BACKGROUND

Aspergillus fumigatus is the main cause of invasive aspergillosis and triazole antifungals are the primary treatment option. The effectiveness of triazole therapy is hampered by the emergence of resistance, mainly caused by mutations in the cyp51A gene and a tandem repeat (TR) of 34 bases (TR/Leu98His) and 46 bases (TR/Tyr121Phe/Thr289Ala) in the promoter region, which correspond with signature triazole resistance phenotypes. We aimed to investigate the occurrence of triazole phenotype and genotype variation over a 29-year period in the Netherlands.

METHODS

In this genomic and phenotypic study, we screened all clinical A fumigatus isolates from Dutch hospitals collected between Jan 6, 1994, and Dec 31, 2022, for resistance to triazole using agar-based methods, and characterised them by sequencing the cyp51A gene and in vitro susceptibility testing using the European Committee on Antimicrobial Susceptibility Testing reference method. Whole-genome sequencing was performed on selected isolates, including those harboring TR variants, high-frequency single-nucleotide polymorphisms, and wild-type strains. Clinical information such as age, underlying disease, diagnosis, therapy, and outcomes was collected for patients who had isolates cultured at the Radboud University Medical Centre, Nijmegen, Netherlands, between Jan 1, 2017, and Dec 31, 2022.

FINDINGS

1979 (15·6%) of the screened 12 679 A fumigatus isolates harboured cyp51A triazole resistance mutations, predominately TR/Leu98His sensu stricto in 1338 (67·6%) resistant isolates and TR/Tyr121Phe/Thr289Ala sensu stricto in 332 (16·8%) resistant isolates. Phenotype and genotype variations were observed in 325 (17·2%) triazole resistant isolates harbouring a TR-resistance mechanism, including 12 cyp51A genotype variants. Whole-genome sequencing showed that isolates with combinations of TR-based and TR-based polymorphisms seemed to be derived from separate populations, but there was some overlap. 59 cases of proven or probable invasive aspergillosis were identified, including 13 triazole-resistant cases, of which three were caused by genotype variants. Mixed genotype infection was observed in 11 (84·6%) of 13 triazole-resistant patients and the number of antifungal treatment switches was higher compared with triazole-susceptible disease (p<0·0001).

INTERPRETATION

Our study showed variation in triazole genotypes and phenotypes in clinical A fumigatus isolates with cyp51A-mediated resistance, some of which were cultured from triazole-resistant invasive aspergillosis cases. Triazole resistance variation and mixed A fumigatus genotypes represent a major challenge in clinical management of Aspergillus diseases because current molecular diagnostic tools will increasingly fail to predict the resistance phenotype, underscoring the need for improved detection methods.

FUNDING

National Key Research and Development Program of China, National Natural Science Foundation of China, and Wellcome Trust.