Because of the ever-increasing resistance of pathogenic microorganisms, requires new treatments. Bacterial resistance to silver is rare; therefore, this property can be used for antibiotic-resistant bacteria. In this study, the potential of extracellular production of silver nanoparticles by psychrotolerant strain of OSNP14 and antibacterial properties was investigated. The strain was cultured in TSB medium and incubated at 20 °C for 3 days. After time, the culture medium was centrifuged and 1 mM silver nitrate (1 M concentration) was added to the supernatant. Reduction of Ag+ to Ag0 was confirmed by the colour change of culture medium. The UV-visible and XRD spectroscopy were used to determine the purity and size of the nanoparticle. The antimicrobial property of silver nanoparticles was evaluated using microdilution method using ELISA. The pathogenic bacteria of Escherichia coli and Staphylococcus aureus were exposed to different concentrations of silver nanoparticles in Muller Hinton broth medium and incubated at of 37 °C for 24 hours. The results showed one peak (400-500 nm) was detected for silver nanoparticles in the UV-visible spectrometer indicated the presence of silver nanocrystals. This result was proved using the XRD method with nanocrystals size of 53 nm. Silver nanoparticles have a minimum inhibitory concentration (MIC) of 62.5 mg/l and 125 mg/l for Staphylococcus aureus and Escherichia coli, respectively. This study showed that psychrotolerant strains are suitable for nanoparticles production due to the physicochemical properties of nanoparticles including size, zeta potential, surface morphology and crystalline structure of the elements that can inhibit bacterial pathogens.

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