Hazard of agricultural triazole fungicide: Does cyproconazole induce voriconazole resistance in Aspergillus fumigatus isolates?

Background and Purpose: The present study aimed to evaluate the effect of cyproconazole, the most used fungicide in Iranian wheat farms, on the induction of voriconazole resistance in Aspergillus fumigatus isolates. Materials and Methods: A collection of ۲۰ clinical and environmental isolates were selected for investigation of the in vitro activity of fungicides. The minimum inhibitory concentrations (MICs) were determined by the documented broth microdilution method M۳۸-A۲ (CLSI, ۲۰۰۸). Induction experiments were performed and the possibly induced isolate(s) were subjected to antifungal susceptibility testing, sequencing of the CYP۵۱A promoter, and full coding gene. Furthermore, CYP۵۱-protein homology modeling and docking modes were evaluated using SWISS-MODEL (https://swissmodel.expasy.org/) and SEESAR software (version ۹.۱). Results: Among ۱۰ susceptible isolates, only one strain showed a high MIC value against voriconazole (MIC=۴μg/ml) after ۲۵ passages. Nevertheless, sequencing of the CYP۵۱A promoter and full coding gene did not reveal any mutations. Cyproconazole, which has three nitrogen atoms in the aromatic ring, coordinated to the iron atom of heme through a hydrogen bond contact to residue Lys۱۴۷ present in the active site of the A. fumigates Cyp۵۱ homology model. Conclusion: Cyproconazole is being applied extensively in wheat farms in Iran. According to the results, cyproconazole may not play a key role in the induction of azole resistance in the isolates through the environmental route. However, the potential ability of the fungicide to induce medically triazole-resistant strains over a long period of application should not be neglected.

Keywords:

Aspergillus fumigatus , Cyproconazole , Fungicide , Homology modeling , Wheat