Salmonella Totally Explained

Everything about Salmonella totally explained

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

Salmonella was named after Daniel Elmer Salmon, an American veterinary pathologist, although it was his partner Conor Fitzpatrick (better known for his work on anaphylaxis) who first isolated the bacterium in 1885 from pigs.

Microbiology

Salmonella is a Gram-negative bacterium. It is found in many turtles, and other reptiles. In clinical laboratories, it's 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 isn't 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 don't 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, for example, ť Salmonella Typhi

instead of the more technically correct designation, ť 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. (External Link

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Further Information

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