Everything about Shigella totally explained
» 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 also cause disease in other
primates, but not in other mammals.
Classification
Shigella species are classified by four
serogroups:
Group
A–
C are physiologically similar;
S. sonnei (group
D) can be differentiated on the basis of biochemical metabolism assays.
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
E. coli O157:H7. 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, and straining to have a bowel movement. The stool may contain blood, mucus, or pus (for example 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.
Severe dysentery can be treated with
ampicillin,
TMP-SMX, or
fluoroquinolones such as
ciprofloxacin and of course rehydration.
Further Information
Get more info on 'Shigella'.
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