Effect of non-antifungal agrochemicals on the pathogenic fungus Cryptococcus gattii

The chemical control of pests and weeds is employed to improve crop production and the quality of agricultural products. The intensive use of pesticides, however, may cause environmental contamination, thus altering microbial communities. Cryptococcus gattii is an environmental yeast and the causative agent of cryptococcosis in both humans and animals. Up to this day, the effects of agrochemicals on human pathogens living in nature are still widely unknown. In this work, we analyzed the susceptibility of C. gattii to nonfungicide agrochemicals (herbicides and insecticides). Microdilution and drug-combination susceptibility tests were performed for the herbicides flumioxazin (FLX), glyphosate (GLY), isoxaflutole (ISO), pendimethalin (PEND), and also for the insecticide fipronil (FIP). Moreover, these compounds were combined with the clinical antifungals amphotericin B and fluconazole. The MIC values found for the agrochemicals were the following: < 16 μg/ml, for flumioxazin; 128 to 256 μg/ml, for FIP, ISO, and PEND; and >256 μg/ml, for GLY. Synergistic and antagonistic interactions, depending on the strain and concentration tested, were also observed. All strains had undergone adaptation to increasing levels of agrochemicals, in order to select the less susceptible subpopulations. During this process, one C. gattii strain (196 L/03) tolerated high concentrations (50 to 900 μg/ml) of all pesticides assessed. Subsequently, the strain adapted to flumioxazin, isoxaflutole and pendimethalin showed a reduction in the susceptibility to agrochemicals and clinical antifungals, suggesting the occurrence of cross-resistance. Our data point to the risk of exposing C. gattii to agrochemicals existing in the environment, once it might impact the susceptibility of clinical antifungals.