In vitro susceptibilities of clinical yeast isolates to three antifungal agents determined by the microdilution method |
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Authors: | M A Pfaller A L Barry |
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Institution: | (1) Department of Pathology, 273 MRC, University of Iowa College of Medicine, 52242 Iowa City, IA, USA;(2) The Clinical Microbiology Institute, Tualatin, Oregon, USA |
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Abstract: | A comparative evaluation of the in vitro susceptibilities of 597 clinical yeast isolates to amphotericin B, fluconazole, and 5-fluorocytosine (5FC) was conducted. The broth macrodilution reference method of the National Committee for Clinical Laboratory Standards (NCCLS, M27-P) was adapted to the microdilution method. Microdilution endpoints for amphotericin B were scored as the lowest concentration in which a score of 0 (complete absence of growth) was observed and for 5FC and fluconazole as the lowest concentration in which a score of 2 (prominent decrease in turbidity; MIC-2) was observed compared to the growth control. The MIC values were read after 24 and 48 h incubation. A broad range of MIC values was observed with each antifungal agent. Amphotericin B was very active (MIC901.0 µg/ml) against all of the yeast isolates with the exception ofC. lusitaniae (MIC902.0 µg/ml). Fluconazole was most active againstC. parapsilosis (MIC90 of 1.0 µg/ml) and least active againstC. krusei (MIC90 of 32 µg/ml). 5FC was most active againstC. albicans, C. parapsilosis, C. tropicalis, andT. glabrata (MIC901.0 µg/ml) and was least active againstC. krusei andC. lusitaniae (MIC9016 µg/ml). These data indicate that the microdilution method, performed in accordance with M27-P, provides a means of testing larger numbers of yeast isolates against an array of antifungal agents and allows this to be accomplished in a reproducible and standardized manner. Given these results, it appears that the microdilution method may be a useful alternative to the macrodilution reference method for susceptibility testing of yeasts. |
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Keywords: | Antifungal Microdilution Yeasts |
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