Occurrence of Aspergillus fumigatus azole resistance in soils from Switzerland.

Aspergillus fumigatus is a fungal species causing diverse diseases in humans. The use of azoles for treatments of A. fumigatus diseases has resulted in azole resistance. Azoles are also widely used in the environment for crop protection, which resulted in azole resistance. Resistance is primarily due to mutations in cyp51A, which encodes the target protein for azoles. Here we addressed the occurrence of azole resistance in soils from a vast part of Switzerland. We aimed to associate the use of azoles in the environment with the occurrence of azole resistance. We targeted sample sites from different agricultural environments as well as sites with no agricultural practice (natural sites and urban sites). Starting from 327 sites, 113 A. fumigatus isolates were recovered (2019-2021), among which 19 were azole-resistant (15 with TR34/L98H and four with TR46/Y121F/T289A resistance mutations in cyp51A). Our results show that azole resistance was not associated with a specific agricultural practice. Azoles could be chemically detected in investigated soils, however, their presence was not associated with the occurrence of azole-resistant isolates. Interestingly, genetic markers of resistance to other fungicides were detected but only in azole-resistant isolates, thus reinforcing the notion that A. fumigatus cross-resistance to fungicides has an environmental origin. In conclusion, this study reveals the spreading of azole resistance in A. fumigatus from the environment in Switzerland. The proximity of agricultural areas to urban centers may facilitate the transmission of resistant strains to at-risk populations. Thus, vigilant surveillance is required to maintain effective treatment options for aspergillosis.

Aspergillus fumigatus is ubiquitous and causes diseases in humans. Antifungal drugs, and especially azoles, are used to combat A. fumigatus. Azoles are widely used in the environment, which exposes A. fumigatus and results in azole resistance. Azole resistance was investigated in Switzerland.

Multistep drug intercalation: molecular dynamics and free energy studies of the binding of daunomycin to DNA.

Atomic-scale molecular dynamics and free energy calculations in explicit aqueous solvent are used to study the complex mechanism by which a molecule can intercalate between successive base pairs of the DNA double helix. We have analyzed the intercalation pathway for the anticancer drug daunomycin using two different methods: metadynamics and umbrella sampling. The resulting free energy pathways are found to be consistent with one another and point, within an equilibrium free energy context, to a three-step process. Daunomycin initially binds in the minor groove of DNA. An activated step then leads to rotation of the drug, coupled with DNA deformation that opens a wedge between the base pairs, bends DNA toward the major groove, and forms a metastable intermediate that resembles structures seen within the interfaces between DNA and minor-groove-binding proteins. Finally, crossing a small free energy barrier leads to further rotation of daunomycin and full intercalation of the drug, reestablishing stacking with the flanking base pairs and straightening the double helix.