No Evidence for Environmental Triazole Resistance Selection Route in Aspergillus Section Flavi, The Netherlands, 1994-2023.

Aspergillus section Flavi comprises opportunistic pathogens such as Aspergillus flavus, posing significant health risks. Unlike A. fumigatus, where environmental selection drives widespread resistance, it is uncertain whether A. flavus develops azole resistance through a similar environmental route. This study analyzed 544 Aspergillus section Flavi isolates collected from 534 patients in Dutch hospitals (1994-2023). Calmodulin sequencing was used for molecular identification. Antifungal susceptibility testing (AFST) was performed according to EUCAST (European Committee on Antimicrobial Susceptibility Testing) guidelines. Cyp51A was sequenced and mutations were mapped onto the CYP 51 protein 3D model for azole-resistant or non-wild-type isolates. Clinical data, including azole exposure history and underlying diseases, were correlated with the resistance profiles. Of the 544 isolates, 520 were identified as A. flavus and 24 as related species, including A. tamarii (16), A. parasiticus (3), A. nomiae (2), A. pseudonomiae (2), and A. pseudocaelatus (1). Fourteen isolates from five patients were azole-resistant/non-WT, with resistance rates ranging from 0.2 to 0.8%. Resistant/non-WT isolates were associated with chronic diseases and prior clinical azole exposure. Among 10 patients with proven/probable invasive aspergillosis azole resistance was not observed. Two main Cyp51A-SNPs were found in azole-resistant isolates: Y119F and T329A. Aspergillus flavus was the dominant pathogenic species within the section Flavi with low levels of azole resistance. Distribution of resistant cases supports in host resistance selection rather than environmental selection. These findings highlight the need for further research on the ecological and molecular factors that influence resistance in A. flavus.