Shigella

Taxobox
color = lightgrey
name = "Shigella"|

image_caption=Photomicrograph of "Shigella" sp. in a stool specimen
regnum = Bacteria
phylum = Proteobacteria
classis = Gamma Proteobacteria
ordo = Enterobacteriales
familia = Enterobacteriaceae
genus = "Shigella"
genus_authority = Castellani & Chalmers 1919
subdivision_ranks = Species
subdivision ="S. boydii"
"S. dysenteriae"
"S. flexneri"
"S. sonnei"

: "This article is about the bacteria. For the disease, see shigellosis"

"Shigella" is a genus of Gram-negative, non-spore forming rod-shaped bacteria closely related to "Escherichia coli" and "Salmonella". The causative agent of human shigellosis, "Shigella" cause disease in primates, but not in other mammals. [cite book | author = Ryan KJ, Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | publisher = McGraw Hill | year = 2004 |isbn = 0-8385-8529-9 ]

Classification

"Shigella" species are classified by four serogroups:

* Serogroup "A": "S. dysenteriae" (12 serotypes)
* Serogroup "B": "S. flexneri" (6 serotypes)
* Serogroup "C": "S. boydii" (23 serotypes)
* Serogroup "D": "S. sonnei" (1 serotype)

Group "A"–"C" are physiologically similar; "S. sonnei" (group "D") can be differentiated on the basis of biochemical metabolism assays. [cite book | author = Hale TL, Keusch GT | title = Shigella: Structure, Classification, and Antigenic Types. "in:" Baron's Medical Microbiology "(Baron S "et al", eds.)| edition = 4th ed. | publisher = Univ of Texas Medical Branch | year = 1996 | url = http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.1269 | isbn = 0-9631172-1-1 ] Three "Shigella" groups are the major disease-causing species: "S. flexneri" is the most frequently isolated species worldwide and accounts for 60% of cases in the developing world; "S. sonnei" causes 77% of cases in the developed world, compared to only 15% of cases in the developing world; and "S. dysenteriae" is usually the cause of epidemics of dysentery, particularly in confined populations such as refugee camps. [ [http://www.who.int/vaccine_research/diseases/diarrhoeal/en/index6.html World Health Organization. Shigellosis.] ]

Pathogenesis

"Shigella" infection is typically via ingestion (fecal–oral contamination); depending on age and condition of the host as few as ten bacterial cells can be enough to cause an infection. "Shigella" cause dysentery that results in the destruction of the epithelial cells of the intestinal mucosa in the cecum and rectum. Some strains produce enterotoxin and Shiga toxin, similar to the verotoxin of . [cite book | author = Hale TL, Keusch GT | title = Shigella. "in:" Baron's Medical Microbiology "(Baron S "et al", eds.)| edition = 4th ed. | publisher = Univ of Texas Medical Branch | year = 1996 | url = http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.chapter.1257 | isbn = 0-9631172-1-1 ] Both Shiga toxin and verotoxin are associated with causing hemolytic uremic syndrome.

"Shigella" invade the host through epithelial cells of the large intestine. Using a Type III secretion system acting as a biological syringe, the bacterium injects "IpaD" protein into cell, triggering bacterial invasion and the subsequent lysis of vacuolar membranes using "IpaB" and "IpaC" proteins. It utilizes a mechanism for its motility by which its "IcsA" protein triggers actin polymerization in the host cell (via N-WASP recruitment of Arp2/3 complexes) in a "rocket" propulsion fashion for cell-to-cell spread.

The most common symptoms are diarrhea, fever, nausea, vomiting, stomach cramps, flatulence, and straining to have a bowel movement. The stool may contain blood, mucus, or pus (e.g. dysentery). In rare cases, young children may have seizures. Symptoms can take as long as a week to show up, but most often begin two to four days after ingestion. Symptoms usually last for several days, but can last for weeks. Shigella is implicated as one of the pathogenic causes of reactive arthritis worldwide. [cite journal |author=Hill Gaston JS, Lillicrap MS |title=Arthritis associated with enteric infection |journal=Best practice & research. Clinical rheumatology |volume=17 |issue=2 |pages=219–39 |year=2003 |pmid=12787523|doi=10.1016/S1521-6942(02)00104-3]

Severe dysentery can be treated with ampicillin, TMP-SMX, or fluoroquinolones such as ciprofloxacin and of course rehydration.

Each of the "Shigella" genomes includes a virulence plasmid that encodes conserved primary virulence determinants. The "Shigella" chromosomes share most of their genes with that of "E. coli" K12 strain MG1655cite journal |author=Yang F "et al." |title=Genome dynamics and diversity of "Shigella" species, the etiologic agents of bacillary dysentery |journal=Nucleic Acids Res |volume=33 |issue=19 |pages=6445–58 |year=2005 |pmid=16275786 |doi=10.1093/nar/gki954]

External links

* Genome information is available at the [http://www.ericbrc.org NIAID Enteropathogen Resource Integration Center (ERIC)]

References

See also

*TSI slant, a selective test for enteric bacteria such as Shigella and Salmonella
*Infectious diarrhea
*Diarrheal diseases
*Traveler's diarrhea
*ETEC