Ma. Pfaller et al., MULTISITE REPRODUCIBILITY OF THE ETEST MIC METHOD FOR ANTIFUNGAL SUSCEPTIBILITY TESTING OF YEAST ISOLATES, Journal of clinical microbiology, 34(7), 1996, pp. 1691-1693
A multicenter study was pel formed to establish the interlaboratory re
producibility of Etest, to provide an additional comparison of Etest M
ICs with reference broth macrodilution MICs, and to develop some tenta
tive quality control (QC) guidelines for using Etest for antifungal su
sceptibility testing of Candida spp. Two QC strains, Candida parapsilo
sis ATCC 22019 and Candida krusei ATCC 6258, were tested by Etest agai
nst amphotericin B, fluconazole, flucytosine, itraconazole, and ketoco
nazole in each of four laboratories. The QC strains were tested 20 tim
es each against the five antifungal agents by using a common lot of RP
MI 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 log, diluti
on range for the respective yeast-antifungal agent combinations. The l
evel of agreement of Etest MICs with broth macrodilution MICs was 86 t
o 100% with amphotericin B (C. krusei and C. parapsilosis), itraconazo
le (C. krusei and C. parapsilosis), flucytosine (C. parapsilosis), and
fluconazole (C. parapsilosis). A lower level of agreement was observe
d with ketoconazole (C. krusei and C. parapsilosis), Although all part
icipants reported identical Etest MICs, the MICs of flucytosine and fl
uconazole when tested against C. krusei fell well above the upper limi
ts of the reference range for this strain. The tentative QC limits for
the two QC strains and five antifungal agents when tested by the Etes
t methodology are the same as the QC limits when tested by the referen
ce broth macrodilution method for amphotericin B and C. krusei, itraco
nazole and C. krusei, flucytosine and C. parapsilosis, fluconazole and
C. parapsilosis, and itraconazole and C. parapsilosis. The Etest QC r
anges are 1 dilution broader (4-dilution range) than the reference mac
rodilution method QC ranges for ketoconazole and C. krusei, amphoteric
in B and C. parapsilosis, and ketoconazole and C. parapsilosis.