Biosynthesis of Silver Nanoparticles from Citrobacter freundii as Antibiofilm Agents with their Cytotoxic Effects on Human Cells

Background: Nanomaterials have recently been identified for their potential benefits in the areas of medicine and pharmaceuticals. Among these nanomaterials, silver nanoparticles (Ag-NPs) have been widely utilized in the fields of diagnostics, antimicrobials, and catalysis. Objective: To investigate the potential utility of Citrobacter freundii in the synthesis of silver nanoparticles (Ag-NPs), and to determine the antimicrobial activities of the Ag-NPs produced. Methods: Aqueous Ag+ ions were reduced when exposed to C. freundii extract and sunlight, leading to formation of AgNPs. Qualitative microanalysis for the synthesized Ag-NPs was done using UV-vis spectrometry, energy dispersive X-ray analysis (EDX), and scanning and transmission electron microscopy. The hydrodynamic size and stability of the particles were detected using dynamic light scattering (DLS) analysis. The Ag-NPs’ anti-planktonic and anti-biofilm activities against Staphylococcus aureus and Pseudomonas aeruginosa, which are two important skin and wound pathogens, were investigated. The cytotoxicity on human dermal fibroblast cell line was also determined. Results: Ag-NPs were spherical with a size range between 15 to 30 nm. Furthermore, Ag-NPs displayed potent bactericidal activities against both S. aureus and P. aeruginosa and showed noticeable anti-biofilm activity against S. aureus biofilms. Ag-NPs induced minor cytotoxic effects on human cells as indicated by a reduction of cell viability, a disruption of plasma membrane integrity, and apoptosis induction. Conclusion: Ag-NPs generated in this study might be a future potential alternative to be used as antimicrobial agents in pharmaceutical applications for wound and skin related infections.