Activity of ε-polylysine against Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes

Abstract

ε-polylysine is a homopolymer of L-lysine, an essential amino acid, with a reportedly wide antimicrobial spectrum. This study evaluated the antimicrobial activity of ε-polylysine, as compared with known preservatives and organic acids, against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes, in culture broth. The compounds tested included ε-polylysine (0.0025% to 0.05%), sodium diacetate (0.25%), sodium lactate (3.0%), lactic acid (0.1%), and acetic acid (0.1%), alone, as well as in combination with ε-polylysine (0.0025% to 0.03%); all treatments were evaluated in tryptic soy broth supplemented with 0.6% yeast extract. Treatments were inoculated (approximately 2 log colony-forming units [CFU]/mL) with 5-strain (E. coli O157:H7, S. Typhimurium) or 10-strain (L. monocytogenes) mixtures of the pathogens. Survival/growth of the inoculated bacteria was periodically monitored during incubation at 4°C (30 d) and 24°C (48 h). Bactericidal effects of ε-polylysine were obtained against E. coli O157:H7 and S. Typhimurium at 4°C. At the same temperature (4°C), ε-polylysine alone or in combination with other compounds tested inhibited growth or was bactericidal against L. monocytogenes. All 3 pathogens were inhibited by ε-polylysine at 24°C; however, L. monocytogenes was the most sensitive and S. Typhimurium the most resistant. The antimicrobial activity of ε-polylysine against E. coli O157:H7 and S. Typhimurium was enhanced (P < 0.05) when tested in combination with sodium diacetate or acetic acid. Combination treatments with sodium lactate resulted in loss of ε-polylysine activity by the end of the incubation period. Overall, under the conditions of this study, ε-polylysine exhibited antimicrobial effects against the 3 pathogens tested. © 2005 Institute of Food Technologists.