Evaluation of Etest Method for Determining Posaconazole MICs for 314 Clinical Isolates of Candida Species

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Abstract
The performance of the Etest for posaconazole (SCH 56592) susceptibility testing of 314 isolates of Candida spp. was assessed against the National Committee for Clinical Laboratory Standards (NCCLS) microdilution broth method. The NCCLS method employed RPMI 1640 broth medium, and MICs were read after incubation for 48 h at 35°C. MICs were determined by Etest for all 314 isolates with RPMI agar containing 2% glucose (RPG agar) and were read after incubation for 48 h at 35°C. The Candida isolates included C. albicans ( n = 174), C. glabrata ( n = 57), C. tropicalis ( n = 31), C. parapsilosis ( n = 39), C. krusei ( n = 5), C. guilliermondii ( n = 6), and C. lusitaniae ( n = 2). The Etest results correlated well with reference MICs. Overall agreement was 95%, and agreements for individual species were as follows: C. krusei , 100%; C. albicans , 98%; C. tropicalis , 97%; C. glabrata , 93%; C. parapsilosis , 85%; C. guilliermondii , 83%; and C. lusitaniae , 50%. The problem of trailing end points was minimized with RPG agar, and good agreement with broth dilution MICs was obtained when discernible growth within an established ellipse was ignored. The Etest method using RPG agar appears to be a useful method for determining posaconazole susceptibilities of Candida species.