Synergy, pharmacodynamics, and time-sequenced ultrastructural changes of the interaction between nikkomycin Z and the echinocandin FK463 against Aspergillus fumigatus.
We investigated the potential synergy between two cell wall-active agents, the echinocandin FK463 (FK) and the chitin synthase inhibitor nikkomycin Z (NZ), against 16 isolates of filamentous fungi. Susceptibility testing was performed with a broth macrodilution procedure by NCCLS methods. The median minimal effective concentration (MEC) of FK against all Aspergillus species was 0.25 microg/ml (range, 0.05 to 0.5 microg/ml). For Fusarium solani and Rhizopus oryzae, MECs of FK were >512 microg/ml. The median MEC of NZ against Aspergillus fumigatus was 32 microg/ml (range, 8 to 64 microg/ml), and that against R. oryzae was 0.5 microg/ml (range, 0.06 to 2 microg/ml); however, for the other Aspergillus species, as well as F. solani, MECs were >512 microg/ml. A checkerboard inhibitory assay demonstrated synergy against A. fumigatus (median fractional inhibitory concentration index = 0.312 [range, 0.15 to 0.475]). The effect was additive to indifferent against R. oryzae and indifferent against other Aspergillus spp. and F. solani. We further investigated the pharmacodynamics of hyphal damage by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay and examined the time-sequenced changes in hyphal ultrastructure. Significant synergistic hyphal damage was demonstrated with the combination of NZ (2 to 32 microg/ml) and FK (0.03 to 0.5 microg/ml) over a wide range of concentrations (P < 0.001). The synergistic effect was most pronounced after 12 h of incubation and was sustained through 24 h. Time-sequenced light and electron microscopic studies demonstrated that structural alterations of hyphae were profound, with marked transformation of hyphae to blastospore-like structures, in the presence of FK plus NZ, while fungi treated with a single drug showed partial recovery at 24 h. The methods used in this study may be applicable to elucidating the activity and interaction of other cell wall-active agents. In summary, these two cell wall-targeted antifungal agents, FK and NZ, showed marked time-dependent in vitro synergistic activity against A. fumigatus.
Chiou
C C
CC
Immunocompromised Host Section, Pediatric Oncology Branch, National Cancer Institute, Bethesda, Maryland 20892, USA.
Mavrogiorgos
N
N
Tillem
E
E
Hector
R
R
Walsh
T J
TJ
D000617:Aminoglycosides; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000935:Antifungal Agents / Q000494:pharmacology*; D001232:Aspergillus fumigatus / Q000187:drug effects* / Q000648:ultrastructure; D004357:Drug Synergism; D054714:Echinocandins; D007700:Kinetics; D055666:Lipopeptides; D008074:Lipoproteins / Q000494:pharmacology*; D000077551:Micafungin; D008826:Microbial Sensitivity Tests; D008854:Microscopy, Electron; D010456:Peptides, Cyclic / Q000494:pharmacology*; D013778:Tetrazolium Salts; D013844:Thiazoles
D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D000935:Antifungal Agents; D054714:Echinocandins; D055666:Lipopeptides; D008074:Lipoproteins; D010456:Peptides, Cyclic; D013778:Tetrazolium Salts; D013844:Thiazoles; C011952:nikkomycin; C022616:thiazolyl blue; D000077551:Micafungin