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چکیده
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Silver nanoparticles (AgNPs) are among the most effective antimicrobial agents that are used in the medi- cine and pharmaceutics. During the past decades, metal nanoparticles synthesis through application of the biological meth- ods has increasingly been used, as the biologically synthesized particles are mostly non-toxic as well as effective. Objectives: The main goal for undertaking the present investigation was to evaluate the extracellular synthesis of the AgNPs by a native thermophilic Bacillus Sp . AZ1 that was isolated from a hot spring in Ardebil province. Subsequently the antimicrobial potentials of the nanoparticle was evaluated against several human pathogenic organisms. Materials and Methods: The biosynthesized AgNPs were confirmed visually by appearance of a dark brown color for- mation in the mixture as well as silver surface plasmon resonance band by using UV-Visible spectroscopy. The AgNPs were further characterized by SEM, EDX and TEM. The antimicrobial activity of the AgNPs was investigated using Salmonella typhi , Escherichia coli , Staphylococcus epidermis , and Staphylococcus aureus , by applying disk diffusion method. Results: Identification of the strain AZ1 by the 16S rRNA sequence analysis showed 99% sequence homology between this strain and B. licheniformis . The obtained UV-Visible spectrum of the aqueous medium containing silver ion, showed a peak at 425 nm which indicates a correspondence to the plasmon absorbance of the silver nanoparticles. The biosynthe- sized AgNPs were found to be in the size range of ~7-31 nm with spherical the shape. Studies regarding the antibacteri- al effect of the particles showed the highest inhibitory effect against the two strains; E . coli , and S . typhi , respectively. Conclusions: Our study presents a simple green synthesis process for the production of an extracellular nanoparticles which is environmental friendly. Biosynthesis of the AgNPs by a thermophilic bacillus from the hot spring (Qeynarjeh, Ard
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