Comparison of the VITEK 2 antifungal susceptibility system with Etest using clinical isolates of Candida species.

Background: Candida species are part of the normal human microbiota. However, in recent years, nosocomial bloodstream Candida infections have emerged as a significant problem ranking the fourth common cause of fungemia in intensive care units. Although microdilution methods are the ones recommended for susceptibility testing, they are difficult to undertake in the clinical practice. Thus, an automated commercially available test is ideal.

Aims: To compare minimum inhibitory concentrations (MICs) obtained with the recently introduced Vitek 2 yeast susceptibility system card (AST-YS01) with Etest.

Methods: 263 clinical Candida isolates representing six species were included in the study. Categorical agreements (CA) were assessed as described elsewhere.

Results: Irrespective of the Candida species tested, the overall CA between Vitek 2 and Etest ranged between 66.7% and 100%. In general, Etest yielded lower MICs than Vitek 2. For Candida albicans, the CA between Vitek 2 and Etest was >95% for amphotericin B, voriconazole and flucytosine, but only 89% for fluconazole. With respect to Candida glabrata, the CA was between 97% and 100%. The major errors were with Candida krusei and flucytosine and Candida kefyr and amphotericin B. Candida tropicalis susceptibility for fluconazole by Vitek 2 reported more SDD and resistant strains than Etest. Candida parapsilosis showed 100% CA against all the four antifungals tested. No very major errors were detected between the two methods.

Conclusions: Vitek 2 provided comparable results to Etest with quick turnaround for the testing of Candida species susceptibilities.