Comparison of a new commercial colorimetric microdilution method with a standard method for in-vitro susceptibility testing of Candida spp. and Cryptococcus neoformans

Abstract

The Sensititre Yeast One method (AccuMed International Ltd, East Grinstead, UK) is a microplate-based procedure that incorporates an oxidation-reduction indicator, Alamar Blue, for the in-vitro testing of five antifungal agents (amphotericin B, fluconazole, itraconazole, ketoconazole and flucytosine). We compared this colorimetric method with a standard broth microdilution test, performed according to US National Committee for Clinical Laboratory Standards document M27-A guidelines, for determining the in-vitro susceptibilities of 180 isolates of Candida spp. (50 Candida albicans, 50 Candida glabrata, ten Candida kefyr, 20 Candida krusei, ten Candida lusitaniae, 20 Candida parapsilosis and 20 Candida tropicalis) and 20 isolates of Cryptococcus neoformans. The overall agreement between the results of the two methods (colorimetric MICs within +/- two log2 dilutions of standard MICs) were 99% for amphotericin B, 96.5% for flucytosine, 93% for itraconazole, 91.5% for fluconazole and 85.5% for ketoconazole. The overall levels of agreement between the two methods were > or = 94% for six of the eight species tested, the exceptions being C. neoformans and C. tropicalis where the overall agreement was 89% and 80% respectively. The poorest agreement between the results for individual agents was seen with C. tropicalis and the three azole agents (60-75% of colorimetric MICs within +/- two log2 dilutions of standard MICs), and C. neoformans for ketoconazole (50%). The Yeast One method appears to be a suitable alternative procedure for routine antifungal susceptibility testing of Candida spp. and C. neoformans.

Trends in Antifungal Susceptibility among Swedish Candida Species Bloodstream Isolates from 1994 to 1998: Comparison of the E-test and the Sensititre YeastOne Colorimetric Antifungal Panel with the NCCLS M27-A Reference Method

“…With the advent of the NCCLS reference method for antifungal susceptibility testing, it is now possible to compare and evaluate alternative, easierto-perform methods (6). The commercially available E-test and Sensititre YeastOne antifungal panel have both demonstrated good agreement with the NCCLS method in previous studies (2,3,4,16).…”

“…The performance of both the E-test and the YeastOne panel was comparable to that of the NCCLS reference for C. albicans (2,3,5). In general, the E-test tended to give higher MIC 50 s of flucytosine and itraconazole among non-C. albicans Candida isolates.…”

Evaluation of Etest for Direct Antifungal Susceptibility Testing of Yeasts in Positive Blood Cultures

“…Although the NCCLS M27-A reference method remains the standard by which all other methods are judged, it is impossible for a modest-size laboratory to perform the test on a routine basis. There have been many alternatives to the MD method developed over the past several years, including the broth colorimetric microdilution technique (7,23,33), flow cytometry (37), and MIC diffusion strips (Etest) (6,26,32). Of these, the Etest seems more adaptable for the routine workload, and, in several reports, results have been comparable to those by the MD method.…”

Multicenter Comparative Evaluation of Six Commercial Systems and the National Committee for Clinical Laboratory Standards M27-A Broth Microdilution Method for Fluconazole Susceptibility Testing of Candida Species

“…It provides validated breakpoints for interpretive classification of in vitro fluconazole, flucytosine, and itraconazole susceptibility data. Despite the advantages, however, many clinical laboratories prefer to use commercially available products (1,4,5,9,10,14,17), which claim to be easier and more rapid alternatives to the method recommended by the NCCLS. However, some of these products, at least in Italy, can be marketed without prior demonstration of their reliability.…”