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 are chemoorganotrophs, obtaining 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. Most isolates exist in two phases; phase I is the motile phase and phase II the nonmotile phase. Cultures that are nonmotile upon primary culture may be switched to the motile phase using a Cragie tube.
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 properly pronounced voicing the initial letter "l," since it is named for pathologist D.E. Salmon, and has nothing to do with the salmon fish.
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.
Enteritis Salmonella (e.g., ''Salmonella enterica
subsp. enterica'' serovar Enteritidis) can cause diarrhea, which
usually does not require antibiotic treatment. However, people at risk
such as infants, small children, the elderly, Salmonella can become
very serious, leading to complications. If this is not treated, HIV
patients and those with suppressed immunity can become seriously ill.
Children with sickle cell anemia who are infected with salmonella may
In Germany, Salmonella infections must be reported (§ 6
and § 7 of the German law on infectious disease prevention,
''Infektionsschutzgesetz''). Between 1990 and 2005, the number of
officially recorded cases decreased from approximately 200,000 cases to
approximately 50,000. It is estimated that every fifth person in
Germany is a carrier of Salmonella. In the USA, there are
approximately 40,000 cases of Salmonella infection reported each
year. According to the World Health Organization, over 16 million
people worldwide are infected with typhoid fever each year, with
500,000 to 600,000 of these cases proving to be fatal.
Salmonella can survive for weeks outside a living body.
They have been found in dried excrement after over 2.5 years. Salmonella is not destroyed by freezing. Ultraviolet radiation and
heat accelerate their demise; they perish after being heated to for one
hour, or to for half an hour. To protect against Salmonella
infection, it is recommended that food be heated for at least ten
minutes at so that the center of the food reaches this temperature.
About 142,000 Americans are infected each year with Salmonella enteritidis
from chicken eggs, and about 30 die. The shell of the egg may be
contaminated by feces or environment, or its interior (yolk) may be
contaminated ''in utero''.
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Last Updated: Feb 1, 2011