In vitro testing of Aspergillus fumigatus clinical isolates for susceptibility to voriconazole, amphotericin B and itraconazole: comparison of sensititre versus NCCLS M38-A using two different inocula.

Voriconazole, amphotericin B and itraconazole were tested in vitro against 18 strains of Aspergillus fumigatus isolated from cystic fibrosis patients. Susceptibility was tested with the broth microdilution method (M38-A protocol-NCCLS). Results of this reference method were compared with those of an experimental commercial microdilution broth method (Sensititre). Two different inocula, prepared from 2- and 7-day cultures, were used. Minimum inhibitory concentrations (MICs) of the reference method ranged from 0.25 to 2 microg/ml for voriconazole, 0.06 to 1 microg/ml for amphotericin B, 0.016 to >16 microg/ml for itraconazole. There were no significant differences in the MIC ranges or MIC90 values obtained with the two testing methods or with the two types of inocula. These findings confirm the good in vitro activity of voriconazole, itraconazole and amphotericin B against A. fumigatus. They also indicate that reliable susceptibility data can be generated more rapidly by commercial systems and use of 2-day cultures for inoculum preparation.