Review. Dairy farm management and production practices associated with the presence of Listeria monocytogenes in raw milk and beef

Abstract

Human listeriosis is a severe foodborne disease caused by Listeria monocytogenes. It is a zoonosis that represents a significant concern for the food industry due to the high mortality rate it causes and the fact that the organism is capable of growing at refrigeration temperatures. Dairy products and ready-to-eat meats are among the foods most often involved in listeriosis outbreaks. Listeria is a common contaminant in the dairy environment, both on the farm and in the processing plant. The main sources of L. monocytogenes in dairy farms are manure and improperly fermented silage. If silage crops are grown on contaminated land, a new cycle of silage contamination and faecal shedding by ruminants that consume such silage may ensue. High loads of L. monocytogenes produced in farm environments may thus represent a primary source for the introduction of this pathogen into the human food supply chain; dairy cows would represent a reservoir for the bacterium, and raw milk and beef would represent the main vehicles for its transmission from dairy farms to humans. Even if contamination originates in post-processing environments, contaminated raw foods may still represent a vehicle for introducing L. monocytogenes into food processing plants.Molecular typing methods have confirmed that common strains of L. monocytogenes are present in dairy farm-associated isolates and isolates from both human epidemic and sporadic cases. Pre-harvest (on-farm) control of listeriosis should be basedmainlyon the control of manure, silage, herd health and milking practices.