Colorimetric Assay for Antifungal Susceptibility Testing of Aspergillus Species

Abstract
A colorimetric assay for antifungal susceptibility testing of Aspergillus species ( Aspergillus fumigatus , Aspergillus flavus , Aspergillus terreus , Aspergillus nidulans , and Aspergillus ustus ) is described based on the reduction of the tetrazolium salt 2,3-bis(2-methoxy-4-nitro-5-[(sulphenylamino)carbonyl]-2H-tetrazolium-hydroxide (XTT) in the presence of menadione as an electron-coupling agent. The combination of 200 μg of XTT/ml with 25 μM menadione resulted in a high production of formazan within 2 h of exposure, allowing the detection of hyphae formed by low inocula of 10 2 CFU/ml after 24 h of incubation. Under these settings, the formazan production correlated linearly with the fungal biomass and less-variable concentration effect curves for amphotericin B and itraconazole were obtained.

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