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 develop osteomyelitis.
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: Sep 15, 2014