Azole resistance screening in Aspergillus fumigatus sensu stricto using the azole-containing agar method (EUCAST E.Def 10.2): conidial suspension filtration and inoculum adjustment before inoculum preparation may not be needed

• Published in: Journal of clinical microbiology Vol. 62; no. 7; p. e0036924
• Main Authors: Serrano-Lobo, Julia, Reigadas, Elena, Muñoz, Patricia, Escribano, Pilar, Guinea, Jesús
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 16.07.2024
• Subjects: Agar; Antifungal Agents - pharmacology; Antimicrobial Chemotherapy; Aspergillus fumigatus - drug effects; Aspergillus fumigatus - genetics; Aspergillus fumigatus - isolation & purification; Azoles - pharmacology; Culture Media - chemistry; Cytochrome P-450 Enzyme System - genetics; Drug Resistance, Fungal; Fungal Proteins - genetics; Humans; Microbial Sensitivity Tests - methods; Mycology; Spores, Fungal - drug effects; Spores, Fungal - genetics; azole resistance; azole-containing plates; detection; E.Def 10.2; EUCAST; Aspergillus fumigatus
• ISSN: 0095-1137; 1098-660X; 1098-660X
• DOI: 10.1128/jcm.00369-24

Azole resistance screening in can be routinely carried out by using azole-containing agar plates (E.Def 10.2 procedure); however, conidial suspension filtering and inoculum adjustment before inoculum preparation are time-consuming. We evaluated whether skipping the filtration and inoculum adjustment steps negatively influenced the performance of the E.Def 10.2 procedure. isolates ( = 98), previously classified as azole susceptible or azole resistant (E.Def 9.4 method), were studied. Azole-resistant isolates had either the wild-type gene sequence ( = 1) or the following gene substitutions: TR -L98H ( = 41), G54R ( = 5), TR -Y121F-T289A ( = 1), or G448S ( = 1). In-house azole-containing agar plates were prepared according to the EUCAST E.Def 10.2 procedure. Conidial suspensions obtained by adding distilled water (Tween 20 0.1%) were either filtered and the inocula adjusted to 0.5 McFarland or left unfiltered and unadjusted. Agreements between the agar screening methods using inocula prepared by each procedure were high for itraconazole (99%), voriconazole (100%), and posaconazole (94.9%). Sensitivity and specificity (considering the susceptibility category as per the microdilution E.Def 9.4 method as the gold standard) of E.Def 10.2 were 100% to rule in or rule out resistance when unfiltered and unadjusted suspensions were used; the resistance phenotype of isolates harboring the TR -L98H, G54R, or TR -Y121F-T289A substitutions was correctly detected. Unfiltered and unadjusted conidial suspensions do not negatively influence the performance of the E.Def 10.2 method when screening for azole resistance in . Azole resistance screening in can be routinely carried out by using azole-containing plates (E.Def 10.2 procedure); however, conidial suspension filtering and inoculum adjustment before inoculation of plates are time-consuming. We, here, showed that unfiltered and unadjusted conidial suspensions do not negatively influence the performance of the E.Def 10.2 method when screening for azole resistance in .