Investigating the Impact of Environmentally Relevant Imidazole Concentrations on the Antifungal Susceptibility and Community Composition of Soil Fungi
Abstract
Miconazole and clotrimazole are environmentally-persistent drugs that are entrained into crop soils through the application of biosolids. There is concern that environmental exposure to such azole antifungals, which inhibit fungal growth by disrupting the production of the fungal cell membrane component ergosterol, promotes resistance in clinically or agriculturally relevant fungi. Thus, either environmentally-relevant or excessive levels of these drugs were applied to microplots over ten years and compared with drug-free plots. Overall, ergosterol quantification, plates counts, and identification of >250 fungal isolates showed lower fungal counts and species richness in plots receiving excessive drug amounts. In addition, fungi from treated plots did not show increased resistance to a panel of medical and agricultural azole drugs in disk diffusion assays. Altogether, while the highly contaminated soils showed lower fungal counts, lower species richness, and fewer isolates highly-susceptible to miconazole, increased resistance to azoles was not evident at environmentally relevant concentrations.