Antibacterial effect of silver nanoparticles synthesized from the red algae Gracilaria gracilis

Silver nanoparticles (Ag-np) have high penetration and antimicrobial effect due to their high    surface-to-volume ratio. The aim of this study was to biosynthesize silver nanoparticles with red algae extract, Gracilaria gracilis, and to investigate their antibacterial activity against a number of standard and drug-resistant pathogenic bacteria.  First, Ag-np were synthesized. To confirm the structure and size of Ag-np, was used X-Ray diffraction spectroscopy, FE-SEM electron microscopy, and X-ray energy dispersive spectroscopy (EDS). The antimicrobial effects of algae extract on bacteria were determined by sequential dilution method. The size of nanoparticles under electron microscopy was between 12 and 46 nm. The nanoparticles were able to inhibit most of standard and antibiotic resistant bacteria, Ag-np at a concentration of 29 μg /ml, on the standard bacteria: S. typhimorium, E. coli, K. pneumonia and the clinically resistant bacteria, E. coli and           K. pneumonia, they had the most inhibitory effect. In contrast, standard and clinically resistant isolates of S. aureus and    standard strain S. pneumonia were resistant to Ag-np. The results of this research showed that the G. gracilis red algae as a bio-source that can be useful for green synthesis of silver nanoparticles at very low cost applications, these nanoparticles can be used as candidates for drug composition.