Salmonella are gram-negative bacteria and are responsible for 1 out of 4 key global cases of diarrheal disease. Foodborne diseases are a substantial burden on human health as they affect 1 in 10 people throughout the world every year, and they are fatal for 33 million of them. Poultry food production is the production sector of most concern as far as foodborne illness through meat and eggs is concerned.

About 2400 types of Salmonella, called serovars, have been identified. Some of the most frequently encountered are S. Heidelberg, S. Enteritidis, S. Indiana, S. Kottbus, S. Infantis, S. Montevideo, S. Saintpaul, S. Senftenberg and S. Typhimurium. Salmonella is a zoonosis, which means that an animal can transfer the disease to humans.

The control of Salmonella in a farm environment is key to preventing contamination and infection. Salmonella colonizes the gut in three steps. First by adhesion, then by invasion of the epithelium, and finally by infecting the lymphoid tissues. Salmonella impairs the homeostasis of the gut (according to the three pillars: microbiota, mucosal barrier, inflammation state) and uses the host defense mechanisms to its advantage. Indeed, the inflammation induced by Salmonella leads to the inhibition of commensal micro-organism growth in the gut. Moreover, when an animal suffers from stress, “blood” enters the gut and brings oxygen with it. Salmonella is facultative anaerobic, while commensal bacteria are often more anaerobic, thus offering Salmonella the possibility of multiplying very quickly. This allows Salmonella to take advantage of other commensal bacteria, multiply and colonize the host gut.

The animals generally have no symptoms, which makes the diagnosis complicated and increases the risk of sending contaminated carcasses to the slaughterhouse. Regulations are in force in some countries, but not in others. In the case of regulation, the Salmonella status of the flock can be checked by organizing environmental and fecal swabs on the farm to obtain the status of the flock before they are sent to the slaughterhouse. If the flock is positive, its value decreases, and it becomes a burden for the slaughterhouse.