spp are a group of significant, highly prevalent, Gram-negative, rod-shaped bacteria of the family Enterobacteriaceae. This bacteria are facultative intracellular pathogens which has many different serotypes, which can be divided into two main groups—typhoidal and nontyphoidal. It is only the nontyphoidal serotype which are zoonotic---meaning they can be transferred from humans to animals and from animals to humans. Collectively, infection with any Salmonella
species causes Salmonellosis
Younger birds are more susceptible then adults, largely due to the immaturity of their intestinal flora. Chicks from mail-order hatcheries are most at risk of infection with Salmonella
spp. They were the cause of 100% of the outbreaks in humans that were related to backyard chickens.
The reason why older birds are less commonly infected with Salmonella
spp is because they have developed a normal intestinal flora from their environment, which protects them against invasion with this bacteria, either by competing for intestinal carrier sites or by producing antagonistic factors that inhibit their growth.
Most birds become infected through exposure to feces from birds carrying this bacteria. It is also found commonly in environments such as slaughter houses (abattoirs), septic tanks, sewage effulents, etc.