Evaluation of the Etest method for susceptibility testing of Aspergillus spp. and Fusarium spp. to three echinocandins

Abstract

We performed Etest and broth microdilution (BMD) susceptibility testing of caspofungin, micafungin and anidulafungin against 67 clinical isolates of Aspergillus spp. and 10 Fusarium spp. Minimal effective concentrations (MECs) by BMD were read after 24 h of incubation at 35°C and Etest MICs were read at 24 and 48 h. MECs ≤0.25 mg/l were obtained with caspofungin for all Aspergillus spp. tested but Etest MICs were ≤1 mg/l at 24 h. The agreement between caspofungin Etest and broth microdilution was good for all Aspergillus species tested (range 82.4100%) except for A. niger and A. glaucus at 24 h of incubation. Micafungin and anidulafungin MEC and MIC results were lower than those of caspofungin (≤0.015 mg/l) at 24 and 48 h for all Aspergillus tested. The agreement between the methods was excellent (100%) for micafungin and anidulafungin for all Aspergillus species tested. The three echinocandins were inactive against all isolates of Fusarium spp. showing MECs and MICs >8 mg/l. The Etest method could be a suitable procedure to test the susceptibility of most Aspergillus species to caspofungin, micafungin and anidulafungin; the best agreement was at 24 h. © 2010 ISHAM.