Interactive inhibition of meat spoilage and pathogenic bacteria by lysozyme, nisin and EDTA in the presence of nitrite and sodium chloride at 24 °C

To develop a nisin- and lysozyme-based antimicrobial treatment for use with processed ham and bologna, in vitro experiments were conducted to determine whether inhibition enhancing interactions occur between the antimicrobials lysozyme, chrisin (a commercial nisin preparation), EDTA, NaCl and NaNO2. Inhibitory interactions were observed between a number of agents when used against specific pathogenic and spoilage bacteria. The observed interactions included lysozyme with EDTA (Enterococcus faecalis and Weissella viridescens), chrisin with EDTA (all Gram-positive organisms), EDTA with NaCl (Escherichia coli, Salmonella enterica serovar Typhimurium, Serratia grimesii), EDTA with nitrite (E. coli, Lactobacillus curvatus, Leuconostoc mesenteroides, Listeria monocytogenes, S. Typhimurium), chrisin with nitrite (Lc. mesenteroides, L. monocytogenes), and NaCl with nitrite (S. Typhimurium, Shewanella putrefaciens). Previous reports have described interactions between nisin with EDTA that resulted in enhanced antimicrobial effect against Gram-negative bacteria, or lysozyme with nisin against Gram-positive bacteria. These interactions were not observed in these experiments. We observed that unlike previous studies, these experiments were conducted on growing cells in nutrient broth, rather than under conditions of nutrient limitation. We propose that screening of antimicrobials for use in food systems in nutrient-deficient systems is inappropriate and that new protocols should be developed.