The Antibacterial Activity of Silver Nanoparticles against Pathogenic Bacteria is dependent on their Size, Shape, and Surface Properties.
The global increase in antimicrobial resistance (AMR) has led researchers to focus on silver nanoparticles (AgNPs) as potential antimicrobial agents. The present study used a multi-synthesis approach to obtain AgNPs of different size, shape, and surface properties (SSSP), and compared the effect of SSSP on the antibacterial activity of these AgNPs in combination with antibiotics. The two plant-synthesized quasi-spherical AgNPs (7.36 nm, 12.53 nm) showed better antimicrobial activity against multiple antibiotic-resistant (MAR) bacteria compared to microbially-synthesized quasi-spherical AgNPs (11.71 nm) or the larger chemically-synthesized spherical (17.65 nm) and hexagonal AgNPs (57.36 nm). When these plant-synthesized AgNPs were used along with antibiotics as silver nanoparticle-antibiotic combinations (SACs) and tested against vancomycin-resistant Staphylococcus aureus (VRSA) and MAR Acinetobacter baumannii (MAB), the smaller fatty acid-capped AgNPs showed better synergistic antibacterial activity than the larger protein-capped AgNPs. The AgNPs did not show any in-vitro cytotoxicity against normal mammalian Vero cells at effective antibacterial concentrations. The SACs displayed potent anti-biofilm activity against VRSA and MAB and caused leakage of the cytoplasmic contents, suggestive of loss of membrane integrity of the bacterial cells. The anti-biofilm activity of the SACs suggests that the plant-based AgNPs might be able to reduce pathogenesis of even highly resistant bacteria. Thus, the present study indicates that by modifying SSSPs of AgNPs, it may be possible to generate effective AgNP-based antimicrobial agents against highly resistant microorganisms.