Antibacterial activity of raw milk against Listeria monocytogenes

Raw bovine milk was shown to contain anti-Listeria monocytogenesactivity. L. monocytogenes inoculated into raw milkat 37°C to give an initial bacterial concentration of approximately10,000 cfu/mL multiplied at a reduced rate forapproximately 12 hours and then rapidly lost viability. Fifty-sixhours after the inoculation of raw milk, no viable cells ofL. monocytogenes were detectable. The anti-Listeria systemwas most active in raw milk incubated at 37°C. The activitywas reduced at lower temperatures of 25°C, 7°C and 4°C; byheating the milk at 72°C for 15 seconds (pasteurisation); andby storing the milk at 4°C for 4 to 6 days. These preliminaryresults require further study to elucidate the mechanism ofanti-Listeria activity in raw milk and also to determine the roleof antimicrobial systems in the control of pathogenic andspoilage micro-organisms in milk products.