In vitro azole susceptibility of 201 itraconazole resistant and 176 wildtype Aspergillus fumigatus isolates in relation to proposed CLSI epidemiologic cuttof values

Jacques F. Meis, Ferry Hagen, Ilse Curfs-Breuker, Anuradha Chowdhary, Paul E. Verweij


Objectives: To determine in vitro azole susceptibility of a collection of 201 itraconazole resistant and 176 wild-type (WT) Aspergillus fumigatus isolates. Methods: Azole resistant A. fumigatus isolates (n = 201) with TR34/L98H, TR46/Y121F/T289A, G54 and M220 mutations and WT isolates (n = 178) were included. MICs were determined using the CLSI-M38A2 methodology and interpreted by using proposed CLSI epidemiologic cut-off values (ECVs) to separate WT from non-WT isolates (itraconazole and voriconazole > 1 mg/L, posaconazole > 0.5 mg/L). Origin of isolates was respiratory samples from patients with cystic fibrosis, pulmonary diseases or intubated patients at the ICU. All isolates were typable by STRAf microsatellite typing. Results: All isolates were A. fumigatus and 201/378 strains were resistant to azoles. No cryptic species were identified. Of the resistant isolates, 126 contained the TR34/L98H mutation, 52 contained the TR46/Y121F/T289A mutation and 23 resistant isolates had other or no detectable cyp51A mutations. Posaconazole had the lowest in vitro MIC90 and GM among all, followed by itraconazole and voriconazole. Seven isolates harboured other cyp51A mutations (M220, G54, G432), which have been shown to confer azole resistance. Of the TR34/L98H isolates, 100% (126/126) were itraconazole non-WT (MICs > 1 mg/L), 92.2% (117/126) were voriconazole non-WT (MICs > 1 mg/L) and only 19% (24/126) had a non-WT phenotype of posaconazole (MICs > 0.5 mg/L). All TR46/Y121F/T289A isolates had non-WT voriconazole MICs, 92.3% (58/62) non-WT itraconazole MICs and 25% (13/52) were above the ECV of posaconazole. Conclusions: The TR34/L98H and TR46/Y121F/T289A, M220, G432 and G54 cyp51A genotypes of A. fumigatus show distinct resistance phenotypes. More than 99% of WT isolates had a posaconazole MIC of ≤0.25mg/L. Of the azole resistant isolates with TR34/L98H and TR46/Y121F/T289A mutations only 19% and 25% respectively were non-WT. This raises the question if the proposed CLSI ECV of 0.5mg/L for posaconazole is able to separate WT from non-WT A. fumigatus.


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19th Congress of the International Society for Human and Animal Mycology
    • ISHAM 19th (2015)