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Journal of Clinical Microbiology, Jul 1996, 1691-1693, Vol 34, No. 7
MA Pfaller, SA Messer, A Bolmstrom, FC Odds and JH Rex
A multicenter study was performed to establish the interlaboratory
reproducibility of Etest, to provide an additional comparison of Etest MICs
with reference broth macrodilution MICs, and to develop some tentative
quality control (QC) guidelines for using Etest for antifungal
susceptibility testing of Candida spp. Two QC strains, Candida parapsilosis
ATCC 22019 and Candida krusei ATCC 6258, were tested by Etest against
amphotericin B, fluconazole, flucytosine, itraconazole, and ketoconazole in
each of four laboratories. The QC strains were tested 20 times each against
the five antifungal agents by using a common lot of RPMI agar. A total of
80 MICs per drug per strain were generated during the study. Overall, 98 to
100% of the MICs fell within a 3 log2 dilution range for the respective
yeast-antifungal agent combinations. The level of agreement of Etest MICs
with broth macrodilution MICs was 86 to 100% with amphotericin B (C. krusei
and C. parapsilosis), itraconazole (C. krusei and C. parapsilosis),
flucytosine (C. parapsilosis), and fluconazole (C. parapsilosis). A lower
level of agreement was observed with ketoconazole (C. krusei and C.
parapsilosis). Although all participants reported identical Etest MICs, the
MICs of flucytosine and fluconazole when tested against C. krusei fell well
above the upper limits of the reference range for this strain. The
tentative QC limits for the two QC strains and five antifungal agents when
tested by the Etest methodology are the same as the QC limits when tested
by the reference broth macrodilution method for amphotericin B and C.
krusei, itraconazole and C. krusei, flucytosine and C. parapsilosis,
fluconazole and C. parapsilosis, and itraconazole and C. parapsilosis. The
Etest QC ranges are 1 dilution broader (4-dilution range) than the
reference macrodilution method QC ranges for ketoconazole and C. krusei,
amphotericin B and C. parapsilosis, and ketoconazole and C. parapsilosis.
Copyright © 1996 by the American Society for Microbiology. All rights reserved.
Multisite reproducibility of the Etest MIC method for antifungal susceptibility testing of yeast isolates
Department of Pathology, University of Iowa College of Medicine, Iowa City 52242, USA.
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