salmonella n : rod-shaped gram-negative enterobacteria; cause typhoid fever and food poisoning; can be used as a bioweapon [also: salmonellae (pl)]

English

Noun

1. Any of several rod-shaped bacteria, of the genus Salmonella, that cause food poisoning and other diseases

   The mayonnaise left in the sun at the picnic caused everyone there to come down with salmonella poisoning.

Salmonella is a genus of rod-shaped Gram-negative enterobacteria that causes typhoid fever, paratyphoid fever, and foodborne illness. Salmonella species are motile and produce hydrogen sulfide. Salmonella antibodies were first found in Malawi children in research published in 2008. The Malawian researchers have identified an antibody that protects children against bacterial infections of the blood caused by Salmonella. A study of 352 children at Blantyre's Queen Elizabeth hospital found that children up to two years old develop antibodies that aid in killing the bacteria. The researchers, quoted in the Science and Development Network, say this could lead to a possible Salmonella vaccine.

History

The genus Salmonella was named after Daniel Elmer Salmon, an American veterinary pathologist who, along with Theobald Smith, discovered the organism that causes hog cholera, Salmonella enterica var. Choleraesius.

Microbiology

Salmonella is a Gram-negative bacterium. It is found in many turtles, and other reptiles. In clinical laboratories, it is usually isolated on MacConkey agar, XLD agar, XLT agar, DCA agar, or Önöz agar. Because they cause intestinal infections and are greatly outnumbered by the bacteria normally found in the healthy bowel, primary isolation requires the use of a selective medium, so use of a relatively non-selective medium such as CLED agar is not often practiced. Numbers of salmonella may be so low in clinical samples that stools are routinely also subjected to "enrichment culture", where a small volume of stool is incubated in a selective broth medium, such as selenite broth or Rappaport Vassiliadis soya peptone broth, overnight. These media are inhibitory to the growth of the microbes normally found in the healthy human bowel, while allowing salmonellae to become enriched in numbers. Salmonellae may then be recovered by inoculating the enrichment broth on one or more of the primary selective media. On blood agar, they form moist colonies about 2 to 3 mm in diameter. When the cells are grown for a prolonged time at a range of 25—28°C, some strains produce a biofilm, which is a matrix of complex carbohydrates, cellulose and proteins. The ability to produce biofilm (a.k.a. "rugose", "lacy", or "wrinkled") can be an indicator of dimorphism, which is the ability of a single genome to produce multiple phenotypes in response to environmental conditions. Salmonellae usually do not ferment lactose; most of them produce hydrogen sulfide which, in media containing ferric ammonium citrate, reacts to form a black spot in the centre of the creamy colonies.

Classification

Salmonella taxonomy is complicated. As of December 7, 2005, there are two species within the genus: S. bongori (previously subspecies V) and S. enterica (formerly called S. choleraesuis), which is divided into six subspecies:

• I—enterica
• II—salamae
• IIIa—arizonae
• IIIb—diarizonae
• IV—houtenae
• V—obsolete (now designated S. bongori)
• VI—indica

There are also numerous (over 2500) serovars within both species, which are found in a disparate variety of environments and which are associated with many different diseases. The vast majority of human isolates (>99.5%) are subspecies S. enterica. For the sake of simplicity, the CDC recommends that Salmonella species be referred to only by their genus and serovar, e.g.,

Salmonella Typhi

instead of the more technically correct designation,

Salmonella enterica subspecies enterica serovar Typhi.

Salmonella isolates are most commonly classified according to serology (Kauffman-White classification).

Salmonellosis can also be caught by handling reptiles such as iguanas or turtles. A CDC study also noted cases of salmonellosis in 2003 and 2004 associated with handling commercially distributed pet rodents. http://www.cdc.gov/mmwR/preview/mmwrhtml/mm5417a3.htm

See also

• 1984 Rajneeshee bioterror attack
• List of foodborne illness outbreaks
• Food Testing Strips

References

External links

• Background on Salmonella from the Food Safety and Inspection Service of the United States Department of Agriculture
• Salmonella as an emerging pathogen from IFAS
• Notes on Salmonella nomenclature
• Genome information is available at the NIAID Enteropathogen Resource Integration Center (ERIC)
• Salmonella motility video
• Avian Salmonella