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 (H₂O,) 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.