SRA

Aspergillus fumigatus is the main cause of invasive aspergillosis and triazole antifungals represent primary treatment options. However, the effectiveness of triazole therapy is hampered by the emergence of resistance, mainly caused by TR34/L98H and TR46/Y121F/T289A mutations in the Cyp51A-gene, which correspond with signature triazole resistance phenotypes. Variants, including additional short nucleotide polymorphisms or tandem repeat variations, have been reported, which might alter the triazole phenotype. We investigated the occurrence of triazole phenotype and genotype variation over a 29-year period in the Netherlands. Methods The Radboud University Medical Center Fungal Culture Collection contains 12,679 clinical A. fumigatus isolates from Dutch hospitals collected since 1994. Triazole agar-based screening was used to detect resistant isolates, which were characterized by sequencing of the Cyp51A-gene, in vitro susceptibility testing using the EUCAST microdilution reference method, and genome sequencing. Results In total, 1,982 (15.6%) A. fumigatus isolates harboured triazole-resistance mutations in the cyp51A-gene, predominately TR34/L98H sensu stricto (ss) in 67.7% and TR46/Y121F/T289A ss in 16.8% of resistant isolates. Overall, 33 (1.7%) cyp51A variants were identified, including 7 TR34-variants and 7 TR46-variants. Four TR34-variants and three TR46-variants showed a phenotype change compared to that of TR34/L98H ss and TR46/Y121F/T289A ss respectively. Whole genome sequencing of 182 azole-susceptible and -resistant (cyp51A variants over years) A. fumigatus isolates revealed no temporal distinction, yet TR34 and TR46 isolates are drawn from different backgrounds. Conclusions Our study showed A. fumigatus resistance variant frequency increasing in recent years, some of which correspond with major shifts in phenotype. Emerging resistance variants represent a major challenge in triazole resistance management as our current molecular diagnostic tools will increasingly fail to predict the resistance phenotype. Improved detection methods for resistance variants are needed as well as international resistance surveillance. Furthermore, our study underscores the urgent need to implement effective measures that prevent triazole resistance selection in the environment.