Antibacterial and Antifungal Properties of Silver Nanoparticles-Effect of a Surface-Stabilizing Agent

Abstract

The biocidal properties of silver nanoparticles (AgNPs) prepared with the use of biologically active compounds seem to be especially significant for biological and medical application. Therefore, the aim of this research was to determine and compare the antibacterial and fungicidal properties of fifteen types of AgNPs. The main hypothesis was that the biological activity of AgNPs characterized by comparable size distributions, shapes, and ion release profiles is dependent on the properties of stabilizing agent molecules adsorbed on their surfaces. Escherichia coli and Staphylococcus aureus were selected as models of two types of bacterial cells. Candida albicans was selected for the research as a representative type of eukaryotic microorganism. The conducted studies reveal that larger AgNPs can be more biocidal than smaller ones. It was found that positively charged arginine-stabilized AgNPs (ARGSBAgNPs) were the most biocidal among all studied nanoparticles. The strongest fungicidal properties were detected for negatively charged EGCGAgNPs obtained using (-)-epigallocatechin gallate (EGCG). It was concluded that, by applying a specific stabilizing agent, one can tune the selectivity of AgNP toxicity towards desired pathogens. It was established that E. coli was more sensitive to AgNP exposure than S. aureus regardless of AgNP size and surface properties.

Keywords: Candida albicans; Escherichia coli; Gram-negative bacteria; Gram-positive bacteria; Staphyloccus aureus; biocidal properties; minimum bactericidal concentration (MBC); minimum inhibitory concentration (MIC); pathogenic fungi; silver nanoparticles; surface properties.

Figure 1

Extinction spectra of diluted AgNP suspensions prepared with the use of (a) sodium borohydride (SB); (b) trisodium citrate (TC); (c) selected antioxidants and glucose (GL); (d) inorganic compounds.