BACKGROUND: Reference antifungal susceptibility testing of echinocandins against Aspergillus spp. relies on the determination of the minimal effective concentration, which is difficult to perform, time-consuming and subjective. We developed and evaluated in a multicentre study an agar-based screening method for echinocandin susceptibility testing of Aspergillus spp. METHODS: Forty WT isolates [10 Aspergillus fumigatus species complex (SC), 10 Aspergillus flavus SC, 10 Aspergillus terreus SC and 10 Aspergillus niger SC] and 4 non-WT A. fumigatus isolates with or without known fks alterations were used. The optimal test conditions and stability over time were evaluated in preliminary studies monitoring colony growth. Twenty-microlitre aliquots of 1-2 McFarland inocula in 0.1% Tween 20 aqueous solution were added to each well and plates were incubated for 24/48 h at 35 ± 2°C. Subsequently, all isolates were tested blindly at three centres using four-well screening plates, containing anidulafungin, caspofungin, micafungin or no antifungal in each of the four wells, respectively. RESULTS: WT isolates produced fluffy colonies on drug-free agar wells only. The non-WT isolates produced fluffy colonies on echinocandin-containing and control agar wells. Using the echinocandin concentrations of 0.25 mg/L anidulafungin, 1 mg/L caspofungin and 0.125 mg/L micafungin, and the compact (non-fluffy) versus fluffy colony morphology endpoint, all centres successfully discriminated non-WT and WT strains even after 24 h. Among the three echinocandins, anidulafungin produced the clearest endpoints. CONCLUSIONS: The four-well plate agar method is suitable for echinocandin susceptibility screening of Aspergillus spp. and can be used to detect echinocandin non-WT isolates.

Additional Metadata
Persistent URL dx.doi.org/10.1093/jac/dkz154, hdl.handle.net/1765/118593
Journal Journal of Antimicrobial Chemotherapy
Citation
Meletiadis, J, Siopi, M, Kanioura, L, Jørgensen, K.M. (Karin Meinike), Perlin, D.S. (David S.), Mouton, J.W, & Arendrup, M.C. (2019). Development and multicentre validation of an agar-based screening method for echinocandin susceptibility testing of Aspergillus species. Journal of Antimicrobial Chemotherapy, 74(8), 2247–2254. doi:10.1093/jac/dkz154