Resistance to itraconazole in Aspergillus nidulans and Aspergillus fumigatus is conferred by extra copies of the A. nidulans P-450 14alpha-demethylase gene, pdmA

J Antimicrob Chemother. 2001 Jul;48(1):75-81. doi: 10.1093/jac/48.1.75.


Triazoles selectively inhibit the cytochrome P-450-dependent C-14 lanosterol alpha-demethylase (P-450 14 alpha DM), a key enzyme in ergosterol biosynthesis in fungi. To investigate mechanisms of triazole resistance in a mould, we used Aspergillus nidulans, a genetically amenable model fungus closely related to more pathogenic members of the genus. We selected for genes that would give resistance to itraconazole following transformation with a high copy genomic library of A. nidulans. In all the resistant colonies that we isolated, resistance was conferred by extra copies of the A. nidulans P-450 14 alpha DM gene, pdmA. We determined that in A. nidulans, extra copies of pdmA increase the MIC for itraconazole 36 times over wild-type controls. Similarly, transformation of an Aspergillus fumigatus strain with pITZR1 resulted in increased resistance to itraconazole. Our results indicate that triazole resistance in clinical isolates of moulds may result from amplification or overexpression of the P-450 14 alpha DM and demonstrate the utility of A. nidulans as a promising model fungus for the analysis of drug resistance and susceptibility in the pathogenic fungus A. fumigatus.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Aspergillus fumigatus / drug effects*
  • Aspergillus fumigatus / enzymology
  • Aspergillus fumigatus / genetics
  • Aspergillus nidulans / drug effects*
  • Aspergillus nidulans / enzymology
  • Aspergillus nidulans / genetics
  • Cytochrome P-450 Enzyme System / genetics*
  • Drug Resistance, Microbial
  • Gene Dosage
  • Itraconazole / pharmacology*
  • Microbial Sensitivity Tests
  • Molecular Sequence Data
  • Oxidoreductases / genetics*
  • Sterol 14-Demethylase


  • Itraconazole
  • Cytochrome P-450 Enzyme System
  • Oxidoreductases
  • Sterol 14-Demethylase