Azole and amphotericin B minimum inhibitory concentrations against Aspergillus fumigatus: high agreement between spectrophotometric and visual readings using the EUCAST 9.3.2 procedure.

The EUCAST 9.3.2 procedure recommends visual readings of azole and amphotericin B MICs against Aspergillus spp. Visual determination of MICs may be challenging. In this work, we aim to obtain and compare visual and spectrophotometric MICs readings of azoles and amphotericin B against A. fumigatus sensu lato isolates.Eight hundred and forty-seven A. fumigatus sensu lato isolates (A. fumigatus sensu stricto [n=828] and cryptic species [n=19]) were tested against amphotericin B, itraconazole, voriconazole, posaconazole, and isavuconazole using the EUCAST EDef 9.3.2 procedure. Isolates were classified as susceptible or resistant/non-wild-type according to the 2020 updated breakpoints. The area of technical uncertainty for the azoles was defined in the updated breakpoints. Visual and spectrophotometric (fungal growth reduction >95% compared to control; read at 540 nm) MICs were compared. Essential (±1 twofold dilutions) and categorical agreements were calculated.Overall, high essential (97.1%) and categorical (99.6%) agreements were found. We obtained 100% categorical agreements for amphotericin B, itraconazole, and posaconazole and, consequently, no errors were found. Categorical agreements were 98.7% and 99.3% for voriconazole and isavuconazole, respectively. Most of misclassifications for voriconazole and isavuconazole were found to be associated with MIC results falling either in the area of technical uncertainty or in one two-fold dilutions above the breakpoint. Resistance rate was slightly lower when the MICs were obtained by spectrophotometric readings. However, all relevant cyp51A mutants were correctly classified as resistant.Spectrophotometric determination of azole and amphotericin B MICs against A. fumigatus sensu lato isolates may be a convenient alternative to visual endpoint readings.