A genus of rod-shaped Gram-negative bacteria that inhabit the intestine and cause disease (salmonellosis) in humans and animals. They are aerobic or facultatively anaerobic, and most are motile. Salmonellae can exist for long periods outside their host, and may be found, for example, in sewage and surface water. Humans may become infected by consuming contaminated water or food, especially animal products, such as eggs, meat, and milk, or vegetables that have been fertilized with contaminated manure. The bacteria can also be transmitted from human or animal carriers by unhygienic food preparation. The genus is divided into two species, S. bongori and S. enterica; the latter can be divided into six subspecies, each of which has various serotypes—there are over 2500 Salmonella serotypes. For example, the serotypes Enteritidis and Typhimurium of S. enterica cause gastroenteritis, whereas the serotypes Typhi and Paratyphi cause typhoid fever and paratyphoid fever, respectively.