Mechanistic study of antibacterial activity of biologically synthesized silver nanocolloids

Aqueous silver nanocolloids were synthesized using single step and completely green biosynthetic method employing aqueous leaf extracts of Paederia foetida as both the reducing and capping agent. Crystalline silver nanoparticles (AgNPs) having average diameter (8.9 ± 3.6) nm have been obtained. The nanocolloids are very stable and no precipitation was observed in 6 months. The absorption spectra of colloidal silver nanoparticles showed characteristic surface plasmon resonance (SPR) peak centered at a wavelength of 424 nm. The activity of the AgNPs colloidal suspension as an antibacterial agent against both gram negative (Shigella dysenteriae, Salmonella infantis, Vibrio parahaemolyticus and Escherichia coli) and gram positive (Staphylococcus aureus) bacteria was investigated following MIC as well as disc diffusion technique. Good antibacterial activity was found against all test bacteria. In-vitro and in-vivo DNA damage assay was performed by silver nanocolloid. Interestingly silver nanocolloid showed no genotoxic effect and this results lead to conclude that inhibition of bacterial growth occurred without any DNA damage by silver nanoparticle.