title: Differential fungicidal activities of amphotericin B and voriconazole against Aspergillus species determined by microbroth methodology.
abstract: Antifungal agents may differ in their fungicidal activities against Aspergillus spp. In order to compare the fungicidal activities of voriconazole and amphotericin B against 40 isolates of Aspergillus fumigatus, A. flavus, and A. terreus, we developed a new microbroth colorimetric method for assessing fungicidal activities and determining minimal fungicidal concentrations (MFCs). This methodology follows the antifungal susceptibility testing reference method M-38A for MIC determination. After drug removal and addition of fresh medium, growth of viable conidia adhering to the bottoms of the microtitration wells was assessed by a colorimetric assay of metabolic activity after 24 h of incubation. The new method was faster (six times), reproducible (92 to 97%), and in agreement with culture-based MFCs (91 to 100%). Differential fungicidal activities of voriconazole and amphotericin B were found among the three Aspergillus species, with A. fumigatus and A. flavus having the lowest (1 and 2 mg/liter, respectively) and A. terreus the highest (>16 mg/liter) median amphotericin B MFCs; A. flavus had a lower median voriconazole MFC (4 mg/liter) than the other species (>8 mg/liter; P < 0.05). Amphotericin B was fungicidal (MFC/MIC </= 4) against all A. fumigatus and A. flavus isolates but no A. terreus isolates, whereas voriconazole was fungicidal against 82% of A. flavus isolates and fungistatic (MFC/MIC > 4) against 94% of A. fumigatus and 84% of A. terreus isolates. The new methodology revealed a concentration-dependent sigmoid pattern of fungicidal effects, indicating that fungicidal activity is not an all-or-nothing phenomenon and that some degree of fungicidal action can be found even for agents considered fungistatic based on the MFC/MIC ratio.
authors.affiliation: Pediatric Oncology Branch, National Cancer Institute, Bethesda, MD 20892, USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Meletiadis
authors.forename: Charalampos
authors.initials: C
authors.lastname: Antachopoulos
authors.forename: Theodouli
authors.initials: T
authors.lastname: Stergiopoulou
authors.forename: Spyros
authors.initials: S
authors.lastname: Pournaras
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Roilides
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Walsh
mesh_terms: D000666:Amphotericin B / Q000494:pharmacology*; D000935:Antifungal Agents / Q000494:pharmacology*; D001230:Aspergillus / Q000187:drug effects* / Q000254:growth & development; D015169:Colony Count, Microbial; D003124:Colorimetry; D003470:Culture Media; D008826:Microbial Sensitivity Tests / Q000379:methods*; D011743:Pyrimidines / Q000494:pharmacology*; D011786:Quality Control; D012044:Regression Analysis; D015203:Reproducibility of Results; D013045:Species Specificity; D013172:Spores, Fungal / Q000187:drug effects; D013778:Tetrazolium Salts; D014230:Triazoles / Q000494:pharmacology*; D024483:Vitamin K 3 / Q000494:pharmacology; D065819:Voriconazole
chemical_list: D000935:Antifungal Agents; D003470:Culture Media; D011743:Pyrimidines; D013778:Tetrazolium Salts; D014230:Triazoles; C059087:2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-((phenylamino)carbonyl)-2H-tetrazolium hydroxide; D024483:Vitamin K 3; D000666:Amphotericin B; D065819:Voriconazole