Azole resistance in Cryptococcus gattii from the Pacific Northwest: Investigation of the role of ERG11

Antimicrob Agents Chemother. 2013 Nov;57(11):5478-85. doi: 10.1128/AAC.02287-12. Epub 2013 Aug 26.

Abstract

Cryptococcus gattii is responsible for an expanding epidemic of serious infections in Western Canada and the Northwestern United States (Pacific Northwest). Some patients with these infections respond poorly to azole antifungals, and high azole MICs have been reported in Pacific Northwest C. gattii. In this study, multiple azoles (but not amphotericin B) had higher MICs for 25 Pacific Northwest C. gattii than for 34 non-Pacific Northwest C. gattii or 20 Cryptococcus neoformans strains. We therefore examined the roles in azole resistance of overexpression of or mutations in the gene (ERG11) encoding the azole target enzyme. ERG11/ACT1 mRNA ratios were higher in C. gattii than in C. neoformans, but these ratios did not differ in Pacific Northwest and non-Pacific Northwest C. gattii strains, nor did they correlate with fluconazole MICs within any group. Three Pacific Northwest C. gattii strains with low azole MICs and 2 with high azole MICs had deduced Erg11p sequences that differed at one or more positions from that of the fully sequenced Pacific Northwest C. gattii strain R265. However, the azole MICs for conditional Saccharomyces cerevisiae erg11 mutants expressing the 5 variant ERG11s were within 2-fold of the azole MICs for S. cerevisiae expressing the ERG11 gene from C. gattii R265, non-Pacific Northwest C. gattii strain WM276, or C. neoformans strains H99 or JEC21. We conclude that neither ERG11 overexpression nor variations in ERG11 coding sequences was responsible for the high azole MICs observed for the Pacific Northwest C. gattii strains we studied.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amphotericin B / pharmacology
  • Antifungal Agents / pharmacology
  • Canada / epidemiology
  • Cryptococcosis / epidemiology
  • Cryptococcosis / microbiology
  • Cryptococcus gattii / drug effects
  • Cryptococcus gattii / enzymology
  • Cryptococcus gattii / genetics*
  • Cryptococcus neoformans / drug effects
  • Cryptococcus neoformans / enzymology
  • Cryptococcus neoformans / genetics*
  • Drug Resistance, Fungal / genetics*
  • Fluconazole / pharmacology
  • Fungal Proteins / genetics*
  • Fungal Proteins / metabolism
  • Gene Expression
  • Genetic Complementation Test
  • Humans
  • Microbial Sensitivity Tests
  • Mutation
  • Northwestern United States / epidemiology
  • Saccharomyces cerevisiae / drug effects
  • Saccharomyces cerevisiae / enzymology
  • Saccharomyces cerevisiae / genetics
  • Sterol 14-Demethylase / genetics*
  • Sterol 14-Demethylase / metabolism

Substances

  • Antifungal Agents
  • Fungal Proteins
  • Amphotericin B
  • Fluconazole
  • Sterol 14-Demethylase