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- Title
Use of high inoculum for early metabolic signalling and rapid susceptibility testing of Aspergillus species.
- Authors
Charalampos Antachopoulos; Joseph Meletiadis; Tin Sein; Emmanuel Roilides; Thomas J. Walsh
- Abstract
<sec><st>Objectives</st> To develop and evaluate a new method for rapid susceptibility testing of <it>Aspergillus</it> spp. based on early metabolic signalling of high-inoculum biomass. </sec> <sec><st>Methods</st> Susceptibility to amphotericin B and voriconazole was studied in 39 clinical isolates of <it>Aspergillus</it> spp. (16 <it>Aspergillus fumigatus</it>, 11 <it>Aspergillus flavus</it>, 12 <it>Aspergillus terreus</it>). At 6 or 8 h after inoculation for <it>A. fumigatus</it> and <it>A. flavus</it>, and at 8 or 12 h after inoculation for <it>A. terreus</it>, 100 µg/mL of the tetrazolium salt XTT and 25 µM menadione were added and absorbance measured at 450 nm after 2 h of incubation at 37°C. Inocula used were 106 conidia/mL for <it>A. fumigatus</it> and <it>A. terreus</it> and 105 conidia/mL for <it>A. flavus</it>, as lower inocula exhibited very low metabolic activity at these time points. Data were analysed with the sigmoid <it>E</it><inf>max</inf> model and compared with visual (lowest drug concentration showing no growth) and spectrophotometric MIC determination at 48 h (CLSI M38-A method). </sec> <sec><st>Results</st> The <it>E</it><inf>max</inf> model described well the concentration–effect relationship for early metabolic activity and 48 h fungal biomass (median <it>r</it>2: 0.97 and 0.93, respectively). Use of the model allowed characterization and quantification of species- and drug-related differences in pharmacological inhibition of early metabolic activity as well as calculation of appropriate cutoff levels for MIC determination with the XTT assay. Using these cutoff levels, for <it>A. fumigatus</it> and <it>A. flavus</it> at both time points (6 and 8 h) and for <it>A. terreus</it> at 12 h, the agreement (± one dilution) of the XTT assay with the CLSI method was 91–100% and its reproducibility was 97–100%. </sec> <sec><st>Conclusions</st> This newly developed high-inoculum-based method provides rapid and reproducible MIC determinations for <it>Aspergillus</it> spp. </sec>
- Subjects
MONILIACEAE; ASPERGILLUS; BIOMASS; POLYENE antibiotics
- Publication
Journal of Antimicrobial Chemotherapy (JAC), 2007, Vol 59, Issue 2, p230
- ISSN
0305-7453
- Publication type
Article