Evaluation of disk diffusion method compared to broth microdilution for antifungal susceptibility testing of 3...

We tested the susceptibility of caspofungin, micafungin, and anidulafungin against Aspergillus spp. isolates by the new Clinical and Laboratory Standards Institute M51-A disk diffusion (DD) and the broth microdilution methods. A total of 65 clinical isolates of Aspergillus spp. were evaluated. The DD assay was performed on nonsupplemented Müeller-Hinton agar using caspofungin 2-μg, micafungin 1-μg, and anidulafungin 2-μg disks. Echinocandin minimal effective concentrations (MECs) and inhibition zones (IZs) were read after 24 to 48 (A. terreus) h at 35 °C. Caspofungin MECs for all Aspergillus spp. strains tested were ≤ 0.25 μg/mL; IZs were ≥ 15 mm for most species except for A. terreus (11-22 mm). Both micafungin and anidulafungin MECs were ≤ 0.015 μg/mL, but micafungin IZs were ≥ 14 mm while anidulafungin IZs were ≥ 22 mm. As for caspofungin, the DD method could be a useful method for susceptibility testing of micafungin and anidulafungin against Aspergillus spp.