Biogenic Synthesis and Characterization of Silver Nanoparticles Using Some Medical Plants and Evaluation of Their Antibacterial and Toxicity Potential

Background: Silver nanoparticles (AgNPs) are employed in various applications in the areas of catalysis, optoelectronics, detection and diagnostics, antimicrobials, and therapeutics. Objective: The aim of this work was to study the antimicrobial activity of aqueous and methanolic leaf extracts of Thymus vulgaris and Urtica dioica and biologically prepared silver nanoparticles, as single or in combination treatments, against Escherichia coli and methicillin-resistant Staphylococcus aureus isolates. Methods: The minimum inhibitory concentration (MIC) was quantified by using a microdilution method in sterile 96-well microtiter plates. The assessment of the toxicity of AgNP solutions was evaluated on human blood lymphocyte cells. Results: The results of this study revealed that all AgNP solutions have the lowest MIC values against the bacterial isolates in relation with the methanolic and aqueous extract solutions. However, the results showed that the increasing AgNP concentration was a critical factor influencing the interaction between AgNPs and the human lymphocytes. Conclusions: The cytotoxicity of nanoparticles increased significantly (P < 0.05) at high concentrations. In addition, the biosynthesized AgNPs have an increased antimicrobial activity against all tested bacterial isolates. Highlights: AgNPs have been recognized as an effective antimicrobial agent that exhibits low toxicity in humans and has diverse in vitro and in vivo applications.