Antibacterial Activity of the Lactoperoxidase System Against Listeria monocytogenes and Staphylococcus aureus in Milk

The lactoperoxidase system (LPS) was activated by addition of thiocyanate (SCN-) and hydrogen peroxide (H2O2) and utilizing the inherent milk lactoperoxidase (LP). For Listeria monocytogenes studies, initial concentrations of 2.4 mM SCN- and 0.6 mM H2O2 were added. The corresponding concentrations were 1.2 mM SCN- and 0.3 mM H2O2 for Staphylococcus aureus studies. The LPS increased the predicted time to reach half the maximum attainable CFU/ml by 326 h for L. monocytogenes at 10°C and by 6.3 h at 35°C. For S. aureus , the corresponding increases were 36 h at 10°C and 2.4 h at 37°C. During the initial period after activation of the LPS, bactericidal effects against L. monocytogenes at 35°C and S. aureus at 37°C were observed. After recovery from the effects of the LPS, growth rate of each pathogen was of similar magnitude as in the H2O2-treated and untreated milk, with the exception of L. monocytogenes at 10°C.