Antimicrobial Activity of ɛ‐Polylysine against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in Various Food Extracts

Abstract

This study compared the antimicrobial effects of epsilon-polylysine (epsilon-PL) against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in 6 food extracts and in broth. The food extracts (10% (w/w) in distilled water) evaluated were fat-free and whole fat milk, beef, bologna, rice, and vegetables (50:50 ratio of broccoli and cauliflower). epsilon-PL was tested at 0.005% and 0.02% (w/v) against E. coli O157:H7 and L. monocytogenes, and 0.02% and 0.04% (w/v) against S. Typhimurium. The substrates were inoculated (5 log CFU/mL) and periodically analyzed for surviving populations during storage at 12 degrees C for 6 d. In general, all 3 pathogens reached 7 to 9 log CFU/mL within 2 d in control substrates (no epsilon-PL). Immediate bactericidal effects (P < 0.05) following exposure to epsilon-PL were obtained in the rice (all pathogens) and vegetable (E. coli O157:H7 and S. Typhimurium) extracts. During storage, antimicrobial effects of epsilon-PL were more pronounced in the food extracts than in the broth medium. The greatest antimicrobial activity for all 3 pathogens was obtained in the rice and vegetable extracts, where counts were reduced (P < 0.05) to below the detection limit (0.0 log CFU/mL) by one or both epsilon-PL concentrations tested. In the other food extracts (fat-free milk, whole fat milk, beef, and bologna), both epsilon-PL concentrations tested generally resulted in lower (P < 0.05) pathogen levels at the end of storage compared to initial counts, with better bactericidal effects exerted by the higher of the 2 epsilon-PL concentrations. Additional research is needed to explore the potential antimicrobial effects of epsilon-PL in real food systems.