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Journal of Clinical Microbiology, June 2007, p. 1811-1820, Vol. 45, No. 6
0095-1137/07/$08.00+0 doi:10.1128/JCM.00134-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Virginia Commonwealth University Medical Center, Richmond, Virginia,1 Centers for Disease Control, Atlanta, Georgia,2 Women's and Children's Hospital, North Adelaide, South Australia, Australia,3 University of Iowa, Iowa City, Iowa,4 University of Texas, San Antonio, Texas,5 Giles Scientific Inc., Santa Barbara, California6
Received 18 January 2007/ Returned for modification 9 March 2007/ Accepted 2 April 2007
The purpose of this study was to correlate inhibition zone diameters, in millimeters (agar diffusion disk method), with the broth dilution MICs or minimum effective concentrations (MECs) (CLSI M38-A method) of five antifungal agents to identify optimal testing guidelines for disk mold testing. The following disk diffusion testing parameters were evaluated for 555 isolates of the molds Absidia corymbifera, Aspergillus sp. (five species), Alternaria sp., Bipolaris spicifera, Fusarium sp. (three species), Mucor sp. (two species), Paecilomyces lilacinus, Rhizopus sp. (two species), and Scedosporium sp. (two species): (i) two media (supplemented Mueller-Hinton agar [2% dextrose and 0.5 µg/ml methylene blue] and plain Mueller-Hinton [MH] agar), (ii) three incubation times (16 to 24, 48, and 72 h), and (iii) seven disks (amphotericin B and itraconazole 10-µg disks, voriconazole 1- and 10-µg disks, two sources of caspofungin 5-µg disks [BBL and Oxoid], and posaconazole 5-µg disks). MH agar supported better growth of all of the species tested (24 to 48 h). The reproducibility of zone diameters and their correlation with either MICs or MECs (caspofungin) were superior on MH agar (91 to 100% versus 82 to 100%; R, 0.71 to 0.93 versus 0.53 to 0.96 for four of the five agents). Based on these results, the optimal testing conditions for mold disk diffusion testing were (i) plain MH agar; (ii) incubation times of 16 to 24 h (zygomycetes), 24 h (Aspergillus fumigatus, A. flavus, and A. niger), and 48 h (other species); and (iii) the posaconazole 5-µg disk, voriconazole 1-µg disk, itraconazole 10-µg disk (for all except zygomycetes), BBL caspofungin 5-µg disk, and amphotericin B 10-µg (zygomycetes only).
Published ahead of print on 11 April 2007.
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