Cloning of the lanosterol 14-α-demethylase ( ERG11 ) gene in Trichosporon asahii: a possible association between G453R amino acid substitution and azole resistance in T. asahii.

Lanosterol 14-alpha-demethylase ( Erg11 protein; Erg11p ), encoded by the ERG11 gene, is the primary target of azoles. Recently, a change in affinity of this enzyme for azoles has been reported as a resistance mechanism in several fungal species. Trichosporon asahii ( T. asahii) is susceptible to fluconazole (FLC). This report identified the ERG11 gene of T. asahii (NCBI accession; HQ176415). The Erg11p of T. asahii, presumed from the DNA sequence, was closely related to the Erg11p of Cryptococcus neoformans. Furthermore, a FLC-susceptible strain was cultured in medium containing FLC at concentrations from 4.0 to 16 mu g mL-1 in order to analyze the development of FLC resistance in T. asahii. The degree of resistance was related to the FLC concentration of the growth medium. One highly resistant strain that was cultured in the medium containing 16 mu g mL-1 FLC contained 1 point mutation (G1357C) that caused a single amino acid substitution at G453R. This amino acid is highly conserved among major fungal pathogens, and it is in a region very close to the heme-binding domain, which is characteristic of the cytochrome P450 superfamily, the primary target for the azole class of antifungal agents. This amino acid substitution may have caused the high resistance to azoles in T. asahii.