Development of an In Vitro Electrical Impedance Model to Assess Cytotoxicity and Antifungal Efficacy of Aspergillus fumigatus

Aspergillus fumigatus causes fatal infections in immunocompromised individuals, with the increasing number of azole-resistant strains leading to high mortality rates. This study aimed to develop a novel in vitro model using electrical impedance to continuously evaluate interactions between A. fumigatus and human cells and antifungal agent efficacy. A. fumigatus conidia and human cell lines (THP-1 macrophages and A549 alveolar epithelial cells) were cultured. Electrical impedance and fluorescence were observed using the xCELLigence RTCA E-Sight system. Conidia were seeded at various multiplicity of infection (MOI) values, and cell damage was assessed. In addition, the inhibition of cell damage by A. fumigatus in response to antifungal agents was evaluated. The time needed for electrical impedance to fall by half in macrophages was 31.5 hours for MOI 0.1 and 14.1 hours for MOI 8. Therefore, higher conidial concentrations led to faster decreases in electric impedance, indicating increased cytotoxicity. Macrophages showed a gradual decrease in electric impedance with mycelial growth, whereas A549 cells displayed a rapid electric impedance decline after mycelial growth. Azoles and amphotericin B suppressed the electric impedance decrease above their minimum inhibitory concentration, while echinocandins resulted in a continuous electric impedance decrease regardless of concentration. This study demonstrated that electrical impedance constitutes an objective method for continuously evaluating the cytotoxicity of A. fumigatus and antifungal efficacy. This novel in vitro model offers a new standard for studying interactions between filamentous fungi and human cells. Further validation using clinical isolates and other fungi is required.