Study On Antibacterial Activity And Mechanism Of Metal Ions

Metal ions, such as silver, zinc and copper, because of their broad-spectrum antibacterial properties, heat resistance, good dispersion and low drug resistance and applied to various implant materials and medical devices. However, as metal ionic antibacterial implant materials, how to make good bactericidal properties or anti-adhesion properties of medical devices, but without harming normal tissues or cells, which is always the focus of the dispute.In this paper, we studied minimum inhibitory concentration(MIC) and minimum bactericidal concentration(MBC) of silver, zinc and copper ions against Staphylococcus aureus and Escherichia coli by the plate colony counting method. We also investigated cell cytotoxicity of silver, zinc and copper ion by cell proliferation assay, cell morphology observation and half inhibitory calculation of IC50 concentrations. Therefore, we got the relationship between sterilization rate of metal ions concentrations and cytotoxicity results. The results showed that when the silver ion concentration in the range of 2.5 × 10-7 M ~ 10-6 M, zinc ion concentration range from 10-5 M ~ 10-4 M and copper ion concentration in the range of 10-5 M ~ 10-4 M, there had more than 90% of the bacteria sterilization rate against S.aureus and E.coli, and no cytotoxicity on L929. The results of optimal concentration of metal ions provide theoretical basis for the design of antibacterial materials.Although silver, zinc and copper ions as antibacterial agents are widely used in antibacterial biomaterials. But the sterilization mechanism has no unified conclusion, which is badly need researchers to solve. In this paper, transmission electron microscopy is used to observe the ultrastructure of bacteria, reactive oxygen species kit is used to detect active oxygen content. Finally, the bacterial genomic DNA results is used to judge bacterial nucleic acid level changes after the handling of the metal ion. The results showed that there may be three types of metal ions bactericidal mechanism:(1) metal ions are of positive charge, when they reach the microbial cell membranes, they can be strongly adsorbed by membrane with negative charge due to coulomb attractive force, and then penetrate the cell wall, resulting in cell walls rupture, all these finally result in the death of bacteria.(2) Metal ions as the catalytically active sites can stimulate water or oxygen in the air to produce hydroxyl radicals(-OH) and reactive oxygen ion(O2-), there by undermining the ability of bacteria propagation, resulting in the death of the bacteria, but does not change the level of nucleic acids in bacteria. In addition, this study found bacterial DNA integrity is not destroyed after metal ion treatment. That is to say, bacterial DNA maintains the integrity of the gene in the process of sterilization.As we all known, metal ions has good bactericidal properties, but silver ions is expensive and easily oxidized by light or heat, resulting in reduced antimicrobial effect. So it is meaningful that copper ions or zinc ions partially replace the role of the silver ions to reduce costs and improve performance. In this paper, we used the plate bacterial colony count method and live and dead staining method to research the synergistic bactericidal effect of metal ions, providing a theoretical basis for the design of new antibacterial materials.The results of this paper provide theoretical basis for the designer of antibacterial materials. Other researchers in our group used the concentration of metal ions which have good sterilization rate and without cell cytotoxicity. They designed titanium or tantalum metal grafting copper ions, which possess good antimicrobial properties but not cell cytotoxicity.