Identification of a Cryptococcus neoformans Cytochrome P450 Lanosterol 14α-Demethylase (Erg11) Residue Critical for Differential Susceptibility between Fluconazole/Voriconazole and Itraconazole/Posaconazole

Abstract

ABSTRACTCryptococcus neoformansstrains resistant to azoles due to mutations causing alterations in theERG11gene, encoding lanosterol 14α-demethylase, have rarely been reported. In this study, we have characterized aC. neoformansserotype A strain that is resistant to high concentrations of fluconazole (FLC). This strain, which was isolated from an FLC-treated patient, contained five missense mutations in theERG11gene compared to the sequence of reference strain H99. Molecular manipulations of theERG11gene coupled with susceptibility to triazole revealed that a single missense mutation resulting in the replacement of tyrosine by phenylalanine at amino acid 145 was sufficient to cause the high FLC resistance of the strain. Importantly, this newly identified point mutation in theERG11gene ofC. neoformansafforded resistance to voriconazole (VRC) but increased susceptibility to itraconazole (ITC) and posaconazole (PSC), which are structurally similar to each other but distinct from FLC/VRC. Thein vitrosusceptibility/resistance of the strains with or without the missense mutation was reflected in the therapeutic efficacy of FLC versus ITC in the animals infected with the strains. This study shows the importance of the Y145F alteration of Erg11 inC. neoformansfor manifestation of differential susceptibility toward different triazoles. It underscores the necessity ofin vitrosusceptibility testing for each FLC-resistantC. neoformansclinical isolate against different groups of azoles in order to assist patient management.