Multicenter Comparison of the Etest and EUCAST Methods for Antifungal Susceptibility Testing of Candida Isolates to Micafungin

Abstract

In vitro susceptibility of 933 Candida isolates, from 16 French hospitals, to micafungin was determined using the Etest in each center. All isolates were then sent to a single center for determination of MICs by the EUCAST reference method. Overall essential agreement between the two tests was 98.5% at ؎2 log 2 dilutions and 90.2% at ؎1 log 2 dilutions. Categorical agreement was 98.2%. The Etest is a valuable alternative to EUCAST for the routine determination of micafungin MICs in medical mycology laboratories. The echinocandin antifungal drug micafungin is highly effective in vitro against most Candida species (1-3). Micafungin is now widely used for prophylaxis and treatment of invasive candidiasis (IC) (4,5). During the last decade, acquired resistance of various Candida species to echinocandins has emerged worldwide, including in France, and may become an important issue in the therapeutic management of IC (6-10).In vitro antifungal susceptibility testing is currently recommended to detect resistance in Candida species and to guide antifungal treatment (6, 11). Microdilution broth methods such as those published by EUCAST and CLSI are the reference methods for antifungal susceptibility testing. Nevertheless, because these reference methods are labor-intensive and time-consuming, most clinical microbiology laboratories use commercial methods, such as the Etest, for routine determination of MICs. It is therefore essential to evaluate these commercial tests and to determine their ability to give MIC values that agree with those from the reference methods. With this aim, a prospective, multicenter French study was performed to compare the EUCAST and Etest methods for micafungin susceptibility testing of a large panel of clinical isolates of different Candida species.(This study was presented in part at the 25th European Congress of Clinical Microbiology and Infectious Diseases [ECCMID], Copenhagen, Denmark, 25 to 28 April 2015.) Sixteen centers (6 in the Paris area and 10 elsewhere across France) participated in the study. Over a 2-month period, each center was asked to test 64 Candida isolates, from any clinical sample, of the following species: 10 isolates of each of the six most common pathogenic species (Candida albicans, C. glabrata, C. tropicalis, C. parapsilosis, C. kefyr, and C. krusei) and four isolates belonging to other Candida species. Species identification was performed in each center according to the currently recommended phenotypic methods (12). Micafungin susceptibility testing was performed using the Etest (bioMérieux, Marcy l'Etoile, France), according to the manufacturer's instructions. Candida isolates were then sent to a single center for MIC determination by the EUCAST reference method (13). C. krusei ATCC 6258 and C. parapsilosis ATCC 22019 were included as quality control strains (14). For comparison purposes, Etest MICs were increased to the glabrata, and C. parapsilosis isolates were considered susceptible or resistant to micafungin when MICs were Յ0.016 or Ͼ0.016 g/ml, Յ0.03 or ...

Multicenter Study of Method-Dependent Epidemiological Cutoff Values for Detection of Resistance in Candida spp. and Aspergillus spp. to Amphotericin B and Echinocandins for the Etest Agar Diffusion Method

“…The highest amphotericin B modes were for C. krusei (1 g/ml), A. flavus SC (2 g/ml), and A. terreus SC (4 g/ml) ( Tables 2 and 3). In general, similar Etest data have been previously published (34)(35)(36)(37)(38)(39)(40)(41), but as observed in prior ECV studies, our MIC ranges tended to be wider, especially for Candida spp. versus anidulafungin and micafungin.…”

“…Although BPs are not available for most fungal species-agent combinations, CLSI ECVs have been established for more fungal species (both prevalent and less common) based solely on reference in vitro data (10,11,18). The Etest method has been extensively evaluated for testing both yeasts and molds and the antifungal agents included in the present study (34)(35)(36)(37)(38)(39)(40)(41) to estimate essential and categorical agreement with reference methods or the potential Etest's superior value as a predictor of antifungal resistance. Given that the Etest relies on CLSI BPs for clinical interpretation of results, method-dependent Etest ECVs could be useful in the clinical setting.…”

Antifungal drug susceptibility, molecular basis of resistance to echinocandins and molecular epidemiology of fluconazole resistance among clinical Candida glabrata isolates in Kuwait

“…Espinel-Ingroff et al 34 , reported an essential agreement of 95% and a categorical agreement of 97% between Etest and CLSI BMD method while Marcos-Zambrano et al 35 , reported an essential agreement of 90% and a categorical agreement of >90% between Etest and EUCAST BMD method. Bougnoux et al 36 , in a recent study based on 933 Candida species isolates (including 152 C. glabrata isolates) reported an essential agreement of 98.5% and a categorical agreement of 98.2% between Etest and EUCAST BMD method. Similar to these studies, our data also support that Etest is an easy and reliable method for routine AST of clinical C. glabrata isolates to micafungin.…”

Fluconazole and Echinocandin Resistance of Candida glabrata Correlates Better with Antifungal Drug Exposure Rather than with MSH2 Mutator Genotype in a French Cohort of Patients Harboring Low Rates of Resistance

“…In addition, high micafungin MIC results have been shown to correlate with the occurrence of FKS mutations, which is also the case for high caspofungin MICs (Pham et al, 2014). We used Etest® for the echinocandin susceptibility testing since it is considered a valuable alternative to the EUCAST broth microdilution method for routine susceptibility testing of micafungin in C. glabrata isolates, with categorical agreement of 96.7% (Bougnoux et al, 2016)…”