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Journal of Clinical Microbiology, April 2001, p. 1422-1428, Vol. 39, No. 4
0095-1137/01/$04.00+0   DOI: 10.1128/JCM.39.4.1422-1428.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Fluconazole and Voriconazole Multidisk Testing of Candida Species for Disk Test Calibration and MIC Estimation

Göran Kronvall* and Inga Karlsson

Department of Microbiology and Tumor Biology---MTC, Clinical Microbiology, Karolinska Institute, Karolinska Hospital, Stockholm SE-17176, Sweden

Received 11 September 2000/Returned for modification 29 December 2000/Accepted 26 January 2001

Fluconazole and voriconazole MICs were determined for 114 clinical Candida isolates, including isolates of Candida albicans, Candida glabrata, Candida krusei, Candida lusitaniae, Candida parapsilosis, and Candida tropicalis. All strains were susceptible to voriconazole, and most strains were also susceptible to fluconazole, with the exception of C. glabrata and C. krusei, the latter being fully fluconazole resistant. Single-strain regression analysis (SRA) was applied to 54 strains, including American Type Culture Collection reference strains. The regression lines obtained were markedly different for the different Candida species. Using an MIC limit of susceptibility to fluconazole of <= 8 µg/ml, according to NCCLS standards, the zone breakpoint for susceptibility for the 25-µg fluconazole disk was calculated to be >= 18 mm for C. albicans and >= 22 mm for C. glabrata and C. krusei. SRA results for voriconazole were used to estimate an optimal disk content according to rational criteria. A 5-µg disk content of voriconazole gave measurable zones for a tentative resistance limit of 4 µg/ml, whereas a 2.5-µg disk gave zones at the same MIC level for only three of the species. A novel SRA modification, multidisk testing, was also applied to the two major species, C. albicans and C. glabrata, and the MIC estimates were compared with the true MICs for the isolates. There was a significant correlation between the two measurements. Our results show that disk diffusion methods might be useful for azole testing of Candida isolates. The method can be calibrated using SRA. Multidisk testing gives direct estimations of the MICs for the isolates.


* Corresponding author. Mailing address: Clinical Microbiology---MTC, Karolinska Hospital L2:02, Stockholm SE-17176, Sweden. Phone: 46-8-51774910. Fax: 46-8-308099. E-mail address: goran.kronvall{at}ks.se.


Journal of Clinical Microbiology, April 2001, p. 1422-1428, Vol. 39, No. 4
0095-1137/01/$04.00+0   DOI: 10.1128/JCM.39.4.1422-1428.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.



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