Pesticide behavior in paddy fields and development of azole-resistant Aspergillus fumigatus : Should we be concerned?

Tricyclazole as a common fungicide wildly used to control rice blast disease in the Asian country may induce azole resistance in Aspergillus fumigatus isolates. The main reason of the acquired azole resistance is probably environmental exposure through wide fungicide use in agriculture. The present study was conducted with the aim of investigating the current status of the azole-resistant A. fumigatus obtained from the paddy fields with exposure to tricyclazole. A total of 108 soil samples were collected from four different locations of paddy fields in Mazandaran Province, Iran. Pure fungal colonies were initially identified based on the conventional tools, and then reconfirmed by using DNA sequencing of the partial ß-tubulin gene. In addition, the in vitro antifungal susceptibility was determined using the Clinical and Laboratory Standards Institute document (CLSI) M38-A2. The identification of the mutations in the CYP51A gene was accomplished by the implementation of the polymerase chain reaction amplification assay on the selected isolates. Overall, 31 of 108 (28.7%) isolates were identified as A. fumigatus, four (3.7%) of which were recognized as azole-resistant with MICs of itraconazole ≥8μg/ml and voriconazole ≥4μg/ml. Only two out of the four azole-resistant A. fumigatus isolates harboured TR34/L98H variant and the other two isolates were identified as azole-resistant without any CYP51A gene mutations. However, other point mutations (TR46/Y121F/T289A) were not detected in the CYP51A gene. The high molecular structure similarity between environmental and medical triazoles may result in the selection of resistance mechanisms. Nonetheless, one might conclude that tricyclazole with different molecular structures against medical azoles induces azole-resistance in A. fumigatus isolates. The behavior of such pesticides as tricyclazole in the rice paddy fields would have an effective role in the development of azole-resistance that requires detailed information.