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 MIC 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 agreement, 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.
Wanger
A
A
Department of Pathology, University of Texas Medical School, Houston, USA.
Mills
K
K
Nelson
P W
PW
Rex
J H
JH
D000666:Amphotericin B / Q000494:pharmacology*; D000890:Anti-Infective Agents / Q000494:pharmacology; D000935:Antifungal Agents / Q000494:pharmacology*; D002175:Candida / Q000187:drug effects*; D003470:Culture Media; D004352:Drug Resistance, Microbial; D015725:Fluconazole / Q000494:pharmacology; D024841:Fluoroquinolones; D008826:Microbial Sensitivity Tests / Q000379:methods* / Q000592:standards; D011786:Quality Control
D000890:Anti-Infective Agents; D000935:Antifungal Agents; D003470:Culture Media; D024841:Fluoroquinolones; D000666:Amphotericin B; D015725:Fluconazole