Candidosis is a fungal infection caused by Candida spp. in immunocompromised patients. Early antifungal treatment has been shown to significantly reduce mortality and morbidity. Choice of appropriate therapy depends on antifungal susceptibility testing of yeasts, which is mostly performed with commercially avaible tests. The best interlaboratory comparability is provided by reference dilution methods, such as EUCAST microdilution. The result of microdilution are the minimal inhibitory concentrations (MICs) of antimycotics. On the basis of MIC, the isolates can be interpreted as sensitive, intermediate or resistant. In our study a commercial microtiter plate (Merlin Diagnostika, Germany) with lyophilized antimycotics was used. Susceptibility was determined by two microdilution methods modified for EUCAST. MIC was determined visually with and without added colour indicator and spectrophotometrically at wavelengths of 450 nm and 492 nm. We compared our MIC values with reference values. The most suitable method of determining MIC depends on the combination of yeast isolate and antimycotic. We have determed that low echinocandin MICs could be corrected using correction factor 2. The categorical agreement between visual determination of azole MICs and reference values was low. Modified EUCAST methods are not suitable for routine mycology laboratories due to insufficient agreement of results compared to the reference laboratory values. The exception is amphotericin B.
|
