Nanosilver, in the form of colloidal silver, has been used for many years. In recent years, the development of efficient green chemistry methods for the synthesis of metal nanoparticles by organisms has become a major focus of researchers. The different forms of nanoparticles prepared by green synthesis using plants are dependent on the structure as well as the potential reactions of molecules present in plant extracts. These forms of nanoparticles can exhibit antibacterial activity to any bacterial strain. The surface of silver nanoparticles (AgNPs) prepared by green synthesis using plants is modified with polyphenols, terpenoids and flavonoids that increase their antibacterial activity. Five types of AgNPs using inorganic synthesis as well as five types of AgNPs using green synthesis were successfully prepared. The AgNPs generated by inorganic synthesis differed in various concentrations of reducing agent (NaBH4, gallic acid). In addition, the AgNPs prepared by green synthesis are easily identified according to the plant extract entering into the synthetic reactions. Extracts of C. sinensis (green tea 1 and 2), T. erecta (Marigold), H. perforatum (St.John’s wort) and A. cepa (onion) were utilised for the green synthesis. Green synthesized AgNPs had a higher ability for quenching of radicals. Antibacterial activity of AgNPs was determined on bacterial cultures S. aureus and E. coli. AgNPs synthesized using green tea showed the highest antibacterial activity which was for S. aureus 96 % and for E. coli 95 %. The changes in bacterial biochemical parameters were also determined. AgNPs synthesized using St. John’s wort caused the highest numbers of biochemical changes (9 cases) in comparison with control. Changes in bacterial biochemical parameters due to effect of AgNPs is a significant discovery which will be worth of further investigation.Keywords: Nanosilver, antibacterial activity, Staphylococcus aureus, Escherichia coli
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