Background: Micafungin (MCFG) is a new antifungal agent with excellent in vivo anti-Aspergillus fumigatus activity. However, MCFG does not show fungicidal activity against A. fumigatus in vitro, but does strongly inhibit hyphal elongation. In order to characterize the relationship between MCFG concentrations and effect against A. fumigatus, we have performed quantitative analysis with a viability-specific fluorescent dye. Methods: Hyphae of A. fumigatus TIMM0063 were stained with 5(6)-carboxyfluorescein diacetate (CFDA) after exposure to MCFG, and were observed microscopically, and the time course for relative fluorescent units (RFU) was determined. RFU for 5 clinical isolates were determined after 15 h exposure to MCFG, and graphs of RFU (% of control) versus MCFG concentration (multiple of the MIC) were plotted. Data was analyzed by fitting to a sigmoid maximum effect (Emax) model. Results: Drug-free control hyphae were well extended and stained with CFDA. In contrast, flattened hyphal cells, resulting from exposure to MCFG, were only slightly stained with CFDA, which indicated that MCFG induced cell killing. In the time course study, control cells stained with CFDA showed an increase in RFU up to 24 h. In contrast, hyphae exposed to MCFG showed a concentration-independent inhibition of increase in RFU at concentrations over 1/2 x MIC. Each strain exhibited a sigmoidal concentration-effect profile (R2=0.85-0.98), and the Emax ranged from 31% to 81% inhibition. For A. fumigatus, EC90, the concentration producing 90% of the Emax, was estimated to be 0.80 x MIC. Conclusion: We quantitatively determined the in vitro anti-Aspergillus activity of MCFG using a fluorescent dye-staining method for viable cell detection to indicate inhibition of hyphal elongation and hyphal cell killing. MCFG showed a sigmoidal concentration-effect profile, and is predicted to produce the maximum effect at a concentration of 0.80 x MIC.
Full conference title:
42nd Interscience Conference on Antimicrobial Agents and Chemotherapy
- ICAAC 42nd