Antibacterial activity of raw milk against Listeria monocytogenes

Raw bovine milk was shown to contain anti-Listeria monocytogenes activity. L. monocytogenes inoculated into raw milk at 37°C to give an initial bacterial concentration of approximately 10,000 cfu/mL multiplied at a reduced rate for approximately 12 hours and then rapidly lost viability. Fifty-six hours after the inoculation of raw milk, no viable cells of L. monocytogenes were detectable. The anti-Listeria system was most active in raw milk incubated at 37°C. The activity was reduced at lower temperatures of 25°C, 7°C and 4°C; by heating the milk at 72°C for 15 seconds (pasteurisation); and by storing the milk at 4°C for 4 to 6 days. These preliminary results require further study to elucidate the mechanism of anti-Listeria activity in raw milk and also to determine the role of antimicrobial systems in the control of pathogenic and spoilage micro-organisms in milk products.