Evaluation of the MIC test strips for antifungal susceptibility testing of <i>Candidozyma auris</i> ( <i>Candida auris</i> ) using a representative international collection of isolates

Abstract

ABSTRACT We compared MIC test strips (MTS) with the reference Clinical and Laboratory Standards Institute (CLSI) broth microdilution method using an international panel of 100 Candidozyma auris ( Candida auris ) isolates belonging to different clades. The agreement (±1 twofold dilution) between the methods and the categorical agreement (CA) based on the Centers for Disease Control and Prevention’s (CDC’s) tentative resistance breakpoints and MTS-specific wild-type upper limit values (WT-ULVs) were determined. The MTS-CLSI agreement was poor to weak for posaconazole (3%), itraconazole (20%), voriconazole (31%), and 5-flucytosine (37%), and moderate to strong for isavuconazole (58%), anidulafungin (68%), caspofungin (72%), micafungin (77%), and amphotericin B (85%). Most fluconazole MICs were off-scale, precluding a corresponding estimation. Significant interpretation discrepancies were recorded using the CDC’s breakpoints for amphotericin B (66% CA, 34% major errors; MaEs), but not for fluconazole (98% CA, 1% MaEs, 1% very major errors; VmEs), anidulafungin (97% CA, 3% MaEs, 0% VmEs), micafungin (99% CA, 1% MaEs, 0% VmEs), and caspofungin (95% CA, 5% MaEs, 0% VmEs). Discrepancies were minimized using the amphotericin B method-specific WT-ULV of 4 mg/L (98% CA, 2% MaEs). The MTS-specific WT-ULVs of echinocandins could help to detect 100% of FKS1 mutants. MTS generated higher MICs than the CLSI for azoles and 5-flucytosine. MTS could accurately detect fluconazole and echinocandin resistance among C. auris isolates. Nevertheless, it overestimated amphotericin B resistance as per the CDC’s breakpoint of 2 mg/L. This can be improved by using the MTS-specific WT-ULV of 4 mg/L. IMPORTANCE Candidozyma auris ( Candida auris ) may exhibit resistance to multiple and sometimes even all currently available classes of antifungals. Hence, antifungal susceptibility testing (AFST) is of key importance to guide the clinician in therapeutic decision-making and to detect novel patterns of resistance. Gradient diffusion strips, referred to both Etest and MIC test strip (MTS), are broadly used in laboratory routine for AFST of yeasts. We therefore compared MTS with the reference Clinical and Laboratory Standards Institute (CLSI) broth microdilution method using an international panel of 100 C . auris isolates belonging to different clades. Significant interpretation discrepancies were recorded for amphotericin B (66% categorical agreement, 34% major errors), which could be minimized using the amphotericin B method-specific wild-type upper limit value of 4 mg/L. MTS generated higher MICs than the CLSI for azoles and 5-flucytosine. MTS could accurately detect fluconazole and echinocandin resistance.

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