Broad-Spectrum Antimicrobial Activity of a Natural Peptide, e-Poly-L-lysine
1Kazuya Yamanaka, 2Hirotaka Furukawa*, 1Jun Hiraki and 1 Masamichi Muto
1Chisso Corporation Yokohama Research Center, Yokohama, Japan
2Chisso America Incorporated, Hayward, California
e-Poly-L-lysine (e-PL), produced by Streptomyces albulus, is a naturally occurring homo polymer (25-35 mer) characterized by a peptide linkage between the carboxyl and e-amino groups of L-lysine. Since e-PL, being positively charged due to the amino groups, shows antimicrobial activity, much attention has focused on its potential as a natural food preservative. Although numerous biological and toxicological studies of e-PL have been reported, its antimicrobial properties are surprisingly poorly understood. Given the potential importance of the characterization of e-PL as a food preservative, we investigated its basic properties. The minimal inhibitory concentration (MIC) and the minimal bactericidal concentration (MBC) of e-PL against a number of microorganisms were evaluated. Unlike most commonly used antimicrobial compounds, the MBC values, measured under low-concentration buffer conditions, were lower than the MIC values. Bactericidal kinetics against some microorganisms was measured in the presence and absence of culture media. It was confirmed that culture media inhibited the antimicrobial activity of e-PL. When the antimicrobial activity found for e-PL was compared with those for a number of antimicrobial compounds in commercial use, it was shown to have high antimicrobial potential, notably against Listeria monocytogenes.