Invasive candidiasis results in high morbidity and mortality especially in immunocompromised patients. Having an early and accurate antifungal susceptibility result is important for appropriate patient treatment. Sensititre YeastONE has good concordance with the gold standard CLSI reference method for Candida susceptibility testing and is therefore a widely utilised commercial method of determining Candida susceptibility. The automated antifungal susceptibility testing of yeasts by Vitek 2 AST YS08 has clear advantages in decreased turn-around time, reduced costs and ease of use. However, there is limited data regarding its performance.
The purpose of the study was to evaluate the latest Vitek 2 AST YS08 yeast antifungal susceptibility card in comparison to the Sensititre YeastONE Y010 susceptibility system for antifungal susceptibility testing.
A total of 68 clinical isolates of Candida species, many known to have antifungal resistance, included Candida albicans (20), Candida glabrata (21), Candida tropicalis (9), Candida parapsilosis (10) and Candida krusei (8), were tested by Vitek 2 AST YS08 in comparison to the commercial Sensititre YeastONE method. Essential agreement (EA) was defined as ≤2 dilution difference and categorical agreement (CA) according to CLSI breakpoints or Epidemiological CutoffValues (ECV) as appropriate. EA and CA were determined for the antifungals Amphotericin B, Caspofungin, Micafungin, Flucytosine, Fluconazole and Voriconazole. Vitek 2 AST YS08 does not provide results for Candida glabrata against Fluconazole and Voriconazole, nor for Candida krusei against Fluconazole. There is no CLSI breakpoint or ECV for Flucystosine, therefore no CA was calculated.
Fluconazole (n=39) EA 77%, CA 90%, Voriconazole (n=47) EA 79%, CA 66%, Caspofungin (n=62) EA 100%, CA 82%, Micafungin (n=54) EA 100%, CA 100%, Amphotericin B (n=67) EA 100%, CA 100%, Flucytosine (n=68) EA 99%.
In this study skewed for resistant Candida isolates, EA and CA for Vitek 2 AST YS08 and Sensititre YeastONE were suboptimal. More validation data needs to be obtained for the Vitek 2 AST YS08.