Characterization of mechanisms of fluconazole resistance in a Candida albicans isolate from a Japanese patient with chronic mucocutaneous candidiasis

We examined the mechanisms of fluconazole resistance in a fluconazole-resistant Candida albicans isolate from a Japanese patient with chronic mucocutaneous candidiasis. It was demonstrated that the highly resistant phenotype of this strain was associated with combined mechanisms of the energy-dependent reduced intracellular accumulation of fluconazole, presumably due to the increased expression of the ATP-binding cassette efflux pump CDR gene(s), and the reduced affinity of the target enzyme, Erg11p, to fluconazole. In particular, the reduced affinity of Erg11p was considered to contribute largely to the fluconazole resistance in the TIMM3209 strain. Biochemical studies indicated that the Erg11p from the TIMM3209 strain showed reduced susceptibility both to fluconazole and itraconazole of cell-free ergosterol biosynthesis, and cytochrome P-450 also showed reduced affinity to fluconazole in the carbon monoxide-cytochrome P-450 complex formation assay. We identified two amino acid substitutions, Y132H and G448V, in Erg11p from the TIMM3209 strain. We found that the cytochrome P-450 from the TIMM3209 strain decayed during incubation at 37 C without fluconazole although it is unknown whether or not the phenomenon is linked to the resistant phenotype. These mutations are thought to confer the above-mentioned characteristics to Erg11p.