Shigella dysenteriae
Encyclopedia
Shigella dysenteriae is a species of the rod-shaped bacteria
l genus
Shigella
. Shigella can cause shigellosis
(bacillary dysentery
). Shigellae are Gram-negative
, non-spore-forming
, facultatively anaerobic
, non-motile
bacteria.
S. dysenteriae, spread by contaminated water and food, causes the most severe dysentery
because of its potent and deadly Shiga toxin
, but other species may also be dysentery agents. Contamination is often caused by bacteria on unwashed hands during food preparation, or soiled hands reaching the mouth .
, malnutrition
, rectal prolapse
, tenesmus
, reactive arthritis
, and CNS
problems. Further, Shigella dysenteriae is associated with the development of Hemolytic uremic syndrome, which includes anemia
, thrombocytopenia
, and renal failure
.
, DCA agar
, or HE agar
are inoculated and colonies are colorless on all of them as the organism is a non-lactose
fermentor. Inoculation of a TSI slant
shows an alkaline slant and acidic but with no gas or H2S production. Following incubation on SIM, the culture appears non-motile with no H2S production. Addition of Kovac's reagent
to the SIM tube following growth typically indicates no indole
formation (serotypes 2, 7 and 8 produce indole).
It's noteworthy that Shigella flexneri
will produce acid and gas from glucose, and Shigella sonnei
is mannitol
and ornithine
positive, and is also late lactose fermentor (ONPG positive). Some Shigella
species are capable of producing indole
.
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
l genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Shigella
Shigella
Shigella is a genus of Gram-negative, nonspore forming, non-motile, rod-shaped bacteria closely related to Escherichia coli and Salmonella. The causative agent of human shigellosis, Shigella causes disease in primates, but not in other mammals. It is only naturally found in humans and apes. During...
. Shigella can cause shigellosis
Shigellosis
Shigellosis, also known as bacillary dysentery or Marlow Syndrome, in its most severe manifestation, is a foodborne illness caused by infection by bacteria of the genus Shigella. Shigellosis rarely occurs in animals other than humans and other primates like monkeys and chimpanzees...
(bacillary dysentery
Dysentery
Dysentery is an inflammatory disorder of the intestine, especially of the colon, that results in severe diarrhea containing mucus and/or blood in the faeces with fever and abdominal pain. If left untreated, dysentery can be fatal.There are differences between dysentery and normal bloody diarrhoea...
). Shigellae are Gram-negative
Gram-negative
Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...
, non-spore-forming
Endospore
An endospore is a dormant, tough, and temporarily non-reproductive structure produced by certain bacteria from the Firmicute phylum. The name "endospore" is suggestive of a spore or seed-like form , but it is not a true spore . It is a stripped-down, dormant form to which the bacterium can reduce...
, facultatively anaerobic
Facultative anaerobic organism
A facultative anaerobic organism is an organism, usually a bacterium, that makes ATP by aerobic respiration if oxygen is present but is also capable of switching to fermentation...
, non-motile
Motility
Motility is a biological term which refers to the ability to move spontaneously and actively, consuming energy in the process. Most animals are motile but the term applies to single-celled and simple multicellular organisms, as well as to some mechanisms of fluid flow in multicellular organs, in...
bacteria.
S. dysenteriae, spread by contaminated water and food, causes the most severe dysentery
Dysentery
Dysentery is an inflammatory disorder of the intestine, especially of the colon, that results in severe diarrhea containing mucus and/or blood in the faeces with fever and abdominal pain. If left untreated, dysentery can be fatal.There are differences between dysentery and normal bloody diarrhoea...
because of its potent and deadly Shiga toxin
Shiga toxin
Shiga toxins are a family of related toxins with two major groups, Stx1 and Stx2, whose genes are considered to be part of the genome of lambdoid prophages. The toxins are named for Kiyoshi Shiga, who first described the bacterial origin of dysentery caused by Shigella dysenteriae. The most common...
, but other species may also be dysentery agents. Contamination is often caused by bacteria on unwashed hands during food preparation, or soiled hands reaching the mouth .
Signs and Symptoms
The most commonly observed signs associated with Shigella dysentery include colitisColitis
In medicine, colitis refers to an inflammation of the colon and is often used to describe an inflammation of the large intestine .Colitides may be acute and self-limited or chronic, i.e...
, malnutrition
Malnutrition
Malnutrition is the condition that results from taking an unbalanced diet in which certain nutrients are lacking, in excess , or in the wrong proportions....
, rectal prolapse
Rectal prolapse
Rectal prolapse normally describes a medical condition wherein the walls of the rectum protrude through the anus and hence become visible outside the body.-Types:There are three chief conditions which come under the title rectal prolapse:...
, tenesmus
Tenesmus
Rectal tenesmus is a feeling of incomplete defecation. It is experienced as an inability or difficulty to empty the bowel at defecation...
, reactive arthritis
Arthritis
Arthritis is a form of joint disorder that involves inflammation of one or more joints....
, and CNS
CNS
-Science and medicine:* Cell, Nature, and Science, the three most prestigious scientific journals involved in biomedical research* Central nervous system, brain and spinal cord* Chronic nonbacterial prostatitis, a pelvic pain condition affecting men...
problems. Further, Shigella dysenteriae is associated with the development of Hemolytic uremic syndrome, which includes anemia
Anemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
, thrombocytopenia
Thrombocytopenia
Thrombocytopenia is a relative decrease of platelets in blood.A normal human platelet count ranges from 150,000 to 450,000 platelets per microliter of blood. These limits are determined by the 2.5th lower and upper percentile, so values outside this range do not necessarily indicate disease...
, and renal failure
Renal failure
Renal failure or kidney failure describes a medical condition in which the kidneys fail to adequately filter toxins and waste products from the blood...
.
Diagnosis
Since the specimen is not sterile, the use of selective plates is mandatory. XLD agarXLD agar
Xylose lysine deoxycholate agar is a selective growth medium used in the isolation of Salmonella and Shigella species from clinical samples and from food. It has a pH of approximately 7.4, leaving it with a bright pink or red appearance due to the indicator phenol red. Sugar fermentation lowers...
, DCA agar
DCA agar
DCA agar - Deoxycholate Citrate Agar is a solid bacteriological growth medium.-Uses:It is particularly useful for the isolation of organisms that cause bacilliary dysentery, salmonella strains that cause food poisoning and Salmonella Paratyphi. It is not so selective for Salmonella Typhi...
, or HE agar
Hektoen enteric agar
Hektoen enteric agar is a selective and differential agar primarily used to recover Salmonella and Shigella from patient specimens. HE contains indicators of lactose fermentation and H2S production; as well as inhibitors to prevent the growth of gram positive bacteria...
are inoculated and colonies are colorless on all of them as the organism is a non-lactose
Lactose
Lactose is a disaccharide sugar that is found most notably in milk and is formed from galactose and glucose. Lactose makes up around 2~8% of milk , although the amount varies among species and individuals. It is extracted from sweet or sour whey. The name comes from or , the Latin word for milk,...
fermentor. Inoculation of a TSI slant
TSI slant
thumb|right|250px|TSI agar slant results: preinoculated ,[[Pseudomonas aeruginosa|P. aeruginosa]], [[Escherichia coli|E...
shows an alkaline slant and acidic but with no gas or H2S production. Following incubation on SIM, the culture appears non-motile with no H2S production. Addition of Kovac's reagent
Indole test
The indole test is a biochemical test performed on bacterial species to determine the ability of the organism to split indole from the amino acid tryptophan...
to the SIM tube following growth typically indicates no indole
Indole
Indole is an aromatic heterocyclic organic compound. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring. Indole is a popular component of fragrances and the precursor to many pharmaceuticals. Compounds that contain an...
formation (serotypes 2, 7 and 8 produce indole).
It's noteworthy that Shigella flexneri
Shigella 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...
will produce acid and gas from glucose, and Shigella sonnei
Shigella sonnei
Shigella sonnei is a species of Shigella. Together with Shigella flexneri, it is responsible for 90% of shigellosis. Shigella sonnei is named for the Danish bacteriologist Carl Olaf Sonne....
is mannitol
Mannitol
Mannitol is a white, crystalline organic compound with the formula . This polyol is used as an osmotic diuretic agent and a weak renal vasodilator...
and ornithine
Ornithine
Ornithine is an amino acid that plays a role in the urea cycle.-Role in urea cycle:L-Ornithine is one of the products of the action of the enzyme arginase on L-arginine, creating urea. Therefore, ornithine is a central part of the urea cycle, which allows for the disposal of excess nitrogen....
positive, and is also late lactose fermentor (ONPG positive). Some Shigella
Shigella
Shigella is a genus of Gram-negative, nonspore forming, non-motile, rod-shaped bacteria closely related to Escherichia coli and Salmonella. The causative agent of human shigellosis, Shigella causes disease in primates, but not in other mammals. It is only naturally found in humans and apes. During...
species are capable of producing indole
Indole
Indole is an aromatic heterocyclic organic compound. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring. Indole is a popular component of fragrances and the precursor to many pharmaceuticals. Compounds that contain an...
.