Aspergillus fumigatus intrinsic fluconazole resistance is due to the naturally occurring T301I substitution in Cyp51Ap

Abstract

Aspergillus fumigatus intrinsic fluconazole resistance has been demonstrated to be linked to the CYP51A gene, although the precisemolecular mechanism has not been elucidated yet. Comparisons between A. fumigatus Cyp51Ap and Candida albicansErg11p sequences showed differences in amino acid residues already associated with fluconazole resistance in C. albicans. Theaim of this study was to analyze the role of natural polymorphism I301 in Aspergillus fumigatus Cyp51Ap in the intrinsic fluconazoleresistance phenotype of this pathogen. The I301 residue in A. fumigatus Cyp51Ap was replaced with a threonine (analogueto T315 at Candida albicans fluconazole-susceptible Erg11p) by changing one single nucleotide in CYP51A gene. Also, aCYP51A knockout strain was obtained using the same parental strain. Both mutants? antifungal susceptibilities were tested. TheI301T mutant exhibited a lower level of resistance to fluconazole (MIC, 20 g/ml) than the parental strain (MIC, 640 g/ml),while no changes in MIC were observed for other azole- and non-azole-based drugs. These data strongly implicate the A. fumigatusCyp51Ap I301 residue in the intrinsic resistance to fluconazole.