Antimicrobial Activity And Mechanism Of Olive Polyphenols Against Food-borne Pathogens

Natural plant extracts which have rich polyphenols are considered to have an effective antimicrobial activity on food-borne pathogens.Olive is a plant with rich polyphenols.In recent years,most studies focused on antimicrobial activity of olive oil and olive leaf extracts on food-borne pathogens.There are few studies on the antibacterial effect of olive polyphenols on food-borne pathogens.The antibacterial mechanism still needs investigation.Therefore,this study was conducted to analyze the antibacterial activity of olive polyphenols against several food-borne pathogens and reveal the antibacterial mechanism.Salmonella typhimurium ATCC 14028,Staphylococcus aureus ATCC13565 and Listeria monocytogenes CMCC54004 were selected as research object.The antibacterial effect was assessed by value of minimum inhibitory concentration(MIC)and survival populations of strains with treatments of olive polyphenols of different concentrations.The changes in cell membrane potential,intracellular ATP concentration,cell morphology,and the effect of bacterial protein were analyzed to reveal possible mechanism of action.The results were as follows:The MIC of olive polyphenols against Salmonella typhimurium,Staphylococcus aureus,and Listeria monocytogeneswere 0.6250 mg/mL,1.2500 mg/mL and 1.2500 mg/mL.With the increase of the concentration of olive polyphenols,the antibacterial activity of three food-borne pathogens gradually increased.The effect of olive polyphenols on the bacterial cell membrane was studied by measuring the changes of bacterial cell membrane potential.The results showed that the bacterial cell membrane was depolarized,which caused damage to the bacterial cell membrane.The effect of olive polyphenols on bacterial energy was studied by measuring changes in ATP content of cells.Our results indicated that compared with unstressed cell,intracellular ATP levels of three food-borne pathogens cells treated with olive polyphenols significantly dropped(P < 0.01).The effect of olive polyphenols on cell morphology was observed by transmission electron microscopy(TEM).Obvious losses of cell integrity were found in the cells treated with olive polyphenols,including irregular wrinkles,rough surface,separation of the cytoplasmic membrane from cell wall,deformation and collapse of cell,and leakage of cytoplasmic content.In our study,the content of soluble proteins in supernatant of three food-borne pathogens cell treated with olive polyphenols is obviously reduced.Following treatment with olive polyphenols for 12 h,most of the protein bands of three food-borne pathogens were disappeared,while the bands in the control group without the treatment of olive polyphenols were clear.This suggested that olive polyphenols might inhibit the synthesis of bacterial proteins of three kinds of food-borne pathogens.In conclusion,the data of this study indicated that olive polyphenols has effective antibacterial activity against Salmonella typhimurium,Staphylococcus aureus,and Listeria monocytogenes.The antimicrobial mechanism of olive polyphenols against three kinds of food-borne pathogens was elucidated,including reduction of intracellular ATP concentrations,depolarization of cell membranes,destruction of morphology,and decrease bacterial protein content.Our finding suggests that olive polyphenols could be used as the natural antibiotic and preservative to reduce the risk of foodborne pathogenic microorganisms.