Study On The Antibacterial Mechanism Of Phenyllactic Acid With Food-borne Pathogens

As people take more attention to the food safety,the development of new preservatives has become a hotpot in recent years.D-?+?-3-Phenyllactic acid?PLA?is a novel organic acid with strong antibacterial and antifungal activities on food spoilage microorganisms and has a good application prospect.The antibacterial mechanism of PLA with L.monocytogenes 10403s and E.coli 44752 from cell wall,cell membrane and DNA was studied and the pecific content as follows:The permeability of food spoilage bacteria cell walls treated with PLA was determined by UV-visible absorption.The results showed that the permeability of L.monocytogenes 10403s cell wall was damaged by PLA,which equal to 28%of TritonX-100,and the damagement of E.coli 44752 was equal to 1.6%.The ability of PLA to permeate the outer cytoplasmic membrane was determined by Fluorescence spectrophotometry,and the results showed that the outer membrane had been destroyed by PLA when using NPN as a fluorescence probe,the transparent rate was25%equal to TritonX-100;The inner membrane permeation of E.coli 44752 also had a great change when treated with PLA and equivalent to 53%of the TritonX-100 by ONPG inducible enzyme lactose indicator method.Using flow cytometry to determine the membrane permeation of L.monocytogenes 10403s and the results showed that when the bacteria treated with PLA?MIC?for 1 h,the permeation has been the most with90.6%.The ability of PLA to permeate the cytoplasmic membrane was determined by flow cytometry and the results showed that a gradual increase of fluorescence intensity by PI-staining with PLA over time,denoting a damage of membrane integrity of Listeria monocytogenes 10403s and E.coli 44752.The most of the cells were stained with PI due to be treated with PLA?MIC?of E.coli 44752 caused an increase in the positive with86.1%as well as 91.9%of Listeria monocytogenes 10403s.The microstructrue of L.monocytogenes 10403s and E.coli 44752 treated with PLA has been determined by scanning electron microscope?SEM?.The results showed that the cell wall was damaged with holes,broken and ciscousing in group with increasing of1 h,3 h and 6 h.It is indicated that cell morphological had been changed and cell membrane rupture macromolecular outflows increased viscosity,bacteria viscous each other and influence respiratory and metabolic function,eventually killing bacteria.To evaluate the DNA binding activity of the PLA,the electrophoretic mobility shift assay was performed.The results showed that PLA could interact with Listeria monocytogenes 10403s and E.coli 44752 genomic DNA in outside when treated with PLA for 1 h but has no effect inside cells.UV-visible absorption titration method and calculation of the binding constant had been used to monitor the interaction of genomic DNA with PLA.The results indicated that PLA could bind with DNA with the binding constant K=9.16×10⁵ M^-11 for Listeria monocytogenes 10403s and the binding constant K=7.36×10⁵M^-1for E.coli 44752.