Improving The Antibacterial Efficiency Of Melittin With Graphene Oxide Nanomaterials

Antimicrobial peptides(AMPs)are expected to provide a fundamental solution to the increasingly serious problem of bacterial resistance.Melittin is one of the most representative AMPs.It will make pores on membranes,leading to the leakage of cellular contents and final cell death.Therefore,it has the function of broad-spectrum sterilization.However,a high critical concentration is needed for melittin to realize its bactericidal function,which seriously hinders its clinical use.On the other hand,graphene oxide(GO)has good biocompatibility and has been widely investigated as drug carriers,antimicrobial agents,etc.It could mechanically perturb cell membranes in a similar way as melittin.This mechanism of similarity inspires us to use graphene oxide as an assistance,so as to enhance the antibacterial efficiency of melittin at low concentrations.In this thesis,we made full use of the similarity between GO and melittin on membrane actions,to improve the antibacterial efficiency of melittin via pretreatment with GO at quite low GO concentrations.The work mainly includes three parts:(1)With the ca lce in-e ncaps u lated giant unilamellar vesicle(GUV)model,the minimum critical concentrations of melittin to induce calcein leakage from inside GUVs to outside,were obtained both without or with GO pretreatment;Obvious improvement on membrane activity of melittin was observed with GO.(2)With Gram-negative and Gram-positive bacteria,the minimum inhibitory concentration(MIC)values of melittin,both without or with GO pretreatment at various concentrations,were acquired;Obvious improvement on antimicrobial efficiency and reduction of cytotoxicity of melittin were realized with GO pretreatment,especially with low GO concentrations.(3)The underlying mechanism of GO influence on the membrane actions of melittin was analyzed,based on combining experiments including frozen transmission electron microscopy,atomic force microscopy,fluorescence recovery after photobleaching,as well as computer simulations.This work demonstrates an effective method to improve the antibacterial efficiency and reduce the cytotoxicity of AMP melittin,which not only has important research value for materal science and biology,but also is of great significance for biomedical design of novel antimicrobial agents.