Aspergillus fumigatus Intrinsic Fluconazole Resistance Is Due to the Naturally Occurring T301I Substitution in Cyp51Ap.

Aspergillus fumigatus intrinsic fluconazole resistance has been demonstrated to be linked to the CYP51A gene, although the precise molecular mechanism has not been elucidated yet. Comparisons between A. fumigatus Cyp51Ap and Candida albicans Erg11p sequences showed differences in amino acid residues already associated with fluconazole resistance in C. albicans The aim of this study was to analyze the role of the natural polymorphism I301 in Aspergillus fumigatus Cyp51Ap in the intrinsic fluconazole resistance phenotype of this pathogen. The I301 residue in A. fumigatus Cyp51Ap was replaced with a threonine (analogue to T315 at Candida albicans fluconazole-susceptible Erg11p) by changing one single nucleotide in the CYP51A gene. Also, a CYP51A knockout strain was obtained using the same parental strain. Both mutants' antifungal susceptibilities were tested. The I301T mutant exhibited a lower level of resistance to fluconazole (MIC, 20 μg/ml) than the parental strain (MIC, 640 μg/ml), while no changes in MIC were observed for other azole- and non-azole-based drugs. These data strongly implicate the A. fumigatus Cyp51Ap I301 residue in the intrinsic resistance to fluconazole.