Comparison of the Sensititre YeastOne colorimetric antifungal panel and Etest with the NCCLS M38-A method to determine the activity of amphotericin B and itraconazole against clinical isolates of Aspergillus spp.

Objective: The evaluation of the Sensititre YeastOne and Etest methods for determining susceptibility to amphotericin B and itraconazole by comparing the MICs obtained by these methods at different times of reading with those of the M38-A broth microdilution method. Methods: Sixty-three clinical isolates of Aspergillus spp. (23 Aspergillus flavus, 24 Aspergillus fumigatus, nine Aspergillus niger, three Aspergillus glaucus, two Aspergillus terreus and two Aspergillus flavipes) were assayed. Two itraconazole-resistant strains (NCPF7100 and 7099) were also included. Results: Itraconazole MICs for the two resistant strains were >4 mg/L by the three methods. The overall agreement (+/-2 log(2)) between M38-A (48 h) and colorimetric (48 h) method was 93.4% for amphotericin B and 90.2% for itraconazole. By the Etest, the best agreement with M38-A was obtained when readings were made at 24 h: 88.5% for amphotericin B and 67.2% for itraconazole. Etest MICs were higher for all species except A. niger. Conclusions: The colorimetric method appears to be a suitable alternative procedure for antifungal susceptibility testing of Aspergillus spp. and is able to detect resistance to itraconazole. The range of MICs for amphotericin B by Etest is wider and for some strains is >16 mg/L, suggesting that this method could be useful for detecting resistant strains as occur in yeasts.