Background: The increasing number of patients susceptible to fungal infections together with the fact that Aspergillus spp. has been reported to be resistant to itraconazole both in vivo and in vitro has made it necessary to perform susceptibility tests mainly in those infections refractory to treatment. The reference method M38-P is labour intensive and not available commercially. Method: The in vitro activity of amphotericin B and itraconazole has been assayed against 68 clinical isolates of Aspergillus (30 A. glaucus, 25 A. fumigatus, 9 A. niger, 2 A. terreus, and 2 A. flavus) by the reference M38-P and the Sensititre YeastOne colorimetric methods. Inoculum suspensions were prepared recovering the conidia from a 7-day culture growth on Potato dextrose agar at 35 Â°C, and adjusted to 0.09-0.11 optical density. Final inoculum: 0.5-5 x 104 CFU/mL. MIC readings were performed at 48 h and 72 h. Results: MICs for amphotericin B increased one dilution for 50% and 61% of strains when read at 72 h by the reference and colorimetric method, respectively. While for itraconazole readings did not change for 94% and 58% of the strains, respectively. By the M38-P, all strains were inhibited with ≤1 mg/L of amphotericin B and ≤0.25 mg/L of itraconazole. MIC ranges at 48 h/72 h for colorimetric method were 0.25-2/0.25-4 mg/L for AMB and 0.016-0.25/0.03-0.5 mg/L for itraconazole. The overall agreement (Â± 2 log) between reference and colorimetric method was 95.31% for amphotericin B and 85.7% for itraconazole.
Full conference title:
11th European Congress of Clinical Microbiology and Infectious Diseases
- ECCMID 11th (2001)