Evaluation of Disk Diffusion (DD) and Etest Compared to Broth Microdilution (BMD) Antifungal Susceptibility Testing (AFST) of Posaconazole (POS) against Clinical Isolates of Filamentous Fungi.

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

Author address: 

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

Abstract: 

Background: The Clinical Laboratory Standards Institute (CLSI) M38-A is the reference method for testing azoles against filamentous fungi, but agar-based methods may provide simple and reliable alternatives. Validation of these methods against the CLSI M38-A method is needed before they are adopted for testing newer antifungal agents such as POS. Methods: We performed in-parallel testing of DD (5 μg POS disk (Becton Dickinson), CLSI M44-A method), Etest (AB Biodisk) and BMD (CLSI M38-A method) AFST of POS against 146 clinical isolates of filamentous fungi collected from 2000-2005. The isolates included 68 Aspergillus fumigatus, 45 A. flavus, 15 A. niger, 9 A. terreus, 3 A. niveus, 2 A. nidulans, 2 Mucor spp. and 4 Rhizopus spp. POS activity was determined by DD using Mueller Hinton with 2% glucose and methylene blue (0.5 μg/ml), by Etest using RPMI agar buffered with MOPS and 2% glucose, and then compared to its activity by the BMD method. For comparison purposes only, the POS breakpoints used were the same as those recently approved for voriconazole; BMD and Etest, Susceptible (S): = 4 μg/ml; and for DD, S: >= 17 mm; SDD: 14-16 mm; R: = 4 μg/ml) by the BMD method. Conclusions: DD and Etest agar-based methods for testing POS correlated well with the M38-A method. These methods represent reliable alternatives for AFST of POS against the filamentous fungi.
2006

abstract No: 

M-1574

Full conference title: 

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