SUSCEPTIBILITY TESTING OF YEASTS AGAINST FLUCONAZOLE - COMPARISON OF THE ETEST METHOD WITH MICRODILUTION AND AGAR DILUTION

In bacteriology, the Etest has a broad field of application in bacteri ology and is recently available for the antimycotics fluconazole and i traconazole. By means of the presence of gradient concentrations of th e active substance on the carrier material, it is possible to obtain r eproducible MICs of the antimycotic substances. The results of suscept ibility testing of 326 clincal yeast isolates with the Etest were comp ared to those MICs obtained by microdilution and agar dilution. A 100% concordance of the MIC markers (mode-, MIC50- and MIC90-value, standa rd deviation of the mean log(2)-MIC-dilution steps) was given when com pared by a +/- 1 MIC-dilution step range with microdilution and by +/- 2 MIC-dilution steps with agar dilution; species dependent all strain s were within 2 x standard deviation of the individual MIC-mean of the species. By comparison of the individual MIC-values maximum differenc es of +/- 6 MIC-dilution steps were obtained, where 70% of all results were within +/- 2 MIC-dilution steps, and more than 92% of all strain s were within +/- 3 MIC-dilution steps. The Pearson's correlation coef ficients show a good agreement of the Etest with microdilution (r = 0, 92) resp., agar dilution (r = 0,88) demonstrate, however, clearly insu fficient correlations (r < 0,65) to the reference methods, for species with difficult to read Etest inhibition zones (e.g., Candida glabrata , Candida krusei, Candida parapsilosis). The differences between the p roposed test methods recommended by the NCCLS and the working group '' Clinical Mycology'' of the German Speaking Mycological Society (AG-KMY K) are tabled.