Antibacterial evaluation of sliver nanoparticles synthesized by polysaccharides from Astragalus membranaceus roots

This work introduced an eco-friendly approach for the synthesis of sliver nanoparticles (AgNPs) with a water-soluble fraction of polysaccharides extracted from the roots of Astragalus membranaceus (AMWP). AMWP mediated AgNPs (AMWP-AgNPs) were successfully synthesized using 1.0 mM AgNO3 and 1.25 mg/mL AMWP, reacting in aqueous environment at 25 °C for 6 h. The synthesized AMWP-AgNPs exhibited a broad surface plasmon resonance peak (SPR) at 445 nm in Ultraviolet-visible (UV–vis) spectrum, which was characteristic of a poly-dispersed AMWP-AgNPs. Transmission electron microscopy (TEM) and Dynamic light scattering (DLS) analysis revealed that the AMWP-AgNPs were almost spherical shaped with an average diameter of 65.08 nm. The antibacterial activities of AMWP-AgNPs were assessed on four strains of clinical isolated multidrug resistant (MDR) bacteria and four relative reference strains using modified agar disk diffusion and tetrazolium methods. All strains, especially the resistant strains, were significantly inhibited by AMWP-AgNPs at comparatively low concentration (minimum inhibition concentrations (MICs) ranging from 0.032 to 0.063 mg/mL). Therefore, we propose that the AMWP-AgNPs will have a great potential in anti-MDR bacterial applications.