Antibacterial Activity And Mechanism Of Action Of Phenyllactic Acid

The diseases caused by food borne pathogens have become a social public security problem among many countries in the world.With the development of social economy,the public give food quality and nutrition of high expectations.In view of this,many governments,enterprises and scientific researchers attach great importance to develop pollution-free,good effect and affordable food additives.3-Phenyllactic acid(PLA)is a kind of high-value organic acid and a new natural broad-spectrum antimicrobial agent,it can be produced by lactic acid bacteria and other microbial metabolism.For most of the gram-positive,gram-negative bacteria and fungi,phenyllactic acid has significant antibacterial effect.Therefore,the two kinds of enantiomer L-phenyllactic acid and D-phenyllactic acid of phenyllactic acid were selected as raw materials to study their antibacterial properties and antibacterial mechanism.The main contents and results of the research are as follows:(1)The two enantiomers of PLA: L-PLA and D-PLA are selected to study their antibacterial performance.We found that both of L-PLA and D-PLA have strong bacteriostatic effect on eight pathogenic bacteria tested,such as Staphylococcus aureus and Escherichia coli.The results of MIC and MBC indicated that the antibacterial ability of D-PLA is slightly better than that of L-PLA.Growth curve results show that the higher the concentration of L-PLA,the more significantly inhibitory of bacteria,even low concentration of L-PLA could delay the arrival of logarithmic phase in bacterial growth.(2)Intensively study the inhibiting mechanism of L-PLA on the two indicator bacteria:Bacillus subtilis and Pseudomonas aeruginosa.Through cell integrity test,scanning electron microscope(SEM),transmission electron microscopy(TEM)and fluorescence inverted microscope observation experiment,we analyzed the effect of L-PLA on bacterial membrane system.These experimental results show that L-PLA play an inhibitory role in cell wall and cell membrane structure,caused the destruction of cytoskeleton,cell depression and fracture,leading to the loss of intracellular material.SDS-PAGE gel electrophoresis and agarose gel electrophoresis experiment results further show that after the structure of cell membrane system destroyed,L-PLA entered into the cell,not only can it inhibit normal protein and DNAsynthesis,but also be combined with DNA,which suppresses the normal growth of bacteria.Flow cytometry instrument was used to detect bacterial cell survival and apoptosis.The results reflect that L-PLA causes bacterial cell apoptosis rapidly and results in cell death ultimately.All in all,the results revealed that bacterial growth inhibiting effect of L-PLA occurs in the two aspects of cell and molecular level.