Antibacterial Mechanism Of Litsea Cubeba Essential Oil Against Escherichia Coli O157:H7 And Its Application In Vegetable Juice

As one kind of natural antimicrobial substance,plant essential oil has become the focus of studying due to its safety,low toxicity,broad spectrum ntibacterial activity and no drug resistance.However,undefined antibacterial mechanism of plant essential oil restricts its further application in food industry.As a result,litsea cubeba essential oil(LC-EO)was employed in this study as a natural antibacterial agent for exploring its antibacterial mechanism against Enterohemorrhagic Escherichia coli O157:H7(EHEC O157).The destructive effect on cytomembrane of bacterial cells treated by LC-EO was observed by scanning electron microscope and transmission electron microscope.Furthermore,the leakage of intracellular organic matter such as electrolyte,protein and nucleic acid was measured.On this basis,the inhibiting effects of LC-EO on physiological metabolism of EHEC O157,including respiratory metabolism,protein synthesis capacity,energy metabolism and enzyme activity,were also tested in this study.Besides,the antibacterial mechanism was further illuminated by acquiring the influence of LC-EO treatment on genes of EHEC O157.Finally,the LC-EO was added in four different vegetable juice systems and its practical antibacterial activity was evaluated.The main results are as follows:(1)The minimal inhibitory concentration(MIC)and minimal bactericidal concentration(MBC)of LC-EO against EHEC O157 was 0.5 mg/mL and 2.0 mg/mL,respectively.And 99.999% population of EHEC O157 could be inactivated under the treatment of LC-EO(MIC)for 4 h.(2)The LC-EO treatment could change EHEC O157 cell membrane surface properties and lead to the leakage of intracellular organic matter including electrolyte,protein and nucleic acid by disrupting the cell membrane.(3)The LC-EO treatment could inhibit the tricarboxylic acid cycle(TCA)and three key enzymes(?-ketoglutarate dehydrogenase,citrate synthase and isocitrate dehydrogenase mitochondrial)activity of EHEC O157.(4)The LC-EO treatment could inhibit the physiological metabolism of EHEC O157 by inhibiting energy metabolism(declining intracellular ATP content and ATPase activity),decreasing protein synthesis capacity and lowering three key enzyme(alkaline phosphatase and ?-galactosidase)activity.(5)The LC-EO treatment could inhibit DNA topoisomerase activity,decrease intracellular DNA content and inhibit transcription level of four main virulence genes(stx1,stx2,ehxA,eae)of EHEC O157.What's more,the UV absorption spectroscopy analysis indicated that the principal component of LC-EO(citral)could react with DNA in the form of chimera.(6)The LC-EO exhibited high antibacterial activity when it was applied in four different vegetable juice systems.