Azole and Amphotericin B MIC Values against Aspergillus fumigatus : High Agreement between Spectrophotometric and Visual Readings Using the EUCAST EDef 9.3.2 Procedure

Abstract

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.

Calcimycin Inhibits Cryptococcus neoformans In Vitro and In Vivo by Targeting the Prp8 Intein Splicing

“…However, all five clinical isolates of Afu were resistant to CMN but susceptible to known antifungals 5-FC (MIC = 3–12 μg/mL) and AmB (MIC = 180 ng/mL). The MICs for Afu were in line with the published MICs of 6 μg/mL for 5-FC and 0.2–1 μg/mL for AmB . Many fungal pathogens belong to Candida spp.…”

“…The MICs for Af u were in line with the published MICs of 6 μg/mL for 5-FC 94 and 0.2−1 μg/mL for AmB. 95 Many fungal pathogens belong to Candida spp. and are major sources of hospital-acquired infections.…”

In Vitro Susceptibilities of Worldwide Isolates of Intrapulmonary Aspergillus Species and Important Candida Species in Sterile Body Sites against Important Antifungals: Data from the Antimicrobial Testing Leadership and Surveillance Program, 2017–2020

“…An analysis of POS concentration monitoring in IPA treatment showed a strong clinical concentration-efficacy relationship ( 36 ). In this survey, the susceptibility rate of POS to intrapulmonary A. fumigatus isolates (18.9%; Table 1 ) was significantly different from that in a Spanish investigation (94 to 94.5%; P < 0.001) ( 20 ). However, the PK characteristics of POS ( Table 5 ) include the following: the protein affinity was 98%, the half-life was 24 to 27 h ( 37 ), the mean plasma C max was 3.2 μg/mL following administration of multiple doses of 400 mg twice daily ( 38 ), the ratio of penetration from plasma to ELF ranged from 0.20 to 0.31 in terms of total concentrations ( 39 ), and the mean value of the area under the concentration-time curve (AUC) from 0 to 12 h (AUC 0–12 ) in ELF ranged from 11.2 to 18.3 mg · h/L following oral administration of multiple doses of 400 mg twice daily in humans ( 40 , 41 ).…”

“…In contrast, a high in vitro NS rate of AMB against clinical A. fumigatus isolates (80.2% of which exhibited MICs of ≥4 μg/mL) was found in Hamilton, Canada in 2015 ( 19 ). The present antifungal study also revealed significantly lower in vitro susceptibility rates of AMB against 660 pulmonary A. fumigatus isolates (49.5%; Table 1 ) and 22 VRC-resistant A. fumigatus isolates (45.5%; Table 1 ) compared to a 2019 Spanish study (98.5% against 847 clinical A. fumigatus sensu lato isolates; P < 0.001) ( 20 ) and a 2010 to 2016 Portugal study (84.7% against 190 clinical A. fumigatus isolates; P < 0.001) ( 21 ). There is a significant diversity in the susceptibilities of AMB to A. fumigatus isolates collected from different countries.…”

Updated EUCAST Clinical Breakpoints against Aspergillus, Implications for the Clinical Microbiology Laboratory

“…However, visual inspection may be challenging and the presence of tiny colonies may raise doubts about MIC interpretation. A recent study compared azole and amphotericin B MICs against A. fumigatus complex isolates obtained visually and spectrophotometrically (to overcome subjectivity) [32], showing high agreement between both methods, including for A. fumigatus sensu stricto isolates harbouring the dominant cyp51A gene mutation. The authors concluded that spectrophotometric MIC reading is a useful alternative to visual inspection and may become an option for determining MIC endpoints of azoles and amphotericin B in the near future.…”