Effect Of ε-Poly-L-Lysineon Theactivity And Primary Metabolism Of Staphylococcus Aureus

ε-Poly-L-Lysine (ε-PL) is a naturally produced, cationic amino-acid homopolymer. Because of its excellent properties, ε-PL has been widely used in the food and pharmaceutical industries. ε-PL has attracted a great deal of attention as a natural food preservative. However, its antimicrobial mechanism has not been fully understood. ε-PL exhibits antimicrobial activity against a spectrum of microorganisms including Gram-positive, Gram-negative bacteria and yeasts. Of the numbers of studies elucidating the antimicrobial mechanisms of ε-PL, little investigated that on Gram-positive bacteria. In this study, the effect ofε-PL on the activity and primary metabolism of Staphylococcus aureus, was investigated.The antimicrobial activity of ε-PL against S. aureus was studied and showed concentration-dependent. The effect of ε-PL on the characteristic and morphology of cell surface was also investigated. A decrease in cell surface hydrophobicity was induced by ε-PL. After treating with ε-PL, cell membrane permeability was increased and its integrity was significantly disrupted. The Raman spectroscopy indicated a structural change in peptidoglycan, which was the major component of cell wall. When treated with 250 μg/mL ε-PL, a rough and depressing surface of S. aureus cells were clearly observed by scanning electron microscopy (SEM). At the concentration of 500 μg/mL and 750μg/mL, ε-PL induced collapse of S. aureus cells.The metabolomics analysis of changes in intracellular metabolites in ε-PL treated S. aureus cells was based on GC/MS. The results of multivariate statistical analysis revealed the differences among groups in the intracellular metabolite. The analysis of concentration changes in intracellular metabolites indicated that the utilization of glucose was inhibited in ε-PL treated cells, inducing decreases in the concentration of glycerate-2P and glycerate-3P, key intermediate metabolites in glycolysis. It was found that the contents of succinate and fumarate involved in TCA cycle were reduced. The above results implied that ε-PL imposed restrictions on primary metabolic pathways by inhibiting tricarboxylic acid cycle and glycolysis.It was found that the contents of certain amino acids, e.g. proline and alanine, increased after treating with ε-PL, while decreased as the concentration of ε-PL increased. These amino acids were indicated to be involved in the limited stress resistance of S. aureus. To verify the results of metabolomics analysis, the activities of key enzymes involved in glycolysis and TCA cycle, as well as the level of intracellular ATP were assayed. The activities of hexokinase, succinode hydrogenase and aconitase declined in ε-PL treated cells, and the ATP level showed similar trend.In conclusion, s-PL inhibited S. aureus through attaching to the cell surface, and disrupting the structures of cell wall and membrane, inducing interruption of intracellular metabolites.