Evaluation of Etest Method for Determining Fluconazole and Voriconazole MICs for 279 Clinical Isolates of Candida Species Infrequently Isolated from Blood

Abstract

The performance of Etest in fluconazole and voriconazole testing of 279 isolates of uncommon Candida spp. was assessed in comparison with the National Committee for Clinical Laboratory Standards (NCCLS)-approved standard broth microdilution (BMD) method. The NCCLS method employed RPMI 1640 broth medium, and MICs were read after incubation for 48 h at 35°C. Etest MICs were determined with RPMI agar containing 2% glucose and were read after incubation for 48 h at 35°C. The isolates include Candida krusei, C. lusitaniae, C. guilliermondii, C. kefyr, C. rugosa, C. lipolytica, C. pelliculosa, C. dubliniensis, C. famata, C. zeylanoides, C. inconspicua, and C. norvegensis. Overall agreement between Etest and BMD MICs was 96% for fluconazole and 95% for voriconazole. Where a discrepancy was observed between Etest and the reference method, the Etest tended to give lower values with both fluconazole and voriconazole. The Etest method using RPMI agar appears to be a useful method for determining fluconazole and voriconazole susceptibilities of uncommon species of Candida.The Etest stable agar gradient MIC method (AB BIODISK, Solna, Sweden) has been shown to be useful in testing Candida spp. against a variety of antifungal agents, including fluconazole and voriconazole (1,3,9,11,12,14,16,17,22,24). The species of Candida tested in these studies generally represent those most commonly isolated from clinical sources and are dominated by Candida albicans, C. glabrata, C. parapsilosis, and C. tropicalis, which account for 95 to 97% of all clinical isolates of Candida spp. (8,13,15,18). Thus, although Etest has been validated for the four most common species of Candida, the evidence supporting its use in testing the less common species is lacking.Among the approximately 17 species of Candida reported to cause bloodstream infections (BSI) (8), 12 or 13 of these species account for less than 5% of all Candida BSI (19). These rare species include among others, C. krusei, C. lusitaniae, C. guilliermondii, C. kefyr, C. rugosa, and C. dubliniensis, several of which may pose problems with antifungal resistance and nosocomial spread (4,5,7,23,26). Although less common than C. albicans, C. glabrata, C. parapsilosis, and C. tropicalis, these species may pose difficult management problems for individual patients, which may benefit from the application of antifungal susceptibility testing (21). Given the use of Etest for antifungal susceptibility testing of the common Candida spp. causing BSI, it is reasonable to validate its use for testing systemically active agents, such as fluconazole and voriconazole, against these less common species as well.The purpose of the present study is to expand the Etest database for fluconazole and voriconazole by testing an international collection of 279 clinical BSI isolates of 12 uncommon species of Candida obtained from 68 different locations in 26 nations. The fluconazole and voriconazole MICs determined by Etest are compared to MICs determined by the National Committee for Clinical Laboratory Standard...

In Vitro Antifungal Susceptibility of Cryptococcus gattii

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Isolation ofCandida famatafrom a Patient with Acute Zonal Occult Outer Retinopathy

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