A comparative study of the post-antifungal effect (PAFE) of amphotericin B, triazoles and echinocandins on Aspergillus fumigatus and Candida albicans

Objectives: To study the post-antifungal effect (PAFE) of antifungal drugs on Aspergillus fumigatus by a radiometric assay and compare the results with those obtained for Candida albicans. Methods: A. fumigatus cultures pregrown for 48 h in 96-well microtitre plate were exposed to various concentrations of the antifungal drug for 2 h. The drug-treated mycelia were washed, incubated in RPMI 1640 containing ¹⁴C-labelled amino acids and the accumulation of radioactivity in the mycelia at different time intervals was determined. The PAFE was determined by plotting the amount of radioactivity associated with the mycelia against post-treatment incubation time. The PAFE of antifungal drug on C. albicans was examined by determining the multiplication (cfu/mL) of drug-pretreated cells at different time intervals for 24 h in drug-free medium. Results: Amphotericin B produced a prolonged PAFE (7.5 ± 0.70 h) against A. fumigatus whereas itraconazole (0.5 ± 0.0 h), voriconazole (0.5 ± 0.0 h), posaconazole (0.75 ± 0.35 h), ravuconazole (0.38 ± 0.17 h) and the echinocandins caspofungin (≤0.5 h) and micafungin (≤0.5 h) produced short PAFE. Short exposure (1 h) of C. albicans to low concentrations (0.125-1 mg/L) of amphotericin B (5.3 ± 1.15 h), caspofungin (5.6 ± 0.57 h) and micafungin (5 ± 1.0 h) produced prolonged PAFE whereas the triazoles produced a short (≤0.5 h) PAFE. Conclusions: Determination of ¹⁴C-labelled amino acid accumulation in antifungal drug-pretreated mycelia is a suitable method for studying PAFE in A. fumigatus. Antifungal drugs with fungicidal activity tend to possess longer PAFE compared to fungistatic drugs.