Voriconazole activity against clinical yeast isolates: a multicentre Italian study

The activity of voriconazole was tested in vitro against 1996 clinical yeast isolates collected in 20 Italian microbiology laboratories. Voriconazole susceptibility testing was carried out with the broth microdilution (NCCLS M27-A2), Etest and disk diffusion methods. The minimum inhibitory concentrations at which 90% of the isolates were inhibited (MIC90) obtained with the NCCLS method were 0.03 mg/L for Candida albicans, 0.5 mg/L for Candida non-albicans and 0.25 mg/L for other genera; those obtained with Etesting were, respectively, 0.032 mg/L, 0.125 mg/L and 0.125 mg/L. With the disk diffusion method, the majority of isolates (92.3%) showed inhibition zone diameters between 21 mm and 40 mm. Using a tentative MIC cut-off of 1 mg/L as indicative of in vitro susceptibility, 98.1% of the isolates tested in our study would be classified as susceptible, and only 28 (1.4%) of the isolates, with MICs higher than 2 mg/L, would be classified as resistant to the drug. Our findings confirm the broad-spectrum in vitro activity of voriconazole against yeasts, including Candida species that are generally less susceptible to other azoles.