Phytosynthesis of Silver Nanoparticles: Size-Dependent Antimicrobial Activity and Application Potential

Silver nanoparticles (AgNPs) are among the most widely used type of nanoparticles due to their antimicrobial properties. While their application in disease treatment is well established, less is known about their ecological effects after they are released into ecosystems, where they may affect microorganisms and disrupt ecological balance. A green synthesis using Sambucus nigra fruit extract was applied to prepare AgNPs of two sizes, and their interactions with Brevundimonas vesicularis USM1, Pseudarthrobacter oxydans USM2, Pseudomonas putida USM4, Escherichia coli ATCC 10536, Staphylococcus aureus ATCC 25923, and Pseudomonas aeruginosa ATCC 27853 were examined. The nanoparticles were characterized by UV–Vis, TEM, and DLS, and microbial growth was assessed using microplate assays and colony enumeration. No significant inhibition of E. coli ATCC 10536, S. aureus ATCC 25923, or P. aeruginosa ATCC 27853 was observed in the presence of small (22 nm) or large (66 nm) AgNPs. Growth inhibition occurred in P. oxydans USM2 and P. putida USM4 exposed to small AgNPs, and in B. vesicularis USM1, P. oxydans USM2, and P. putida USM4 exposed to large AgNPs. The strain-specific responses indicate a size-dependent impact on bacteria, suggesting potential effects on microbiome structure and function. This study provides insights supporting environmental risk evaluation and safer-by-design development of AgNP-based materials.