This study compared the YeastOne and reference CLSI M38-A2 broth microdilution methods for antifungal susceptibility testing of Aspergillus species. The minimum inhibitory concentrations (MICs) of antifungal agents against 100 isolates, comprising 31 Aspergillus fumigatus (5 TR34/L98H isolates), 23 Aspergillus flavus, 13 Aspergillus terreus, and 10 Aspergillus niger clinical isolates, and 23 A. fumigatus environmental isolates (19 TR34/L98H isolates), were determined. The overall agreement (within two twofold dilutions) between the two methods was 100%, 95%, 92%, and 90% for voriconazole, posaconazole, itraconazole, and amphotericin B, respectively. The voriconazole geometric mean (GM) MICs from both methods were nearly identical for all isolates, whereas the itraconazole and posaconazole YeastOne GM MICs were about one dilution lower than the reference GM MICs. In contrast, the amphotericin B YeastOne GM MIC was 3.3-fold higher than the reference GM MIC. Of 24 TR34/L98H A. fumigatus isolates, the categorial agreement (classified according to the EUCAST clinical breakpoints) was 100%, 91.7%, and 83.3% for itraconazole, voriconazole, and posaconazole, respectively. Of four A. niger isolates, itraconazole MICs were read as > 8 mg/L by M38-A2 due to trailing growth in wells containing itraconazole concentrations of 0.5 to 8 mg/L, whereas the corresponding itraconazole MICs by YeastOne were all ≤ 0.25 mg/L, without trailing growth. These data suggested that YeastOne could be a suitable alternative for azole susceptibility testing of Aspergillus species and for detecting TR34/L98H A. fumigatus. Nevertheless, YeastOne tended to yield higher amphotericin B MICs and failed to detect A. niger isolates which exhibited trailing growth with itraconazole.

Comparison of the Sensititre YeastOne with CLSI M38-A2 microdilution methods for MIC determination of amphotericin B and azoles against Aspergilli