosterol and that fluconazole inhibits 14α-demethylase in this organism. The 14α-demethylase activity in cell extracts ofC. krusei was 16- to 46-fold more resistant to inhibition by fluconazole than was 14α-demethylase activity in cell extracts of two fluconazole-susceptible strains ofCandida albicans . Comparing the carbon monoxide difference spectra of microsomes fromC. krusei with those of microsomes fromC. albicans indicated that the total cytochrome P-450 content ofC. krusei is similar to that ofC. albicans . The Soret absorption maximum in these spectra was located at 448 nm forC. krusei and at 450 nm forC. albicans . Finally, the fluconazole accumulation of two of theC. krusei isolates was similar to if not greater than that ofC. albicans . Thus, there are significant qualitative differences between the 14α-demethylase ofC. albicans andC. krusei . In addition, fluconazole resistance in these strains ofC. krusei appears to be mediated predominantly by a reduced susceptibility of 14α-demethylase to inhibition by this drug.