The antibacterial effect of different sizes of silver nanoparticales on Escherchia coli isolates and their plasmid pattern

Objectives: Silver nanoparticles as an alternative to antibiotics are in consider in recent years. It seems that sizes may affect their antibacterial properties. The present study aimed to investigate the effect of different sizes of silver nanoparticles on Escherchia coli isolates and their plasmid pattern.Materials Methods: Twenty five Escherchia coli isolates from dog fecal samples, were identified. Their plasmid pattern determined using alkaline lysis method. MIC and MBC of the isolates determined against different sizes of 20,40 and 70 nm silver nanoparticles at concentrations of 500-1000 µg/ml. The plasmid pattern of all isolates determined after the effect of different sizes of silver nanoparticles also.Results Conclusion: The concentrations of 500,550,600,650,700,750 µg/ ml of different sizes of silver nanoparticles had no antibacterial effect on Escherichia coli and in fact, all the isolates showed sensitivity in the concentrations higher than 800 µg/ mL.The results showed that the antibacterial effect of silver nanoparticles with different of sizes 20, 40 and 70 nm had no significant differences. In spite the different sizes of silver nanoparticles had different effect on plasmid pattern of the isolates. As it can be concluded that by reducing the sizes of silver nanoparticles, their effect on plasmid pattern were more obvious.