Emergence of a Pathogenic Fungus Resistant to Triazole Antifungal Drugs

Over the past 20 years, emerging antifungal resistance has been observed in the human pathogen, Aspergillus fumigatus, and is responsible for serious infections. Resistance in this pathogenic fungus is mainly due to the unintended impact of triazole fungicides widely used in the environment to protect crops and materials from destroying fungi. A. fumigatus is naturally present in the environment and will thus be widely exposed to fungicides, which, through selection pressure, will favour strains that have become resistant. These fungicidal compounds have a chemical structure similar to that of medical compounds, thus rendering them inactive for the treatment of an infection in humans with a resistant strain. A. fumigatus does not cause infections in crops yet fungicidal compounds with activity against this widely present fungus select for an unintended cross-resistance. Therefore, it is important to understand the phenomena leading to resistance in the environment.

In this chapter, we first reviewed resistance mechanisms that have been described, both occurring under medical treatments and those rather attributed to environmental fungicidal use. We have detailed its spread from its probable origin in Europe to its current global distribution. Then, a focus on environmental contributing factors leading to resistance was done and in particular the cross-disciplinary use of azoles. We defined what can be considered as a hotspot of resistance selection and discussed the possible abiotic and biotics factors in soils implicated in the resistance emergence. Finally, we have considered various possibilities to stop the increase of this phenomenon: limit the uncontrolled spread of fungicides in the environment on the one hand and to reduce the exposure of fungicides on the other hand.