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Journal of Clinical Microbiology, April 2001, p. 1328-1333, Vol. 39, No. 4
Institute of Medical
Engineering,1 Department of
Statistics,2 and Department of Medical
Technology, College of Medicine,5
National Cheng Kung University, Division of Clinical
Microbiology, Department of Pathology, National Cheng Kung
University Hospital,3 and Department of
Clinical Pathology, Linko Medical Center, Chang Gung Memorial
Hospital,4 Tainan 701, Taiwan, Republic of China
Received 8 August 2000/Returned for modification 25 September
2000/Accepted 28 January 2001
The performance of the Etest (AB BIODISK, Solna, Sweden) for direct
antifungal susceptibility testing of yeasts in positive blood cultures
was compared with that of the macrodilution method for determining the
MICs of five antifungal agents. Culture broths with blood from bottles
positive for yeasts were inoculated directly onto plates for
susceptibility testing with the Etest, and the MICs were read after 24 and 48 h of incubation. A total of 141 positive blood cultures (72 cultures of Candida albicans, 31 of Candida
tropicalis, 14 of Candida glabrata, 11 of
Candida parapsilosis, 3 of Candida krusei, and
3 of Cryptococcus neoformans, 4 miscellaneous yeast
species, and 3 mixed cultures) were tested, and the rates of MIC
agreement (±1 log2 dilution) between the direct Etest (at 24 and 48 h, respectively) and macrodilution methods were as
follows: amphotericin B, 81.8 and 93.5%; flucytosine, 84.8 and 87.7%;
fluconazole, 89.4 and 85.5%; itraconazole, 69.7 and 63.8%;
ketoconazole, 87.9 and 79.0%. By a large-sample t test,
the difference in log2 dilution between the direct Etest
and the macrodilution method was found to be small (P < 0.05). The lone exceptions were ketoconazole at 48 h of
incubation and itraconazole at both 24 and 48 h of incubation
(P > 0.05). By Tukey's multiple comparisons, the
difference between the direct Etest (48 h) and reference methods among
different species was found to be less than 1 log2
dilution. When the MICs were translated into interpretive
susceptibility, the minor errors caused by the direct Etest (at 24 and
48 h, respectively) were as follows: flucytosine, 2.3 and 1.4%;
fluconazole, 3.0 and 3.6%; itraconazole, 21.2 and 21.3%. Itraconazole
also produced an additional 3.0 and 3.6% major errors as determined by
the direct Etest at 24 and 48 h, respectively. It was concluded
that, except for itraconazole, the Etest method was feasible for direct
susceptibility testing of blood cultures positive for yeasts. The
method is simple, and the results could be read between 24 and 48 h after direct inoculation, whenever the inhibition zones were discernible.
0095-1137/01/$04.00+0 DOI: 10.1128/JCM.39.4.1328-1333.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Evaluation of Etest for Direct Antifungal
Susceptibility Testing of Yeasts in Positive Blood Cultures
*
Corresponding author. Mailing address: Department of
Medical Technology, College of Medicine, National Cheng Kung
University, 1 University Rd., Tainan 701, Taiwan, Republic of
China. Phone: 886-6-2353535, ext. 5790. Fax: 886-6-2363956. E-mail:
tsungcha{at}mail.ncku.edu.tw.
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