Potential synergistic antifungal activity of microbially synthesized silver nanoparticles and vitamin D3 against Candida albicans: In vitro and Galleria mellonella model studies.

Candida albicans poses a serious health threat, contributing to approximately 1.5 million deaths each year. Although azole drugs have been used to manage this pathogen, their effectiveness has been compromised by the emergence of drug-resistant strains. Therefore, silver nanoparticles (nano-Ag) and vitamin D₃ are being explored as complementary rather than direct antifungal agents. The present study aims to investigate the effects of microbially synthesized nano-Ag alone and with vitamin D3 against fluconazole-susceptible and fluconazole-resistant C. albicans. The broth microdilution method, checkerboard microdilution assay, hyphal formation inhibition, and gene expression analysis of key virulence genes were performed on C. albicans treated with microbially synthesized nano-Ag, either alone or combined with vitamin D3. Furthermore, the survival rate, haemocyte density, and microbial load in haemolymph were assessed in C. albicans-infected Galleria mellonella larvae after treatment with microbially synthesized nano-Ag alone and with vitamin D3. The results demonstrated that microbially synthesized nano-Ag exhibited synergistic and additive interactions with vitamin D3 against C. albicans. This study also revealed that the combination of microbially synthesized nano-Ag and vitamin D3 effectively inhibited hyphal formation and significantly downregulated the expression of SAP and HWP1 genes in C. albicans. In vivo experiments further demonstrated that this combined treatment enhanced larval survival, increased haemocyte density, and reduced microbial load in the haemolymph. Taken together, these findings underscore the potential of microbially synthesized nano-Ag with vitamin D3 as a promising synergistic treatment for C. albicans infections, particularly those resistant to fluconazole.