Method-Dependent Epidemiological Cutoff Values for Detection of Triazole Resistance in Candida and Aspergillus Species for the Sensititre YeastOne Colorimetric Broth and Etest Agar Diffusion Methods

Although the Sensititre Yeast-One (SYO) and Etest methods are widely utilized, interpretive criteria are not available for triazole susceptibility testing of Candida or Aspergillus species. We collected fluconazole, itraconazole, posaconazole, and voriconazole SYO and Etest MICs from 39 laboratories representing all continents for (method/agent-dependent) 11,171 Candida albicans , 215  C. dubliniensis , 4,418  C. glabrata species complex, 157  C. guilliermondii ( Meyerozyma guilliermondii ), 676  C. krusei ( Pichia kudriavzevii ), 298  C. lusitaniae ( Clavispora lusitaniae ), 911  C. parapsilosis sensu stricto , 3,691  C. parapsilosis species complex, 36  C. metapsilosis , 110  C. orthopsilosis , 1,854  C. tropicalis , 244 Saccharomyces cerevisiae , 1,409 Aspergillus fumigatus , 389  A. flavus , 130  A. nidulans , 233  A. niger , and 302  A. terreus complex isolates. SYO/Etest MICs for 282 confirmed non-wild-type (non-WT) isolates were included: ERG11 ( C. albicans ), ERG11 and MRR1 ( C. parapsilosis ), cyp51A ( A. fumigatus ), and CDR2 and CDR1 overexpression ( C. albicans and C. glabrata , respectively). Interlaboratory modal agreement was superior by SYO for yeast species and by the Etest for Aspergillus spp. Distributions fulfilling CLSI criteria for epidemiological cutoff value (ECV) definition were pooled, and we proposed SYO ECVs for S. cerevisiae and 9 yeast and 3 Aspergillus species and Etest ECVs for 5 yeast and 4 Aspergillus species. The posaconazole SYO ECV of 0.06 µg/ml for C. albicans and the Etest itraconazole ECV of 2 µg/ml for A. fumigatus were the best predictors of non-WT isolates. These findings support the need for method-dependent ECVs, as, overall, the SYO appears to perform better for susceptibility testing of yeast species and the Etest appears to perform better for susceptibility testing of Aspergillus spp. Further evaluations should be conducted with more Candida mutants.