Research On The Bacteriost Mechanism And Influence-factor Of ?-poly-L-lysine On Escherichia Coli

?-Poly-L-lysine(s-PL)is a kind of cationic antimicrobial peptide that consists of 25-30 residues of L-lysine.?-PL has been approved by multiple countries as a preservative in food because of its safety,strong antimicrobial activity and other excellent properties.Although the s-PL has many proven advantages,its specific antimicrobial mechanism is not clear.Moreover,the interaction between ?-PL and anionic polysaccharides may produce a certain impact on liquid food systems.Therefore,in this study,the effect of ?-PL on the antibacterial activity of E.coli and influence factors were investigated.s-PL concentrations ranging in this experimental study was determined by measuring dose-response curve,survival rate and biomass of E.coli under different concentrations of s-PL action.And it found that the bacteriostatic activity of ?-PL on E.coli become remarkable with the concentration increasing and showed concentration-dependent.The effect of ?-PL on the membrane integrity of cell surface was also investigated.The experimental results showed that the inner and outer membrane of E.coli treated by?-PL was damaged,cell membrane permeability was increased and its integrity was significantly disrupted.The above phenomenon becomes apparent with the increase of concentration of ?-PL.When the concentration of ?-PLwas increased to 50 ?g/mL,a hump and depressing surface of E.coli cells were clearly observed by scanning electron microscopy(SEM).Bacteria gathered to form cell mass.When treated with 100 pg/mL and 150 ?g/mL ?-PL,cell surface become severely rough,shrinking and sunk,and a great deal of irregular substance appeared around cell mass with the increasing ?-PL concentration.Grain-size instrument detection found that intercellular adhesion phenomenon became serious with the increasing ?-PL conceration,and cenobium formed bigger.When treated with ?-PL,green fluorescence of E · coli cells were clearly observed by fluorescence microscope.According to experimental guess,we measured the polysaccharides content in E.coli broth after the action of ?-PL.The results indicated that polysaccharide content in E.coli broth increased with the growing s-PL concentration,and LB medium also contained polysaccharide.Meanwhile,?-PL intereacted with peptone and formed a kind of turbid substance during the experiment.According to appearance observation,turbidity,bacteriostatic activity as an index to investigate the effect of LB culture medium on bacteriostatic activity of s-PL.The results show that:(1)The turbidity of liquid mixture and diameter of inhibition zone increase with its concentration increased when other conditions unchanged;(2)The diameter of inhibition zone was weaken with peptone concentration increased by controlling other conditions unchanged;(3)The turbidity of liquid mixture was gradually weakened and diameter of inhibition zone was weakened and strengthened with the increasing of salt ion concentration when the other conditions unchanged;(4)The turbidity of liquid mixture was strengthened and then weakened and diameter of inhibition zone was weakened and then strengthened with the increasing of pH when the other conditions unchanged.we can speculate that peptone,pH,ionic strength will have a certain impact on the antibacterial activity of ?-PL.In conclusion,?-PL inhibited E.coli through attaching to the cell surface,and disrupting the structures of cell wall and membrane.Moreover,bacteriostatic activity of?-PL be affected by anionic trash,pH and salt ion concentration.