Antimicrobial Effect And Mode Of Action Of Eugenol On Staphylococcus Aurens

Eugenol is a food additive with widely antibacterial effect which is extracted from plants.In order to find out the antibacterial effect and the mode of action of Eugenol on S.aurens at the molecular level,the inhibitory effect,such as the minimum inhibitory concentration and the minimum bactericidal concentration,the changes of the physiological indicators,the bacterial morphology structure and transcript expression were studied preliminaryly.The results are as follows:The minimum inhibitory concentration?MIC?and the minimum bactericidal concentration?MBC?were tested by three methods,the constant dilution method,the microdilution method and plate dilution method.And the results showed that Eugenol had inhibitory effect on S.aureus with concentration dependment.The MIC was 600?g mL^-1,and the MBC was 700?g mL^-1.The change on bacterial morphology was observed by scanning electron microscopy?SEM?and transmission electron microscope?TEM?.After affected by eugenol,the morphology has changed,the cells structure was disordered,a large amount of material extravasation and the cell deformities.Hence,resulting in cell death.The activity of the malate dehydrogenase?MDH?and the succinate dehydrogenase?SDH?were studied by spectrophotometer method to explore its effect on physiological metabolism.And the results showed that the eugenol significantly reduces the activity of MDH and SDH of S.aureus?P<0.05?,and increase the cell membrane permeability.And the higher the concentration,the lower the MDH activity and the SDH activity.Meanwhile,the membrane potential of S.aureus with the treatment of eugenol was studied by monitoring for the cell membrane permeability.The results showed that the fluorescence intensity?FL?of S.aureus was enhanced,indicating that the membrane potential of the cell membrane was polarized.The cell membrane potential remained depolarized with the increase of processing time and concentration.And with the cell activity decreasing,the degree of the depolarization is decreasing,too.The effect of eugenol on transcription expression of S.aureus was investigated by the high-throughput technology,RNA-seq.And then we found eugenol impacts the S.aurens through multiple targets on it's growth and development,such as peptidoglycan,teichoic acid,cellmembranes,DNA damage repair and and metabolic pathways.Therefore,we guess the mechanisms were that:?1?changing the integrity and permeability of cell membrane and cell wall,and destroying the structure of bacterial cells;?2?inhibiting the enzymatic reaction of energy metabolism and interfering with energy metabolism and material metabolism pathway;?3?obstructing the DNA damage response pathway of bacterial genetic material,and destroying the integrity of genetic information;?4?reducing the adaptability of S.aureus to the environment,resulting in the disorder and lysis.