Monitoring Antifungal Resistance in a Global Collection of Invasive Yeasts and Molds: Application of CLSI Epidemiological Cutoff Values and Whole-Genome Sequencing Analysis for Detection of Azole Resistance in Candida albicans

The activity of 7 antifungal agents against 3,557 invasive yeasts and molds collected in 29 countries worldwide in 2014 and 2015 was evaluated. Epidemiological cutoff values (ECVs) published in the Clinical and Laboratory Standards Institute (CLSI) M59 document were applied for species with no clinical breakpoints. Echinocandin susceptibility rates were 95.9% to 100.0% for the 5 most commonCandida species, except for the rates forCandida parapsilosis to anidulafungin (88.7% susceptible, 100.0% wild type). Rates of fluconazole resistance ranged from 8.0% forCandida glabrata to 0.4% forCandida albicans . SevenCandida species displayed 100.0% wild-type amphotericin B MIC results, andCandida dubliniensis andCandida lusitaniae exhibited wild-type echinocandin MIC results. The highest fluconazole, voriconazole, and posaconazole MIC values forCryptococcus neoformans var.grubii were 8 μg/ml, 0.12 μg/ml, and 0.25 μg/ml, respectively.Aspergillus fumigatus isolates were 100.0% wild type for caspofungin and amphotericin B, but 3 (0.8%) of these isolates were non-wild type to itraconazole (2 isolates) or voriconazole (1 isolate). Mutations inFKS hot spot (HS) regions were detected among 13/20Candida isolates displaying echinocandin MICs greater than the ECV (16 of these 20 isolates wereC. glabrata ). Most isolates carrying mutations inFKS HS regions were resistant to 2 or more echinocandins. Five fluconazole-nonsusceptibleC. albicans isolates were submitted to whole-genome sequencing analysis. Gain-of-function,Erg11 heterozygous, andErg3 homozygous mutations were observed in 1 isolate each. One isolate displayed MDR1 promoter allele alterations associated with azole resistance. Elevated levels of expression of MDR1 or CDR2 were observed in 3 isolates and 1 isolate, respectively. Echinocandin and azole resistance is still uncommon among contemporary fungal isolates; however, mechanisms of resistance to antifungals were observed amongCandida spp., showing that resistance can emerge and monitoring is warranted.