The population structure of Aspergillus fumigatus clinical isolates: Role of azole drugs in selecting less-susceptible clonal complexes

In the last 10 years, an increase of invasive aspergillosis (IA) due to azole resistant Aspergillus fumigatus isolates has been reported. Recently, an emergent clonal complex (CC) with an azole resistant phenotype has been described in Holland. Here, we genotyped a collection of 114 clinical isolates from 89 patients treated for hematological malignancies, and looked for associations with azole MICs, cytochrome P450 (cyp51a) gene sequence polymorphisms.
Microsatellite markers were used to determine isolate genotypes; analyses were carried out using minimum spanning tree (CC defined by only 1/4 allelic mismatch), whilst MIC to azole ratios were determined by Etest, and their cyp51a gene and its promoter entirely sequenced.

30/114 (26%) isolates were obtained under voriconazole therapy. 69 genotypes clustered in 11 groups (2 to 47 isolates) and 27 genotypes (28 isolates: 24.5%) were unrelated to other genotypes (singletons). One singleton had itraconazole (ITZ) MIC = 16mg/L, and was obtained from a patient without IA (1). Three major clonal complexes (greater than 5 isolates) were individualized: CC1 (n = 47); CC2 (n = 10); CC3 (n = 6). 16 isolates (SNPs isolates) harbored polymorphisms in the promoter, introns and exons (F46Y, M172V, and/or N248T, D255E, E427K) of cyp51a. SNPs isolates harbored decreased susceptibility to ITZ (p = 0.04) but kept MICs less than 2 mg/L. SNPs isolates were associated with CC2 (p less than 0.0001) and with voriconazole pre-exposure in patients (p = 0.003). CC1 was associated with patients for who IA was excluded (p = 0.02).
Voriconazole pre-exposure in hematological patients influences the repartition of A. fumigatus isolates with selection and emergence of isolates harboring SNPs in cyp51a gene, higher ITZ MIC, and belonging to a specific clonal complex.

No relevant conflicts of interest declared.