The Effect And Mechanism Of Ag@AgCl Against Salmonella Typhimurium Biofilm

In nature and human life, the majority of bacteria are attached to the surface of various organic or inorganic object. They are growing in the way of biofilm manner which are widely distributed. At the same time, bacterial biofilms have highly resistance against antibiotics. Their resistance to antibiotics is hundreds of times than planktonic bacteria. Currently, in order to solve the many problems caused by bacterial biofilms, the studies of how to inhibit the formation of bacterial have become research priorities in food, medicine, and materials science fields. Nowadays have studies shown that Ag@Ag Cl is a highly efficient photocatalyst that can effectively degrade organic pollutants which in water, but its effect on bacteria and bacterial biofilms are rarely reported. Furthermore, the attention of the most studies are focused on the development of these similar new materials. The exploration on the mechanism of photocatalytic material to inhibit and kill bacteria and biofilm formation on the molecular level are rarely. In addition, the traditional means of researching the interaction between biochemical material and bacteria are focused on the plate count(viability test), electron microscopy(bacterial surface morphology), DNA microarrays(changes in gene expression). But they all have some shortcomings such as complex operations, time-consuming and high cost. On this basis, we have adopted a Fourier transform infrared spectroscopy and quartz crystal microbalance to do a series of studies, the main contents are:Firstly, the Ag@Ag Cl photocatalyst which have highly photocatalytic activity was prepared and observed its inhibitory effect on the bacterial biofilm formation. First, the synthesized Ag@Ag Cl photocatalyst was characterized by UV-visible spectroscopy, XRD and FESEM. Subsequently we determined the minimum inhibitory concentration of Ag@Ag Cl for Salmonella typhimurium which have found that the MIC under visible light conditions and dark is 12.5mg/L and 100mg/L respectively. The salmonella typhimurium biofilm were successfully cultured in vitro by using the 96 microwell plate and glass sheet containing method. The crystal violet staining method and the silver staining method was used separately to semi-quantitative analysis and qualitative analysis on bacterial biofilm in order to observe the inhibitory effect of Ag@Ag Cl on bacterial biofilm. The conclusion is the amount of bacterial biofilm formation gradually decreased with the increase of Ag@Ag Cl concentration.Secondly, the method combines FT-IR and chemometrics has been studied the effect mechanism of Ag@Ag Cl on bacteria.The bacteria treated by the different concentration of Ag@Ag Cl can gather together respectively from the principal component score chart in the experiment indicating that the molecular components of bacterial cells has changed. This phenomenon indicates that the different damage degree of the bacteria, which the higher the concentration, the more serious damage. Moreover, The main components of the load chart found that the bacterial polysaccharide, lipid, DNA, protein structure changes after the action of, which suggests the Ag@Ag Cl hasa disproportionate impact on the bacterial cell membrane, cell wall, cytoplasm, nucleic acid.Thirdly, the initial adhesion properties of Salmonella typhimurium were observed after the impact of Ag @ Ag C. The QCM sensor device with good gas and liquid stability was established for the bacterial adhesion. Then we observe the adhesion situation of bacteria on the surface through QCM sensor device after the bacteria treated by the different concentration of Ag@Ag Cl. The experiment found that the bacterial has strong adhesive capacity when undamaged. Meanwhile, the bacterial flagella are damaged in different degree and the adhesion ability decreased gradually with the increase of concentration. In addtion, we also found that the overall structure of bacteria can complete and firmly adhere to the surface of QCM sensor device when has no Ag@Ag Cl effect on bacterial through FESEM. The bacterial surface is no longer smooth and exists clearly depression when the Ag@Ag Cl effect on bacterial, the phenomenon observed proves the bacterial has been damaged.The study results have shown that the methods combined infrared spectroscopy and chemometrics can well explain the mechanism of Ag@Ag Cl how to suppression and kill bacteria. This method can be considered to further promote in the future to further promote which can be used to study the bacterial treated by chemical material. We can observe the changes in the structure of the bacteria from the molecular level rather than just observe up from topography. The quartz crystal microbalance technology can be observed the changes of early bacteria adhesion on surface after treated by Ag@Ag Cl. We can use this method to screen new materials which can inhibit the bacterial adhesion. Its have great significance in biomedical fields.