Echinocandin susceptibility testing of Candida species: Comparison of EUCAST EDef 7.1, CLSI M27-A3, etest, disk diffusion, and agar dilution methods with RPMI and isosensitest media

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Abstract

This study compared nine susceptibility testing methods and 12 endpoints for anidulafungin, caspofungin, and micafungin with the same collection of blinded FKS hot spot mutant (n = 29) and wild-type isolates (n = 94). The susceptibility tests included EUCAST Edef 7.1, agar dilution, Etest, and disk diffusion with RPMI-1640 plus 2% glucose (2G) and IsoSensitest-2G media and CLSI M27A-3. Microdilution plates were read after 24 and 48 h. The following test parameters were evaluated: fks hot spot mutants overlapping the wild-type distribution, distance between the two populations, number of very major errors (VMEs; fks mutants misclassified as susceptible), and major errors (MEs; wild-type isolates classified as resistant) using a wild-type-upper-limit value (WT-UL) (two twofold-dilutions higher than the MIC50) as the susceptibility breakpoint. The methods with the lowest number of errors (given as VMEs/ MEs) across the three echinocandins were CLSI (12%/1%), agar dilution with RPMI-2G medium (14%/ 0%), and Etest with RPMI-2G medium (8%/3%). The fewest errors overall were observed for anidulafungin (4%/1% for EUCAST, 4%/3% for CLSI, and 3%/9% for Etest with RPMI-2G). For micafungin, VME rates of 10 to 71% were observed. For caspofungin, agar dilution with either medium was superior (VMEs/MEs of 0%/1%), while CLSI, EUCAST with IsoSensitest-2G medium, and Etest were less optimal (VMEs of 7%, 10%, and 10%, respectively). Applying the CLSI breakpoint (S ≤ 2 μg/ml) for CLSI results, 89.2% fks hot spot mutants were classified as anidulafungin susceptible, 60.7% as caspofungin susceptible, and 92.9% as micafungin susceptible. In conclusion, no test was perfect, but anidulafungin susceptibility testing using the WT-UL to define susceptibility reliably identified fks hot spot mutants. Copyright © 2010, American Society for Microbiology. All Rights Reserved.

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Arendrup, M. C., Garcia-Effron, G., Lass-Flörl, C., Lopez, A. G., Rodriguez-Tudela, J. L., Cuenca-Estrella, M., & Perlin, D. S. (2010). Echinocandin susceptibility testing of Candida species: Comparison of EUCAST EDef 7.1, CLSI M27-A3, etest, disk diffusion, and agar dilution methods with RPMI and isosensitest media. Antimicrobial Agents and Chemotherapy, 54(1), 426–439. https://doi.org/10.1128/AAC.01256-09

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