Salmonella are closely related to the Escherichia genus and are found worldwide in warm- and cold-blooded animals, in humans, and in nonliving habitats. They cause illnesses in humans and many animals, such as typhoid fever, paratyphoid fever, and the foodborne illness salmonellosis.
Salmonella is a genus of rod-shaped, Gram-negative, non-spore forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which project in all directions (i.e. peritrichous). They obtain their energy from oxidation and reduction reactions using organic sources and are facultative anaerobes; most species produce hydrogen sulfide, which can readily be detected by growing them on media containing ferrous sulfate, such as TSI.
Salmonella infections are zoonotic; they can be transmitted by humans to animals and vice versa. Infection via food is also possible. A distinction is made between enteritis salmonella and typhoid/paratyphoid/salmonella, whereby the latter because of a special virulence factor and a capsule protein (virulence antigen) can cause serious illness, such as Salmonella enterica subsp. enterica Serovar Typhi, or Salmonella typhi). Salmonella typhi is adapted to humans and does not occur in animals.