SHIGELLA
Shigella is a genus of gamma proteobacteria
in the family Enterobacteriaceae. Shigellae
are Gram-negative, nonmotile, non-spore
forming, rod-shaped bacteria, very closely
related to Escherichia coli.
Shigella were discovered over 100 years ago by
the Japanese microbiologist, Shiga, for whom the
genus is named. There are four species of
Shigella: S. boydii, S. dysenteriae, S. flexneri,
and S. sonnei. Shigella sonnei, also known as
Group D Shigella, accounts for over two-thirds of
the shigellosis in the United States.
Shigella flexneri, or Group B Shigella, accounts
for almost all of the rest. Other types of Shigella
are rare in this country, although they are
important causes of disease in the developing
world.
Figure:
Several media have been
designed to selectively grow
enteric bacteria and allow
differentiation of Salmonella
and Shigella from E. coli.
The primary plating media
shown here are eosin
methylene blue (EMB) agar,
MacConkey agar, ENDO
agar, Hektoen enteric (HE)
agar and SalmonellaShigella (SS) agar.
http://www.textbookofbacteriolog
y.net/Shigella.html
IDENTIFICATION
S.Dysenteriae is a facultative anaerobic, rodshaped bacteria.
Laboratory indicators:
non-motile
Lysine: Lactose: anaerogenic (no gas production from
carbohydrates)
http://microbes.historique.net/dysenteriae.html
Bacteria (domain); Proteobacteria (phylum);
Gamma Proteobacteria (class);
Enterobacteriales (order); Enterobacteriaceae
(family); Shigella (genus); Shigella boydii
(spesies)
Shigella boydii is a bacillary (rod-shaped)
gram-negative bacterium that does not form
spores and is usually nonmotile.
Habitat: S. boydii inhabits the intestine and
rectum of humans and other primates. It can
survive in feces and soil and/or food/water
contaminated with fecal matter. For example,
in Guadalajara, Mexico, Salmonella and
Shigella species were found in freshly
squeezed orange juice, oranges, and wiping
cloths found in public markets and street
booths.
Cell Structure: Shigella's structural characteristics follow that of
Gram-negative bacteria. Most research would agree that Shigella
are nonmotile but some evidence suggests that they do in fact
have flagella, although motility is not necessary for infection of
intestine. The flagella tend to be on one pole of the cell and about
10 microns in length and 12-14nm in diameter.
Metabolism: S. boydii, when found in the intestine, go though
anaerobic metabolic pathways but can survive outside of the body
due to its ability to utilize aerobic pathways. More specifically, S.
boydii, typically does not have oxidase enzymes but rather
catalase enzymes.
Methyl red testing is positive, meaning that the bacteria uses a
mixed acid fermentation pathway.
Voges–Proskauer and Simmons’ citrate reactions are negative,
meaning that this organism does not utilize the butylene glycol
pathway or produce acetoin. Lysine decarboxylase, arginine
dihydrolase and ornithine decarboxylase are not present. S. boydii
does not produce H2S, does not hydrolyze urea. Carbohydrates
are usually fermented and these include glucose (in the absence
of gas production), D-mannitol, arabinose, trehalose and
mannose.
http://www.microbewiki.kenyon.edu
Domain: Bacteria Phylum: Proteobacteria Class:
Gamma proteobacteria Order: Enterobacteriales
Family: Enterobacteriaceae Genus: Shigella
Species:Shigella sonnei.
Shigella sonnei is a non-motile (don’t have flagella),
nonspore-forming, facultative anaerobic Gram-negative
bacterium. Shigella sonnei is a rod-shape bacterium
and is lactose-fermenting bacterium causing dysentery.
Shigella sonnei is extremely fragile in experimental
settings. Its natural habitat is in a low pH environment
such as the human gastrointestinal tract. Its optimal
environmental temperature is 37 degrees Celsius,
similar to the temperature in the human body.
Therefore, human’s gastrointestinal tract appears to be
the only found natural host of Shigella sonnei that we
know so far.
Domain:Bacteria, Phylum:Proteobacteria, Class:Gamma
Proteobacteria, Order:Enterobacteriales,
Family:Enterobacteriaceae, Genus:Shigella,
Species:S. flexneri
Shigella flexneri is a species of Gram-negative bacteria in the
genus Shigella that can cause diarrhea in humans. There are
several different serogroups of Shigella; S. flexneri belongs to
group B.
S. flexneri infections can usually be treated with antibiotics
although some strains have become resistant.
Shigella flexneri is a non-motile, non-spore forming, rod-shaped
bacterium that is physiologically similar to Shigella dysenteriae, Shigella
boydii, and Escherichia coli.
It is important because it causes shigellosis, an acute bloody diarrhea.
Shigella flexneri is the most common cause of the endemic form of
shigellosis, and the endemic form is the cause of most Shigellosis-related
deaths.
While not much of a problem in developed countries, Shigella flexneri
(specifically Shigella flexneri 2a) is a major public health concern in
developing countries. Shigella was recognized as the cause of bacillary
dysentery in the 1890s by Shiga, hence the genus name (Nato et al.).
Shigella flexneri 2a strain 301 was isolated and sequenced by Jin et al.
They isolated the bacterium from a shigellosis patient in China in 1984.
Shigella flexneri is a facultative anaerobe. It makes ATP via
aerobic respiration in the presence of oxygen and via
fermentation in the absence of oxygen. Although it is closely
related to Escherichia coli, Shigella flexneri can be
differentiated because it fails to ferment lactose or
decarboxylate lysine (Jin et al.)
Shigella flexneri is prevalent in developing countries because
sanitation is poor. The bacterium is found in the feces of
infected individuals, so water polluted with feces can act as a
route of infection (Huang and Zhou).