Chitosan-silver nanocomposites: promising alternatives for combating azole-resistant Aspergillus fumigatus.

Background: The emergence of azole-resistant strains of Aspergillus fumigatus presents a significant challenge in clinical and settings, necessitating the development of alternative antifungal strategies. Chitosan-silver nanocomposites (Chi-AgNPs) have emerged as promising candidates due to their dual antimicrobial mechanisms and enhanced physicochemical properties. Objectives: This study aimed to evaluate the synthesis, characterization, antifungal properties, and low toxicity in an invertebrate model of Chi-AgNPs compared with those of chitosan and silver nanoparticles (AgNPs) alone, particularly against azole-resistant A. fumigatus. Methods: Chi-AgNPs were synthesized via a chemical reduction method and characterized using particle size analysis, ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Antifungal efficacy was assessed through minimum inhibitory concentration (MIC), minimum fungicidal concentration (MFC), microbial growth curves, and in vivo tests using Galleria mellonella larvae. Reactive oxygen species (ROS) generation and fungal cell wall deformation were analyzed to explore the antifungal mechanism. Results: Compared with chitosan and AgNPs alone, Chi-AgNPs exhibited superior physicochemical properties, with smaller and more uniform particle sizes (average: 212.5 nm) and improved dispersion stability based on immediate characterization data. The MIC and MFC of Chi-AgNPs (8-16 μg/mL and 128 μg/mL, respectively) were significantly lower than those of chitosan and AgNPs (128 μg/mL and >256 μg/mL, respectively). Compared with AgNPs, Chi-AgNPs induced higher ROS levels (p < 0.05) and were associated with more severe fungal cell wall damage. In vivo, the Chi-AgNPs-treated fungus-infected group presented the lowest mortality in G. mellonella larvae (p < 0.05), demonstrating superior antifungal activity and low toxicity in an invertebrate model. Conclusions: This study highlights the potential of Chi-AgNPs as promising alternatives to combat azole-resistant fungal infections. These findings provide a foundation for further development of Chi-AgNPs as novel antifungal agents with broad applicability.