title: Spectrophotometric reading of EUCAST antifungal susceptibility testing of Aspergillus fumigatus.
abstract: OBJECTIVE
  Given the increasing number of antifungal drugs and the emergence of resistant Aspergillus isolates, objective, automated and high-throughput antifungal susceptibility testing is important. The EUCAST E.Def 9.3 reference method for MIC determination of Aspergillus species relies on visual reading. Spectrophotometric reading was not adopted because of concern that non-uniform filamentous growth might lead to unreliable and non-reproducible results. We therefore evaluated spectrophotometric reading for the determination of MICs of antifungal azoles against Aspergillus fumigatus.
  
  
  METHODS
  Eighty-eight clinical isolates of A. fumigatus were tested against four medical azoles (posaconazole, voriconazole, itraconazole, isavuconazole) and one agricultural azole (tebuconazole) with EUCAST E.Def 9.3. The visually determined MICs (complete inhibition of growth) were compared with spectrophotometrically determined MICs and essential (±1 twofold dilution) and categorical (susceptible/intermediate/resistant or wild-type/non-wild-type) agreement was calculated. Spectrophotometric data were analysed with regression analysis using the Emaxmodel, and the effective concentration corresponding to 5% (EC5) was estimated.
  
  
  RESULTS
  Using the 5% cut-off, high essential (92%-97%) and categorical (93%-99%) agreement (<6% errors) was found between spectrophotometric and visual MICs. The EC5also correlated with the visually determined MICs with an essential agreement of 83%-96% and a categorical agreement of 90%-100% (<5% errors).
  
  
  CONCLUSIONS
  Spectrophotometric determination of MICs of antifungal drugs may increase objectivity, and allow automation and high-throughput of EUCAST E.Def 9.3 antifungal susceptibility testing of Aspergillus species.
authors: Clinical Microbiology Laboratory, Attikon University Hospital, National and Kapodistrian University of Athens, Greece; Department of Medical Microbiology and Infectious Diseases, Erasmus Medical Center Rotterdam, Netherlands. Electronic address: jmeletiadis@med.uoa.gr.
authors: J
authors: J
authors: Meletiadis
authors: Unit of Mycology, Department Microbiological Surveillance and Research, Statens Serum Institut, Copenhagen, Denmark; Department of Clinical Microbiology, Copenhagen University, Rigshospitalet, Copenhagen, Denmark.
authors: K
authors: K
authors: Leth Mortensen
authors: Department of Medical Microbiology, Radboud University Medical Center, Nijmegen, The Netherlands; Centre of Expertise in Mycology, Radboudumc/CWZ, Nijmegen, The Netherlands.
authors: P E
authors: PE
authors: Verweij
authors: Department of Medical Microbiology and Infectious Diseases, Erasmus Medical Center Rotterdam, Netherlands.
authors: J W
authors: JW
authors: Mouton
authors: Unit of Mycology, Department Microbiological Surveillance and Research, Statens Serum Institut, Copenhagen, Denmark; Department of Clinical Microbiology, Copenhagen University, Rigshospitalet, Copenhagen, Denmark; Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark.
authors: M C
authors: MC
authors: Arendrup
mesh_terms: D000935:Antifungal Agents / Q000494:pharmacology*; D001228:Aspergillosis / Q000175:diagnosis* / Q000382:microbiology*; D001232:Aspergillus fumigatus / Q000187:drug effects* / Q000302:isolation & purification; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D025141:Drug Resistance, Fungal; D005656:Fungal Proteins / Q000235:genetics; D005838:Genotype; D057166:High-Throughput Screening Assays; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods*; D009154:Mutation; D013053:Spectrophotometry / Q000379:methods*
chemical_list: D000935:Antifungal Agents; D005656:Fungal Proteins; D003577:Cytochrome P-450 Enzyme System; C465526:cytochrome P-450 CYP51A, Aspergillus
keywords: Antifungal susceptibility; Aspergillus; EUCAST; Spectrophotometric; Triazoles