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Journal of Clinical Microbiology, September 2000, p. 3359-3361, Vol. 38, No. 9
0095-1137/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
In Vitro Susceptibility Testing of Filamentous Fungi:
Comparison of Etest and Reference Microdilution Methods for
Determining Itraconazole MICs
M. A.
Pfaller,1,*
S. A.
Messer,1
K.
Mills,2 and
A.
Bolmström2
Department of Pathology, University of Iowa
College of Medicine, Iowa City, Iowa,1 and
AB BIODISK, Solna, Sweden2
Received 26 April 2000/Returned for modification 13 June
2000/Accepted 12 July 2000
The performance of the Etest for itraconazole susceptibility
testing of 50 isolates of filamentous fungi was assessed in comparison with the National Committee for Clinical Laboratory Standards (NCCLS)
proposed standard microdilution broth method. The NCCLS method employed
RPMI 1640 broth medium, and MICs were read after incubation for 48 h at 35°C. Etest MICs were determined with RPMI agar containing 2%
glucose and with Casitone agar and were read after incubation for
24 h (Aspergillus spp. and Rhizopus spp.) and 48 h (all species except Rhizopus spp.) at 35°C.
The isolates included Aspergillus flavus, Aspergillus
fumigatus, Aspergillus niger, Aspergillus
terreus, Fusarium spp., Pseudallescheria
boydii, Rhizopus spp., Paecilomyces
variotii, and an Acremonium sp. Overall agreement
between Etest and microdilution MICs was 96% with RPMI agar and 80%
with Casitone agar. The agreement was 100% for all species except
Rhizopus spp. (83%) and Paecilomyces varioti
(0%) with RPMI agar. When Casitone agar was used, the agreement ranged from 50% with Rhizopus spp. to 100% with
Fusarium spp., P. boydii, P. varioti, and an Acremonium sp. Notably, for
Aspergillus spp., the agreement between itraconazole Etest
MICs read at 24 h and reference microdilution MICs read at 48 h was 100% with both RPMI and Casitone agar. Both media supported the
growth of all filamentous fungi tested. Where a discrepancy was
observed between Etest and the reference method, the Etest MIC was
generally higher. The Etest method using RPMI agar appears to be a
useful method for determining itraconazole susceptibilities of
Aspergillus spp. and other filamentous fungi.
*
Corresponding author. Mailing address: Medical
Microbiology Division, C606 GH, Department of Pathology, University of
Iowa College of Medicine, Iowa City, IA 52242. Phone: (319) 384-9566. Fax: (319) 356-4916. E-mail: michael-pfaller{at}uiowa.edu.
Journal of Clinical Microbiology, September 2000, p. 3359-3361, Vol. 38, No. 9
0095-1137/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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