The evaluation of in vitro pharmacodynamic properties of amphotericin B, voriconazole and caspofungin against A. fumigatus isolates by the conventional and colorimetric time-kill assays.

Aspergillus fumigatus is an opportunistic pathogen responsible for life-threatening infections in immuncompromised patients. Data about the in vitro pharmacodynamics of antifungals against A. fumigatus are limited. In the present study, we investigated the fungicidal activities, at concentrations of 1, 4 and 16 times the minimum inhibitory concentration (MIC), of caspofungin (CAS), amphotericin B (AMB) and voriconazole (VORI) against eight A. fumigatus isolates through the use of time kill and 2,3-Bis [2-methoxy-4-nitro-5-(sulfenylamino) carbonyl-2H-tetrazolium-hydroxide] (XTT) reduction tests. By the conventional time kill test, AMB was fungicidal (≥99.9% reduction in colony forming units; CFU) for all isolates at 4-16 MICs after 48 h incubation. The fungicidal effect for VORI was determined at 4 × MIC for one isolate and at 16 × MIC for four isolates at 48 h of exposure. CAS was also fungicidal at 1 × MIC for one isolate and at 4-16 MICs for two isolates at 48 h. While the percentage of median killing of AMB was found by the time-kill method with XTT as 99% at 4 × MIC and 99.28% at 16 × MIC, that of VORI was 94.5% at 4 × MIC and 92.88% at 16 × MIC after 48 h of incubation. However, a significant increase was observed compared to initial inoculum size with CAS after 48 h. Since the XTT method measures all cellular viability in media, it may give more reliable results about pharmacodynamics of antifungal agents against Aspergillus spp. than the time kill test.