Post-antifungal effect of amphotericin B and voriconazole against germinated Aspergillus fumigatus conidia.

OBJECTIVES

The post-antifungal effect (PAFE) of amphotericin B and voriconazole on germinated Aspergillus fumigatus conidia was studied using the BacT/Alert detection system based on fungal CO(2) production.

METHODS

Germinated conidia of A. fumigatus were exposed to 1-10x MIC of amphotericin B for 1 and 4 h and to 2.5-40x MIC of voriconazole for 4 and 24 h. After removal of the drug by washing, similar numbers of exposed and control germlings were inoculated into Pedi-BacT culture bottles. CO(2) production was automatically monitored until the bottles signalled positive. The difference in time for positive signals in drug-exposed and control bottles was used to calculate the PAFE.

RESULTS

The killing rate of amphotericin B against germlings was both concentration- and time-dependent, as has been previously found for actively growing hyphae. Similarly, voriconazole showed fungicidal effect after 24 h of exposure, but not after 4 h. Amphotericin B induced a long concentration- and time-dependent PAFE, whereas voriconazole resulted in a short and dose-independent PAFE that was significantly longer after 24 h than after 4 h of exposure.

CONCLUSIONS

An automated method is presented for the determination of PAFE on filamentous fungi using quantifiable numbers of germinated conidia. In contrast to previous results obtained from conidia, this method could demonstrate a PAFE of amphotericin B on Aspergillus that shared characteristics similar to that on Candida spp.