COMPARISON OF ETEST AND NATIONAL-COMMITTEE-FOR-CLINICAL-LABORATORY-STANDARDS BROTH MACRODILUTION METHOD FOR ANTIFUNGAL SUSCEPTIBILITY TESTING - ENHANCED ABILITY TO DETECT AMPHOTERICIN B-RESISTANT CANDIDA ISOLATES

The National Committee for Clinical Laboratory Standards (NCCLS) proposed macrobroth reference method (M27P) for susceptibility testing of yeasts is technically difficult, We evaluated Etest, a simple agar-based MTC methodology, as a possible alternative. In studies of six yeast quality control strains, Etest yielded results identical to those obtained by the NCCLS reference method for both amphotericin B and fluconazole. In studies of 91 clinical Candida isolates, agreement +/- 2 dilutions between the two methods was 95% for fluconazole with phosphate-buffered RPMI 1640 agar and 96 to 97% for amphotericin B with either MOPS (morpholinepropanesulfonic acid)-buffered RPMI 1640 agar or antibiotic medium 3 agar. While the two methods had excellent general agrement, testing of a collection of amphotericin B-resistant isolates demonstrated that, unlike the NCCLS reference method, Etest readily identified the resistant isolates and could do so with a defined medium. Etest is equivalent to the NCCLS proposed method for susceptibility testing of yeasts and superior in its ability to detect amphotericin B resistance.