EUCAST has so far not defined breakpoints for C. auris, due to the lack of clinical outcome data and the high degree of clonality of this species. Thus, there is currently insufficient evidence to set breakpoints, but EUCAST are aware of other provisional cut-offs which are being used elsewhere, and in some commercial systems. Antifungal susceptibility testing of amphotericin B against C. auris has been associated with overestimation of resistance due to greater variability and wider MIC distributions and/or higher MICs in several studies, which are briefly summarised below.
Consequently, EUCAST warns against the use of the following tests for amphotericin B MIC testing of C. auris with S/R breakpoints of S ≤ 1 mg/L / R > 1 mg/L:
- Etest, (Etest, bioMerieux), gradient strip
- Mic Test Strip (MTS, Liofilchem), gradient strip
- Vitek 2 system (bioMerieux)
- Sensititre Yeast One (Thermofisher)