High-level expression of cyp51B in azole-resistant clinical Aspergillus fumigatus isolates.

OBJECTIVES: Resistance to azole antifungal drugs in Aspergillus fumigatus that is not mediated by target gene mutations is now common in some locations. The aim of this study was to investigate possible new mechanisms of resistance in non-target resistance. METHODS: Twelve azole-resistant A. fumigatus isolates previously shown not to carry mutations in cyp51A were tested to determine whether the alternative cyp51B gene was overexpressed. RESULTS: Of 12 isolates one showed overinduction of cyp51B after exposure to itraconazole and another showed high constitutive expression of cyp51B. CONCLUSIONS: cyp51B overexpression is a possible azole resistance mechanism in A. fumigatus.