Antibacterial Activity And Antibacterial Mechanism Of Plant Extracts

In the process of production,transportation and storage of fresh agricultural products,it is easily corrupted due to the infection of food spoilage bacteria and pathogenic microorganisms.Furthermore,food spoilage bacteria and pathogenic microorganisms not only produce corruption stench and odor during growth and reproduction,but also generate some toxins,leading to food poisoning.The research and development of plant preservatives with natural high efficiency and nontoxic spectrum instead of chemical preservatives has become a highlight in preservation of fresh agricultural products by using Chinese abundant plant resources.In this study,a kind of Paeonia suffruticosa Andr.flower buds with the best antibacterial effect was selected from twenty-eight plant extracts.The aim of this study was to investigate its antibacterial activity and analysis its main chemical constituents.The antibacterial mechanism of Paeonia suffruticosa Andr.buds extract against Staphylococcus aureus,Pseudomonas aeruginosa and Escherichia coli O157:H7 were investigated.Twenty-eight plant extracts were screened for potential antibacterial activity against Staphylococcus aureu,Escherichia coli O157:H7,Pseudomonas aeruginosa,Penicillium Chrysogenum and Aspergillus niger by the diameter of the inhibition zone.It was found that Paeonia suffruticosa Andr.flower buds had the best antibacterial effect in the twenty-eight plants extracts,which had strong inhibitory effect on bacteria and yeast,and it also has certain inhibitory effect on mold.Meanwhile,the extraction method was optimized to obtain the Paeonia suffruticosa Andr.flower buds with high antibacterial.And UPLC-MS was used to analyze its components,sixteen main chemical components were identified,including three phenolic acids,four flavonoids three monoterpene glycosides and six gallotannins.The antimicrobial activity of Paeonia suffruticosa Andr.flower buds were further investigated by agar diffusion assay,microdilution method and growth curves method.The results showed that the minimum inhibition concentration and minimum bactericide concentration of Paeonia suffruticosa Andr.flower buds against tested bacterial strains were in the range of 1.56-3.13 mg·mL^-1 and 6.25-12.5 mg·mL^-1,respectively,which belongs to the highly effective plant bacteriostatic agent.The other characteristics of Paeonia suffruticosa Andr.flower buds were investigated.The results showed that Paeonia suffruticosa Andr.flower buds had a wide range of pH,high temperature resistance and UV stability,which had excellent properties and potential practical application prospects.The antibacterial mechanism was investigated by analyzing membrane fatty acid composition,membrane protein amino acid residue fluorescence spectra,membrane fluidity,membrane permeability and the changes in cell morphology.The results showed that the relative proportions of linear saturated and trans-monounsaturated fatty acids in the cell membrane of S.aureus increased by 23.67 and 27.87%at MIC and MBC,respectively,while the relative proportions of branched saturated and cis-monounsaturated fatty acid decreased by27.16 and 32.64%.The fluorescence intensity of membrane proteins amino acid residues Phe,Trp and Tyr reduced,and the maximum emission wavelength shifted significantly with the increase of the concentration of the extracts,indicating that Paeonia suffruticosa Andr.flower buds bound to the membrane and resulting in the changes in the structure and conformation of membrane proteins,which lead to the decrease of membrane fluidity and membrane dysfunction.The fluorescence intensity of PI and NPN increased significantly,indicating Paeonia suffruticosa Andr.flower buds destroyed the integrity of the membrane and increased the permeability of the cell membrane,leading to the leakage of intracellular substances.In addition,the DNA fluorescence spectrum was quenched obviously and the agarose gel electrophoresis strip was shallow in the nucleic acid dye competition experiment,indicating that Paeonia suffruticosa Andr.flower buds infiltrated into cells to bind to DNA,affecting the normal function of DNA.At the same time,the increase of intracellular ROS,indicating that the cells were oxidative damage,and RT-PCR analysis showed that the transcription of S.aureus virulence gene hla,sea,tst and agrA and E.coli O157:H7 virulence gene stx2,eae and ygaG was inhibited.