Antifungal Potency of Biosynthesized Silver Nanoparticles Derived from Marine Diatoms Against Multidrug-Resistant Candida auris and Pichia kudriavzevii

Candida auris and Pichia kudriavzevii are emerging multidrug-resistant fungal pathogens that pose a significant threat to public health. The limited efficacy of conventional antifungals against these species has prompted the development of novel antifungal compounds. In recent years, silver nanoparticles (AgNPs) synthesized using marine diatoms have held promise as potent antifungal agents. In this study, three marine diatom species (Chaetoceros spp., Skeletonema spp., and Thalassiosira spp.) were utilized for the biosynthesis of AgNPs (Ag-DE/NPs). The biosynthesis was confirmed by a color change of the culture from colorless to brown and further validated by UV–vis spectroscopy, showing distinct surface plasmon resonance peaks at 425, 430, and 440 nm, respectively. Comprehensive characterization using FTIR, XRD, DLS, and SEM revealed the functionalized nature, crystalline structure, particle size, and surface morphology of the Ag-DE/NPs. The antifungal efficacy of these AgNPs was evaluated against 20 clinical isolates and 2 reference strains of C. auris and P. kudriavzevii, which exhibited high resistance to fluconazole. AgNPs synthesized from Chaetoceros spp. displayed the lowest geometric mean minimum inhibitory concentrations (0.23 µg/mL for C. auris and 0.19 µg/mL for P. kudriavzevii), showing a >250-fold greater potency compared to fluconazole and comparable efficacy to amphotericin B. Growth curve analysis and sorbitol supplementation assays indicated that Ag-DE/NPs disrupt fungal cell walls, while SEM imaging and ergosterol quantitation confirmed membrane damage and sterol depletion. These findings underscore the potential of Ag-DE/NPs, particularly those synthesized from Chaetoceros spp., as promising candidates for combating drug-resistant fungal infections.