The Action Mechanism On Staphylococcus Aureus And Application Of Antimicrobial Peptide Produced By Lactobacillus Paracasei FX-6

Antimicrobial peptides have different from the antibacterial mechanism of traditional antimicrobial drugs, and potential for use as safe and effective new antimicrobial and new preservative.This paper focuses on the preparation, qualitative andquantitative analysis, mechanism on Staphylococcus aureus of antibacterial peptide F1 which was isolated from Lactobacillus paracasei FX-6 fermented milk before, meanwhile,the application assessmentof FX-6 fermented extracts was also studied. The main research contents and results were as follows:(1) The antibacterial spectrum of FX-6 fermented extracts were studied using Staphylpcoccus aureus,Escherichia coli,Shigella dysenteriae,et al.The results showed that FX-6 fermented extracts had broad-spectrum antibacterial antibacterial activity. Moreover,FX-6 fermented extracts has security and stable antibacterial activity in the common physical and chemical environment.Antibacterial peptide F1 has significant inhibitions on S.aureus,the minimum inhibitory concentration was 59.13±0.20 ?mol/L, minimum bactericidal concentration was 175.04±2.46 ?mol/L. Moreover, antibacterial peptide F1 has security.(2) Effect of F1 on cell surface characteristics and DNA of S.aureus. The electrostatic attraction and hydrophobic interaction play a major role in the binding process of F1 with S.aureus.F1 could expose the hydrophobic region of the membrance of S.aureus, increase the cell membrane permeability and damage the membrane integrity of S.aureus, leading to the overflow of the intracellular contents.F1 penetrated into cell and bond to DNA, leading to the bacterial cell cycle changed.(3) The gene and protein expression and metabolic pathways of the effect of F1 onS.aureus were investigated basing on the technology of RNA-seq transcriptomics and i TRAQ quantitative proteomics.Substantial changes in the expression levels of 159 proteins and 719 genes were detected.Among these, the expression of 91 proteins and 430 genes showed decreased. The increased expression of D-alanine-poly(phosphoribitol) ligase subunit 1 and dlt A gene might affected the peptidoglycan synthesis, and then the cell wall became thinner. Pot A protein and pot A gene were significantly up-regulated, it might affected the spermidine/putrescine ABC transporter system and the growth and reproduction of S.aureus. The expression levels of H1T5G6 protein,asd gene,H4BH02 protein,dap A gene dropped down,it inhibited and interdicted the lysine biosynthesis pathway,leading to increased binding of antimicrobial peptide F1 by the S.aureus and inhibited the peptidoglycan biosynthesis.The decreased expression of Scd A protein and scd A gene led the abnormality of the cell cycle and cell morphology.(4) The preservative application assessment of FX-6 fermented extracts.The preservative effects of distilled water, 0.5% FX-6 fermented extracts, 0.5% potassium sorbate and 0.5% nisin on shrimp were investigated respectively during storage at 4?.The results showed that the 0.5% FX-6 fermented extracts had better fresh-keeping effects on shrimp than 0.5% potassium sorbate and 0.5% Nisin, it could extend the shelf life of shrimp to 8 d. Moreover, FX-6 fermented extracts could improve storability of litchi and longan fruits. In addition, FX-6 fermented extracts and Sportak compounds had synergy effect making preservative effect stronger than single preservative. The compounds treatments could significantly preserved litchi fruits, and health fruit rate was 71.43%.