Abstract
Silver nanoparticles (AgNPs) are considered a promising alternative to the use of antibiotics in fighting multidrug-resistant pathogens. However, their use in medical application is hindered by the public concern regarding the toxicity of metallic nanoparticles. In this study, rationally designed AgNP were produced, in order to balance the antibacterial activity and toxicity. A facile, environmentally friendly synthesis was used for the electrochemical fabrication of AgNPs. Chitosan was employed as the capping agent, both for the stabilization and to improve the biocompatibility. Size, morphology, composition, capping layer, and stability of the synthesized nanoparticles were characterized. The in vitro biocompatibility and antimicrobial activities of AgNPs against common Gram-negative and Gram-positive bacteria were evaluated. The results revealed that chitosan-stabilized AgNPs were nontoxic to normal fibroblasts, even at high concentrations, compared to bare nanoparticles, while significant antibacterial activity was recorded. The silver colloidal dispersion was further mixed with essential oils (EO) to increase the biological activity. Synergistic effects at some AgNP–EO ratios were observed, as demonstrated by the fractionary inhibitory concentration values. Our results reveal that the synergistic action of both polymer-stabilized AgNPs and essential oils could provide a significant efficiency against a large variety of microorganisms, with minimal side effects.
Highlights
Antibiotics have been very effective in controlling bacterial infections in the early part of the last century, being considered one of the most important findings in medical practice
With increasing concerns of microbial infections, there is a growing interest in the development of new, effective antimicrobial agents. The former strategy of combatting resisting microorganisms was based on the development of new antibiotics, but this way has been abandoned by many pharmaceutical companies due to financing and regulatory difficulties, aggravated by the rapidity with which the resistance to newly synthesized antibiotics is developed [2,3]
In order to evaluate the synergism between the AgNPs and essential oils, quantitative parameters of antimicrobial activity were determined by the minimum inhibitory concentration (MIC) method on selected bacterial strains, using AgNP–essential oil mixtures at various volumetric ratios
Summary
Antibiotics have been very effective in controlling bacterial infections in the early part of the last century, being considered one of the most important findings in medical practice. Nanoparticles with antibacterial properties have been extensively studied during the last decade [4], with particular interest in the mechanisms of action against the multidrug-resistant strains of bacteria [5] This has promoted research in the well-known activity of silver ions and silver-based compounds, including silver nanoparticles [6]. Common methods involve the chemical reduction of silver salts by different reducing agents such as NaBH4, sodium citrate, or ascorbic acid [13,14]. In such chemical processes, the nanoparticles tend to aggregate due to the high surface energy inherent to the synthesis. The rational design of novel AgNPs stabilized with biopolymeric compounds was utilized to ensure a stable, nontoxic metallic Ag nanostructure that combined with essential oils could generate an improved antibacterial efficiency
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