Anticandidal Potential of Two Cyanobacteria-Synthesized Silver Nanoparticles: Effects on Growth, Cell Morphology, and Key Virulence Attributes of Candida albicans

Abstract

Candida albicans is an opportunistic human fungal pathogen responsible for 90–100% of mucosal and nosocomial infections worldwide. The emergence of drug-resistant strains has resulted in adverse consequences for human health, including numerous deaths. Consequently, there is an urgent need to identify and develop new antimicrobial drugs to counter these effects. Antimicrobial nanoagents have shown potent inhibitory activity against a number of pathogens through targeting their defense systems, such as biofilm formation. Here, we investigated the anticandidal activity of silver nanoparticles biosynthesized by the cyanobacterial strains Desertifilum sp. IPPAS B-1220 and Nostoc Bahar_M (D-SNPs and N-SNPs, respectively), along with that of silver nitrate (AgNO3), and examined the mechanisms underlying their lethal effects. For this, we performed agar well diffusion and enzyme activity assays (lactate dehydrogenase, adenosine triphosphatase, glutathione peroxidase, and catalase) and undertook morphological examinations using transmission electron microscopy. The effects of the three treatments on Hwp1 and CDR1 gene expression and protein patterns were assessed using qRT-PCR and SDS–PAGE assays, respectively. All of the three treatments inhibited C. albicans growth; disrupted membrane integrity, metabolic function, and antioxidant activity; induced ultrastructural changes in the cell envelope; and disrupted cytoplasmic and nuclear contents. Of the three agents, D-SNPs showed the greatest biocidal activity against C. albicans. Additionally, the D-SNP treatment significantly reduced the gene expression of Hwp1 and CDR1, suggestive of negative effects on biofilm formation ability and resistance potential of C. albicans, and promoted protein degradation. The mechanism involved in the biocidal effects of both D-SNPs and N-SNPs against C. albicans could be attributed to their ability to interfere with fungal cell structures and/or stimulate oxidative stress, enabling them to be used as a robust antimycotic agent.