Antimicrobial effects of green-synthesized silver nanoparticles using thyme extract against Salmonella Typhimurium and Escherichia coli in yoghurt

This study was aimed to synthesize and characterize silver nanoparticles (AgNPs) prepared by mixing of both 10 − 1 M Ag and water-based extract (1:10 v/v; Ag/extract) obtained from the leaves of the Thymus ( Origanum onites ) plant by green methods. After synthesis, the properties of AgNPs were investigated by various characterization techniques, such as surface plasmon resonance (SPR), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). As a result of the synthesis, it was observed that the AgNPs had an average size of 47 nm and their shapes were triangular, hexagonal and spherical. The antimicrobial activity was evaluated against on Salmonella Typhimurium, Escherichia coli and the yoghurt starter cultures Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus. It was found that as the AgNPs concentration increased, the inhibition zones also increased, indicating a strong inhibitory effect at higher concentrations. Even if the most diluted AgNPs (10:90 v/v; AgNPs synthesized from 10 − 1 M Ag solution /phosphate-buffered saline) were added to yoghurt media, it was determined that they have prevented the growth of pathogens while preserving the activity of starter cultures starting from the third day.