Acquired triazole-resistance of Aspergillus fumigatus in soil and earthworm guts exposed to propiconazole and difenoconazole at field-realistic concentrations

Abstract Triazole-resistance in Aspergillus fumigatus has been frequently found in agricultural soils. We determined if triazole-resistance in A. fumigatus can be acquired in soil and earthworm guts after exposure to environmentally relevant concentrations of formulated propiconazole (FPRO) and difenoconazole (FDIF). Acquired triazole-resistance was found in two strains of A. fumigatus after exposure to 2.5 mg/L of FPRO and three strains of A. fumigatus after induction by 0.1–2.5 mg/L of FDIF for 40 d in liquid medium. Resistance development depended upon exposure time and substrate concentration. There were one, three, and two resistant strains of A. fumigatus in soils receiving FPRO, FDIF, and their combination, respectively. Resistance was identified in two strains of A. fumigatus isolated from the guts of earthworms exposed in soils contaminated by FDIF and two strains of A. fumigatus isolated from the guts of earthworms exposed to the combination of FDIF and FPRO. We conclude that normal applications of FPRO, FDIF, and their combination are likely to induce triazole-resistance in A. fumigatus in agricultural fields. Earthworms may act as disseminators of triazole-resistant A. fumigatus.