Biosynthesis of Ag nanoparticles and Origanum vulgare Essential Oil/Ag Nanoparticles Nanoemulsion and Evaluation of Their Antibacterial Activity Against Escherichia coli O157:H7

In the present study, we synthesised Origanum vulgare essential oil/Ag nanoparticles nanoemulsion with a spontaneous emulsification method. First, Ag nanoparticles (AgNPs) were synthesised via a green method and these particles were then used as the aqueous phase of the nanoemulsions. Origanum vulgare essential oil (EO) exhibits a broad-spectrum antimicrobial activity against foodborne microorganisms like Escherichia coli O157:H7 so, it was used to preparing the nanoemulsion. Scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), UV-Vis spectroscopy confirmed the formation of AgNP and dynamic light scattering (DLS) was used to measuring the particle size and nanoemulsion droplet size. Finally, we investigated the antibacterial activity of AgNPs, Origanum vulgare EO and Origanum vulgare EO/AgNPs nanoemulsion against E. coli O157:H7 via inhibition zone method.Our results showed that bacterial inhibition zones of AgNPs were increased in a dose -dependent manner and Origanum vulgare EO (100%) had a great antibacterial activity against E. coli O157:H7 but its antibacterial activity was drastically decreased at 12.5% which was the concentration that used in the emulsion. As expected, nanoemulsion showed greater inhibition zones than AgNPs and EO(12.5%). The antibacterial activity of nanoemulsion is higher than its active components AgNPs and Origanum vulgare EO (12.5%) in which produced the largest E. coli O157:H7 inhibition zones (19.67 mm) within all the compounds (P<0.05).

Keywords:

nanoemulsion , nanoparticles , Origanum vulgare , essential oil , green synthesis