Background: The aims of this study were to evaluate the colorimetric antifungal susceptibility test to fluconazole using 2,3-diphenyl-5-thienyl-(2)-tetrazolium chloride (STC) for various Candida species isolated from clinical specimens and to compare the results with those of the CLSI M27-A2 standard method.

Methods: The fluconazole MICs for 204 clinical Candida isolates consisting of 100 C. albicans, 45 C. glabrata, 28 C. tropicalis, 22 C. parapsilosis, and 9 other Candida species were determined by the CLSI and STC colorimetric methods.

Results: All 204 Candida strains were grown on the growth control wells of CLSI standard plates, but 26 Candida strains (6 C. albicans and 20 C. tropicalis) were not grown on those containing STC. Therefore, those 26 Candida strains were excluded from the comparison of MICs in this report. Overall, the STC visual and spectrophotometric readings of fluconazole MICs showed 96.1% (N=171) and 89.9% (N=160) accordance with those obtained by the CLSI standard method within 2 dilutions, respectively. The STC visual reading of C. albicans showed 76.6, 92.6, and 95.8% accordance with the CLSI standard method within 1, 2, and 3 dilutions, respectively. The agreement between the two endpoint determinations of the STC colorimetric method (visual and spectrophotometric readings) was excellent, with 170 of the 178 MICs within 2 dilutions.

Conclusion: The STC colorimetric method to determine the MIC for Candida species except C. tropicalis showed high levels of agreement with CLSI method. And also, it is useful with objective and easy interpretation. (Korean J Clin Microbiol 2007;10:90-95)