Salmonella

From Free net encyclopedia

This page primarily focuses upon the bacteria. For the disease, see Salmonellosis

{{Taxobox | color = lightgrey | name = Salmonella sp. | image = salmonellaNIAID.jpg | image_width = 240px | regnum = Bacteria | phylum = Proteobacteria | classis = Gamma Proteobacteria | ordo = Enterobacteriales | familia = Enterobacteriaceae | genus = Salmonella | genus_authority = Lignieres 1900 | subdivision_ranks = Species | subdivision = S. bongori
S. enterica
}} Salmonella is a genus of rod-shaped Gram-negative enterobacteria that causes typhoid fever, paratyphoid fever and foodborne illness. It is motile in nature and produces hydrogen sulfide.

1 History
2 Microbiology
- 2.1 Classification
3 Salmonella Associated Diseases
4 References
5 External links

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History

Salmonella was named after Daniel Elmer Salmon, an American veterinary pathologist who, together with Theobald Smith (better known for his work on anaphylaxis), first discovered the Salmonella bacterium in 1885 from pigs. [1] [2].

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Microbiology

Salmonella are Gram negative bacteria. In a clinical laboratory, they are usually grown isolated on blood agar, CLED agar, XLD agar or DCA agar. On blood agar, they form moist colonies about 2 to 3 mm in diameter. They do not ferment lactose.

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Classification

Salmonella taxonomy is complicated. <ref>Template:Cite journal</ref> Currently (7 Dec 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 (totalling over 2000) 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 recommend that Salmonella species be referred to only by their genus and serovar:
e.g.,
Salmonella Typhi
instead of the more correct designation,
Salmonella enterica subspecies enterica serovar Typhi.

Salmonella isolates are most usually classified according to serology (Kauffman-White classification) (Salmonella subcommittee, 1900). The main division is first by the somatic O antigen, then by flagellar H antigens. H antigens are further divided into phase 1 and phase 2. The full description of a Salmonella isolate is given as (O antigens, Vi : H antigen phase 1: H antigen phase 2).

Examples:

Salmonella Enteritidis (1,9,12:g,m)

(The O antigens present are 1, 9 and 12; the H antigens are g and m)

Salmonella Typhi (9,12,Vi:d:−)

(The O antigens are 9, 12, and Vi; the H antigen is d)

In a clinical laboratory, only a small number of serovars are looked for (the remainder being rare or not clinically significant). The HPA recommend testing for the following antigens routinely:

O antigens: 2 4 6.7 8 9 and 3.10
phase 1 H antigens: 1 2 3 4 5 6 7
phase 2 H antigens: a b c d E G i r

Isolates that cannot be identified using this panel are sent to the reference laboratory for identification.

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Salmonella Associated Diseases

Disease-causing salmonellae have recently been re-classified into a single species, Salmonella enterica, which has numerous strains or serovars. Salmonella Typhi is a well known serovar that causes typhoid fever. Other salmonellae are frequent causes of foodborne illness, and can especially be caught from poultry and raw eggs and more generally from food that has been cooked or frozen, and not eaten straight away. In March 2006, The New York Times reported that the US government said that 16.3% of all chickens were contaminated with salmonella. In the mid to late 20th century, Salmonella enterica serovar Enteritidis was a common contaminant of eggs. This is much less common now with the advent of hygiene measures in egg production and the vaccination of laying hens to prevent salmonella colonisation. Many different salmonella serovars also cause severe diseases in animals other than human beings.

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References

{{cite journal

| author=Salmonella Subcommittee of Nomenclature Committee of the International Society for Microbiology
| title=The Genus Salmonella Lignières
| journal=J Hyg
| year=1900
| volume=34
| pages=333–350
}}