Study On The Antimicrobial Mechanism Of Silver Nitrate And Silver Nanoparticles On Baceteria By Atomic Force Microscopy

AgNO3 and silver nanoparticles are proven to be the bacteriostatic agent with good antibacterial activity against bacteria,but its antibacterial mechanism has not been accurately determined.Atomic force microscopy(AFM)can provide unprecedented insight to visualize the structure of cell wall and cell membrane,track the dynamic changes of cells growth,division,or the interaction with drugs,and measure the surface mechanical properties of cells.In the past few decades,AFM has become a powerful tool in the study of microbiology.The nano-level imaging and the piconewton-level mechanical measurement will provide a better way to understand the structure and function of cell surface components.AFM will help to elucidate the interaction mechanism between AgNO3,silver nanoparticles and bacteria,and lay the foundation for the widespread use of AgNO3 and silver nanoparticles in the medical fields.In this thesis,the antibacterial mechanism of AgNO3 and silver nanoparticles on Escherichia coli and Staphylococcus aureus was investigated by AFM imaging and force curve measurement,assisted by the bioassays of static culture,growth curve and ?-galactosidase activity.The main results are as follows:1.After the action of AgNO3 on E.coli for 12 h,it could be observed that vesicles appeared on the cell surface,the rod-like structure collapsed,the contents leaked,the surface roughness(Ra)increased from 11.4 nm to 17.0 nm,.and the root mean square roughness(Rq)increased from 14.2 nm to 21.0 nm.The slope of force curve decreased from-1.40 to-1.74,the elasticity of cell surface decreased,the adhesive force increased by 1 nN,and the Young's modulus increased from 277 Mpa to 880 Mpa.The growth of E.coli was completely inhibited after cultivation for 48 h,and the permeability of cell membrane increased.2.After the action of AgNO3 on S.aureus for 12 h,depressions and breakages occurred on cell surface,contents leaked,Ra decreased from 16.4 nm to 12.5 nm,.and Rq decreased from 20.4 nm to 15.7 nm.The slope of force curve increased from-24.12 to-18.23,the elasticity of cell surface increased,the adhesive force increased by 42 nN,and the Young's modulus increased from 1812 Mpa to 882 Mpa.The growth of S.aureus was completely inhibited after cultivation for 4 h,moreover,the amount of cells was less than that of the control group after cultivation for 48 h,and the permeability of cell membrane increased.3.After the action of silver nanoparticles on E.coli for 12 h,the changes could be observed that the cell surface was collapsed and swelled,contents leaked,Ra decreased from 10.7 nm to 7.0 nm,.and Rq decreased from 13.7 nm to 8.8 nm.The slope of force curve decreased from-1.44 to-3.95,the elasticity of cell surface decreased,the adhesive force increased by 8 nN,and the Young's modulus increased from 334 Mpa to 3113 Mpa.The growth of E.coli was completely inhibited after cultivation for 48 h,moreover,the amount of cells was less than that of the control group for after cultivation 48 h,and the permeability of cell membrane increased.4.After the action of silver nanoparticles on S.aureus for 12 h,the changes could be observed that depressions and breakages appeared on the cell surface,contents leaked,Ra decreased from 15.9 nm to 13.9 nm,.and Rq decreased from 19.4 nm to 17.6 nm.The slope of force curve increased from-26.41 to-19.62,the elasticity of cell surface increased,the adhesive force increased by 38 nN,and the Young's modulus increased from 1797 Mpa to 1019 Mpa.The growth of S.aureus was completely inhibited for after cultivation 6 h,moreover,the amount of cells was larger than that of the control group after cultivation for 24 h,and the permeability of cell membrane remained essentially unchanged.