The genus Salmonella is divided into 2 species, S. enterica and S. bongori, which include > 2400 known serotypes. Some of these serotypes are named. In such cases, common usage sometimes shortens the scientific name to include only the genus and serotype; for example, S. enterica, subspecies enterica, serotype Typhi is shortened to Salmonella Typhi.
Salmonella may also be divided into 3 groups based on how well the organism is adapted to human hosts:
Those highly adapted to humans and having no nonhuman hosts: This group includes S. Typhi and S. Paratyphi types A, B (also called S. Schottmülleri), and C (also called S. Hirschfeldii), which are pathogenic only in humans and commonly cause enteric (typhoid) fever.
Those adapted to nonhuman hosts or causing disease almost exclusively in animals. Some strains within this group—S. Dublin (cattle), S. Arizonae (reptiles), and S. Choleraesuis (swine)—also cause disease in humans.
Those with a broad host range: This group includes > 2000 serotypes (eg, S. Enteritidis, S. Typhimurium) that cause salmonella gastroenteritis and account for 85% of all Salmonella infections in the US.