Growth of Listeria monocytogenes in naturally-contaminated raw milk.

Milk from a cow shedding L. monocytogenes was collected and stored at various temperatures. Average generation times of 25.3, 10.8 and 7.4 h were observed at storage temperatures of 4, 10 and 15°C, respectively. The affected cow appeared to be heavily infected in only one of the four quarters of the udder. Shedding of L. monocytogenes has continued for nearly 3 years now, with the milk appearing normal. Carrier animals that do not develop a full blown mastitis and are continuous shedders of L. monocytogenes are an obvious public health problem