Antibacterial Mechanism Of Silver Nanoparticles On Bacteria

Objective: Nanotechnology has gained tremendous research attention as a tool to explore medicine. Since ancient time, silver and its compounds have strong inhibitory and bacterial effects as well as a broad spectrum of antimicrobial activities for bacteria, fungi, and virus. Compared with other metals, silver shows higher toxicity to microorganisms while exhibiting lower toxicity to mammalian cells. Then silver nanoparticles(Ag NPs) have drawn people’s attention as an potential antibiotic effect. Programmed cell death(PCD), defined as an active process that results in cell suicide, is an essential mechanism in eukaryotic organisms. Recently a growing volume of work has illustrated that prokaryotes are capable of exhibiting hallmarks of programmed cell death. In previous study, the antibacterial mechanism of Ag NPs has only been partially understood. In order to understand the antibacterial activity and acting mechanism of Ag NPs deeply, we elucidate this mechanism in the view of bacterial apoptosis for the first time.Methods: A. Transmission electron microscope(TEM) was used to testing the characterization of Ag NPs solution. B. Optical density(OD) and Colony-Forming Units(CFU) were used to detecting the antibacterial effect of Ag NPs. C. Agarose gel electrophoresis was ued to analyzing the effect of Ag NPs to bacterial genome DNA. D. Flow cytometry analysis was used for the detection of dead bacteria. E. Transmission electron microscope(TEM) was used for the observation of bacterial morphology treated with Ag NPs. F. Flow cytometry analysis was used to analysis the bacteria apoptosis. G. Brd U ELISA was used to study bacterial proliferation.Results: A. The solution we used in our study is Ag NPs. And the average size of Ag NPs is about 5~10nm.B. E. coli cells are lagged to growth when exposed with Ag NPs. And the rate of bacterial growth becomes delayed. C. The amount of the genome DNA of E. coli treated with Ag NPs is less than the control group. Ag NPs can reduce the amount of genome DNA of E. coli. D. The percentage of bacteria staining with PI is increasing when we treated E. coli with Ag NPs. It means that the percentage of dead bacteria treated with Ag NPs is increased. But this increasing trendency is not proportional to the concentration of Ag NPs. E. There are several electron dense granules in the centre of E. coli. But bacterial membrane and wall don’t have physical damage when co-cultured with Ag NPs. F. Flow cytometry analysis showed that percentage of apoptosis bacteria is increased. And this increasing trendency is statistical significance. G. The number of newborn bacterial DNA is found to be significantly decreased when exposed with Ag NPs. Bacterial proliferation is significantly inhibited in the presence of Ag NPs.Conclusions: In this study, we prove that Ag NPs can simultaneously induce apoptosis and inhibit new DNA synthesis in the cells in a positive concentration-dependent manner. This study presents the first induction of apoptosis in these bacteria by Ag NPs in this field. Our findings may provide a new strategy for the use of silver nanoparticles in antibacterial applications...