Antifungal Susceptibility of the Aspergillus viridinutans Complex: Comparison of Two In Vitro Methods
Abstract
Cryptic species of Aspergillus fumigatus, including the Aspergillus viridinutans species complex, are increasingly reported to be causes of invasive aspergillosis. Their identification is clinically relevant, as these species frequently have intrinsic resistance to common antifungals.
We evaluated the susceptibilities of 90 environmental and clinical isolates from the A. viridinutans species complex, identified by DNA sequencing of the calmodulin gene, to seven antifungals (voriconazole, posaconazole, itraconazole, amphotericin B, anidulafungin, micafungin, and caspofungin) using the reference European Committee on Antimicrobial Susceptibility Testing (EUCAST) method. The majority of species demonstrated elevated MICs of voriconazole (geometric mean [GM] MIC, 4.46 mg/liter) and itraconazole (GM MIC, 9.85 mg/liter) and had variable susceptibility to amphotericin B (GM MIC, 2.5 mg/liter).
Overall, the MICs of posaconazole and the minimum effective concentrations of echinocandins were low. The results obtained by the EUCAST method were compared with the results obtained with Sensititre YeastOne (YO) panels.
Overall, there was 67% agreement (95% confidence interval [CI], 62 to 72%) between the results obtained by the EUCAST method and those obtained with YO panels when the results were read at 48 h and 82% agreement (95% CI, 78 to 86%) when the results were read at 72 h. There was a significant difference in agreement between antifungals; agreement was high for amphotericin B, voriconazole, and posaconazole (70 to 86% at 48 h and 88 to 93% at 72 h) but was very low for itraconazole (37% at 48 h and 57% at 72 h).
The agreement was also variable between species, with the maximum agreement being observed for A. felis isolates (85 and 93% at 48 and 72 h, respectively). Elevated MICs of voriconazole and itraconazole were cross-correlated, but there was no correlation between the other azoles tested.