Genus of Gram negative, facultatively anaerobic rod-shaped bacteria of the family Enterobacteriaceae. Occur in soil, water, foods (e.g. raw meat, raw sea foods, eggs and dairy products) and the gastrointestinal tract of humans and animals (especially poultry and swine). Salmonella Ty-phi is the causative agent of typhoid fever, while Salmonella Typhimurium and Salmonella Enteritidis are responsible for gastroenteritis. Transmission is via the faecal-oral route by contaminated foods or water.