Comparison Of Silver Nanoparticles On Probiotics And Non-probiotics

Purposes: Silver nanoparticles are new type inorganic antibacterial materials which synthesized based on nanotechnology.An increasing number of drug-resistant strains were appeared in recent years,such as silver nanoparticles are very rare which could as broad spectrum antibacterial agents.And they are widely applied in many industries,especially in food industry.However,in the process of human contact with silver nanoparticles,whether during the process of synthesis or using,silver nanoparticles may enter human body through the respiratory system,the digestive system,skin and other ways.Therefore,the potential toxicity of silver nanoparticles is gradually attracting more and more attention.At present,the research on the potential toxicity of silver nanoparticles are almost focused on the toxicity of normal human cells and experiments of animals in vivo.Intestinal flora is important symbiotic microbes in the human body,and their balance is closely related to human health.However,the effects of silver nanoparticles on human intestinal bacteria were rarely reported.Thus in this thesis,we studied the effects of silver nanoparticles on probiotics and non-probiotics,compared their inhibitory effects and discussed the mechanism of inhibitory effects of silver nanoparticles on bacteria.Contents and methods: We synthesize silver nanoparticles using liquid-phase reduction method.The silver nanoparticles were characterized by UV-vis spectroscopy,nanoparticle size analyzers,transmission electron microscope.In this study we used Lactobacillus casei,Lactobacillus bulgaricus,Escherichia coli,and Staphylococcus aureus as the research object.Using plate count method,live/dead staining of bacteria,bacterial growth curve,and scanning electron microscope observation method to study growth inhibition of silver nanoparticles on four types of bacteria.Through the analysis of pH changes in bacterial culture system,silver ions releasing,generation of reactive oxygen species and changes of cell membranepermeability,we analyzed mechanism of inhibitory effect of silver nanoparticles on probiotics and non-probiotics.Results:(1)The Ag NPs are spherical,single topography,good dispersion,which have typical Ag NPs absorption peaks on 400 nm.Its zeta potential is-19.23±0.68 mV and the mean hydrated particle diameter is 49.31 nm.(2)Through bacteriostatic experiment,we obtain the antibacterial activity of silver nanoparticles from high to low: L.casei? L.bulgaricus?E.coli?S.aureus.Staining results shows dead cells of probiotic is far more than non-probiotics.Morphological observations found the injury of E.coli and probiotics are more serious.Ag NPs treated led to the postponement of the logarithmic growth of bacteria and reduced concentrations of bacterial when finally reached the plateau.(3)The pH value of probiotic culture medium was reduced to 4.5 in the process of incubation.Then Ag NPs could induce more reactive oxygen species,release more Ag+,and finally led to probiotics inhibited more seriously by Ag NPs.And Ag NPs caused more serious damage to the cell membrane of probiotics.