Comparison of 24-Hour and 48-Hour Voriconazole MICs as Determined by the Clinical and Laboratory Standards Institute Broth Microdilution Method (M27-A3 Document) in Three Laboratories: Results Obtained with 2,162 Clinical Isolates of Candida spp. and Other Yeasts

Abstract

We evaluated the performance of the 24-h broth microdilution voriconazole MIC by obtaining MICs for 2,162 clinical isolates of Candida spp. and other yeasts; the 24-h results were compared to 48-h reference MICs to assess essential, as well as categorical, agreement. Although the overall essential agreement was 88.6%, it ranged from 96.4 to 100% for 6 of the 11 species or groups of yeasts tested. The overall categorical agreement was 93.2%, and it was above 90% for eight species. However, unacceptable percentages of very major errors (false susceptibility) were observed for Candida albicans (2.7%), C. glabrata (4.1%), C. tropicalis (9.7%), and other less common yeast species (9.8%). Since it is essential to identify potentially resistant isolates and breakpoints are based on 48-h MICs, it appears that the 24-h MIC is not as clinically useful as the 48-h reference MIC. However, further characterization of these falsely susceptible MICs for three of the four common Candida spp. is needed to understand whether these errors are due to trailing misinterpretation or if the 48-h incubation is required to detect voriconazole resistance. Either in vivo versus in vitro correlations or the determination of resistance mechanisms should be investigated.Candida spp. and Aspergillus spp. are responsible for the majority (80 to 90%) of fungal infections. During the last several years, new antifungal agents (echinocandins and triazoles) have been licensed for the systemic treatment of fungal infections. Among the triazoles, voriconazole is available for the oral or intravenous treatment of mold and yeast infections (e.g., primary treatment of invasive candidiasis, including candidemia, in neutropenic and nonneutropenic patients). These events have underscored the need for testing the antifungal susceptibilities of fungal pathogens to these agents. The Clinical and Laboratory Standards Institute (CLSI) has developed reference methods (CLSI M27-A3 and M44-A documents) for antifungal susceptibility testing of Candida spp. and Cryptococcus neoformans (3,5,6). In addition to the guidelines for testing voriconazole, the CLSI has established interpretive breakpoints for this agent versus Candida spp. (5,6,19). These microdilution MIC breakpoints were based on the determination of voriconazole MICs after 48 h of incubation. However, most common Candida spp. have suitable growth for MIC determination at 24 h; a shorter incubation time is more efficient and practical for use in the clinical laboratory and is currently used to determine endpoints for the echinocandins, amphotericin B, and fluconazole. The interlaboratory reproducibility of the 24-h voriconazole result, as well as the categorical agreement between 24-and 48-h MICs were previously addressed in a collaborative study for a small number of Candida isolates (8). The purpose of the present study was to further evaluate the suitability of CLSI 24 h voriconazole MIC results with 2,162 clinical isolates of Candida and other yeast species. The evaluation involved (i) the compatibilit...

Progress in Antifungal Susceptibility Testing of Candida spp. by Use of Clinical and Laboratory Standards Institute Broth Microdilution Methods, 2010 to 2012

“…The vast majority of Candida species achieve sufficient growth within 24 h of incubation to allow MIC testing using the CLSI BMD method (20)(21)(22)61). Given that a shorter duration of incubation avoids the potentially confounding effect of trailing growth on 48-h MICs (7,61,80,84), is more efficient and practical for use in the clinical laboratory (22,61), and provides useful information sooner (30,48,54), attention has been focused on the validation of 24-h MIC determinations for antifungal agents and Candida.…”

“…Given that a shorter duration of incubation avoids the potentially confounding effect of trailing growth on 48-h MICs (7,61,80,84), is more efficient and practical for use in the clinical laboratory (22,61), and provides useful information sooner (30,48,54), attention has been focused on the validation of 24-h MIC determinations for antifungal agents and Candida. Investigators have used previously gathered Candida MIC data to evaluate the essential agreement (EA; agreement within Ϯ2 log 2 dilutions) and categorical agreement (CA) between MIC values determined at 24-h and 48-h incubation for amphotericin B, fluconazole, flucytosine, itraconazole, posaconazole, and voriconazole (39,50,61,63,67,72,73,76).…”

Rapid Antifungal Susceptibility Determination for Yeast Isolates by Use of Etest Performed Directly on Blood Samples from Patients with Fungemia

“…ETsd was also compared with CLSI M27-A3. Agreement between the methods was considered to be essential when the log 2 MIC measured by each method was within Ϯ2 or fewer than 2-fold dilutions of the next one (8,13,21).…”

Comparative Evaluation of the Vitek 2 Yeast Susceptibility Test and CLSI Broth Microdilution Reference Method for Testing Antifungal Susceptibility of Invasive Fungal Isolates in Italy: the GISIA3 Study

“…However, both of these methods are time-consuming and clinical microbiological laboratory personnel may be unfamiliar with the methodologies (3,6,11,12,14,20). Commercially available methods demonstrate variable performance compared with the performance of reference methods; two commercial assays have been approved by the U.S. Food and Drug Administration (FDA) for AFST of fungi with several antifungal agents: Etest (bioMérieux SA, Marcy l'Etoile, France) and the Sensititre YeastOne system (Trek Diagnostic Systems Ltd., East Grinstead, England).…”