Any of the rod-shaped, gram-negative, non-oxygen-requiring bacteria that make up the genus Salmonella .
Their main habitat is the intestinal tract of humans and other animals. Some of the 2,200 species exist in animals without causing disease; others are serious pathogens. Any of a wide range of mild to serious infections caused by salmonellae are called salmonellosis, including typhoid and paratyphoid fever in humans. Refrigeration prevents their reproduction but does not kill them; as a result, many salmonellae can develop in foods, which, when eaten, can cause gastroenteritis . Chickens are major reservoirs of salmonella, and chicken and eggs are the principal source of human poisoning, whose symptoms include diarrhea, vomiting, chills, and painful headaches. Other food sources include unpasteurized milk, ground meat, and fish.