Evaluation of Etest and Disk Diffusion Methods Compared to Broth Microdilution Antifungal Susceptibility Testing of Posaconazole Against Clinical Isolates of Candida.

D. J. DIEKEMA, S. MESSER, R. HOLLIS, L. BOYKEN, S. TENDOLKAR, J. KROEGER, M. A. PFALLER;

Author address: 

Univ. of Iowa Coll. of Med., Iowa City, IA.

Abstract: 

Background: Broth microdilution (BMD) is a reference method for antifungal susceptiblity testing (AFST), but agar-based methods such as Etest and disk diffusion (DD) may be preferred by some clinical laboratories for their simplicity and ease of use. These methods must be validated against BMD for newer antifungal agents such as posaconazole (POS). Methods: We performed Etest (AB Biodisk), DD (5 µg POS disk (Oxoid), Clinical and Laboratory Standards Institute (CLSI) M44-A method) and BMD (CLSI M27-A2 method) AFST of POS against clinical isolates of Candida spp. collected from 60 medical centers during 2004-2005. The isolates included 54% C. albicans, 17% C. parapsilosis, 12% C. glabrata, 11% C. tropicalis, 3% C. krusei, and 3% other Candida spp. DD and Etest results were compared to the gold standard of BMD. For the sake of method comparison only, we applied the MIC and DD breakpoints recently approved for voriconazole: Susceptible (S): =17 mm; Susceptible Dose-Dependent (SDD): 2 µg/ml, 14-16 mm; and Resistant (R): >= 4 µg/ml, =4 µg/ml) by BMD testing. Conclusions: POS AFST results by DD and Etest correlated well with the CLSI M27-A2 BMD method. These agar based methods hold promise as simple and reliable methods for determining POS susceptibility of Candida spp.
2006

abstract No: 

M-1573

Full conference title: 

46th Interscience Conference on Antimicrobial Agents and Chemotherapy
    • ICAAC 46th