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__NOTOC__
{{Taxobox
{{Taxobox
| color = lightgrey
| image = Clostridium_tetani_01.png
| name = ''Clostridium tetani''
| image = Clostridium_tetani_01.jpg
| image_width = 240px
| image_width = 240px
| image_caption = ''Clostridium tetani'' with characteristic 'tennis racket' appearance.
| image_caption = ''Clostridium tetani'' with characteristic 'tennis racket' appearance.
| regnum = [[Bacterium|Bacteria]]
| domain= [[Bacterium|Bacteria]]
| divisio = [[Firmicutes]]
| phylum = [[Firmicutes]]
| classis = [[Clostridia]]
| classis = [[Clostridia]]
| ordo = Clostridiales
| ordo = Clostridiales
Line 13: Line 12:
| species = '''''C. tetani'''''
| species = '''''C. tetani'''''
| binomial = ''Clostridium tetani''
| binomial = ''Clostridium tetani''
| binomial_authority = Flügge, 1886
| binomial_authority = Flügge, 1881
}}
}}
{{SI}}


{{Tetanus}}


{{About0|Tetanus}}


'''''Clostridium tetani''''' is a rod-shaped, anaerobic [[bacterium]] of the genus ''[[Clostridium]]''.  Like other ''Clostridium'' species, it is [[Gram-positive]], and its appearance on a [[gram stain]] resembles tennis rackets or drumsticks.<ref name=Sherris>{{cite book | author = Ryan KJ; Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | publisher = McGraw Hill | year = 2004 | id = ISBN 0838585299 }}</ref> ''C. tetani'' is found as [[endospore|spores]] in soil or as [[parasite]]s in the [[gastrointestinal tract]] of animals. ''C. tetani'' produces a potent biological toxin, [[tetanospasmin]], and is the causative agent of [[tetanus]].
{{SI}}
 
{{CMG}}
==Overview==
''Clostridium tetani'' is a rod-shaped, anaerobic [[bacterium]] of the genus ''[[Clostridium]]''.  Like other ''Clostridium'' species, it is [[Gram-positive]], and its appearance on a [[gram stain]] resembles tennis rackets or drumsticks.<ref name=Sherris>{{cite book | author = Ryan KJ; Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | publisher = McGraw Hill | year = 2004 | id = ISBN 0838585299 }}</ref> ''C. tetani'' is found as [[endospore|spores]] in soil or as [[parasite]]s in the [[gastrointestinal tract]] of animals. ''C. tetani'' produces a potent biological toxin, [[tetanospasmin]], and is the causative agent of [[tetanus]].
==Organism==
'''''Clostridium tetani''''' is a box-car shaped, [[Anaerobic organism|anaerobic]] [[bacterium]] of the genus species ''[[Clostridium]]''. Like other ''Clostridium'' genus species, it is [[Gram-positive]], and its appearance on a [[gram stain]] resembles [[tennis racket]]s or drumsticks.<ref name=Sherris>{{cite book |editor1-last=Ryan |editor1-first=KJ |editor2-last=Ray |editor2-first=CG | title = Sherris Medical Microbiology | edition = 4th | publisher = McGraw Hill | year = 2004 | isbn=0-8385-8529-9 }}</ref> ''C. tetani'' is found as [[endospore|spores]] in soil or in the [[gastrointestinal tract]] of animals. ''C. tetani'' produces a potent biological toxin, [[tetanospasmin]], and is the causative agent of [[tetanus]], a disease characterized by painful muscular spasms that can lead to respiratory failure and, in up to 40% of cases, death.
==History==
==History==
[[Tetanus]] was well known to ancient peoples, who recognized the relationship between wounds and fatal muscle spasms. In 1884, Arthur Nicolaier isolated the [[strychnine]]-like toxin of tetanus from free-living, anaerobic soil bacteria. The etiology of the disease was further elucidated in 1884 Antonio Carle and Giorgio Rattone, who demonstrated the transmissibility of tetanus for the first time. They produced tetanus in rabbits by injecting their sciatic nerve with pus from a fatal human tetanus case in that same year.
[[Tetanus]] was known to ancient people, who recognized the relationship between wounds and fatal muscle spasms. In 1884, [[Arthur Nicolaier]] isolated the [[strychnine]]-like toxin of tetanus from free-living, anaerobic soil bacteria. The etiology of the disease was further elucidated in 1890 by [[Antonie Carl]] and [[Giorgio Rattone]], who demonstrated the transmissibility of tetanus for the first time. They produced tetanus in rabbits by injecting their sciatic nerve with pus from a fatal human tetanus case in that same year.
In 1889, ''C. tetani'' was isolated from a human victim, by [[Kitasato Shibasaburo]], who later showed that the organism could produce disease when injected into animals, and that the toxin could be neutralized by specific [[antibodies]]. In 1897, [[Edmond Nocard]] showed that tetanus antitoxin induced [[passive immunity]] in humans, and could be used for [[prophylaxis]] and treatment. Tetanus toxoid [[vaccine]] was developed by P. Descombey in 1924, and was widely used to prevent tetanus induced by battle wounds during World War II.<ref name=CDC_2006>{{cite book | author = Atkinson W, Hamborsky J,                  McIntyre L, Wolfe S (eds). | title = Epidemiology               and Prevention of Vaccine-Preventable Diseases (The Pink               Book) | edition=9th ed.| publisher = Public Health                 Foundation | date = 2006 | url=http://www.cdc.gov/vaccines/pubs/pinkbook/downloads/tetanus.pdf}}</ref>
In 1889, ''C. tetani'' was isolated from a human victim, by [[Kitasato Shibasaburō]], who later showed that the organism could produce disease when injected into animals, and that the toxin could be neutralized by specific [[antibodies]]. In 1897, [[Edmond Nocard]] showed that tetanus antitoxin induced [[passive immunity]] in humans, and could be used for [[prophylaxis]] and treatment. Tetanus [[toxoid|toxoid vaccine]] was developed by P. Descombey in 1924, and was widely used to prevent tetanus induced by battle wounds during World War II.<ref name=CDC_2006>{{cite book |author=Centers for Disease Control and Prevention |editor1-last=Atkinson |editor1-first=W |editor2-last=Hamborsky |editor2-first=J |editor3-last=McIntyre |editor3-first=L |editor4-last=Wolfe |editor4-first=S | title = Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book) | edition=10th | publisher = Public Health Foundation | year = 2006 |chapter=Tetanus |chapterurl=http://www.cdc.gov/vaccines/pubs/pinkbook/downloads/tetanus.pdf}}</ref>
 
==Characteristics==
==Characteristics==
''C. tetani'' is a rod-shaped, obligate anaerobe which stains [[Gram positive]] in fresh cultures; established cultures may stain [[Gram negative]].<ref name=Sherris /> During vegetative growth, the organism cannot survive in the presence of [[oxygen]], is sensitive to heat and has [[Flagellum|flagella]] which provide limited mobility.   As the bacterium matures, it develops a terminal [[endospore|spore]], which gives the organism its characteristic appearance. ''C. tetani'' spores are extremely hardy, and are resistant to heat and most [[antiseptics]].<ref name=Brock>{{cite book | author = Madigan M; Martinko J (editors). | title = Brock Biology of Microorganisms | edition = 11th ed. | publisher = Prentice Hall | year = 2005 | id = ISBN 0131443291 }}</ref> The spores are distributed widely in [[manure]]-treated soils, and can also be found on human skin and in contaminated [[heroin]].<ref name=CDC_2006/>
''C. tetani'' is a rod-shaped, obligate anaerobe which stains [[Gram positive]] in fresh cultures; established cultures may stain [[Gram negative]].<ref name=Sherris /> During vegetative growth, the organism cannot survive in the presence of [[oxygen]], is heat-sensitive and exhibits [[Flagellum|flagellar]] [[motility]]. As the bacterium matures, it develops a terminal [[endospore|spore]], which gives the organism its characteristic appearance. ''C. tetani'' spores are extremely hardy as they are resistant to heat and most [[antiseptics]].<ref name=Brock>{{cite book |editor1-last=Madigan |editor1-first=M |editor2-last=Martinko |editor2-first=J | title = Brock Biology of Microorganisms | edition = 11th | publisher = Prentice Hall | year = 2005 | isbn=0-13-144329-1 }}</ref> The spores are distributed widely in [[manure]]-treated soils and can also be found on human skin.<ref name=CDC_2006/>
 
==Vaccination==
Tetanus can be prevented through the highly effective [[tetanus vaccine]], which is a tetanus toxin inactivated with formaldehyde to be [[immunogenic]] but not [[pathogen|pathogenic]]. The vaccine can be formulated as simple or adsorbed tetanus vaccine, combined tetanus and killed [[polio]] vaccine, or the older ([[diphtheria]], tetanus, [[pertussis]]) ([[DPT vaccine|DPT]]) vaccine. Side effects are rare, but if they do occur, include [[fever]], pain (sometimes long lasting) at the injection site, unexplained crying in infants, and irritability in older children or adults.
Severe reactions are extremely rare and include [[anaphylaxis]], [[seizure]]s and [[encephalopathy]]. All infants are recommended to receive the vaccine at 2, 4, 6, and 15 months of age {{Citation needed|date=April 2015}}.  A fifth booster dose should be given at 4–6 years of age (again, this needs a reference to the supporting data). After that, it should be given every 10 years. However, if a bite, scratch, or puncture occurs more than five years after the last dose of vaccine, the patients should receive another dose of vaccine.
==Toxicity==
==Toxicity==
''C. tetani'' usually enters a host through a wound to the skin, it then replicates and germinates spores. Once an infection is established, ''C. tetani'' produces two exotoxins, [[tetanolysin]] and [[tetanospasmin]]. Eleven strains of ''C. tetani'' have been identified, which differ primarily in flagellar [[antigen]]s and in its ability to produce tetanospasmin. The genes that produce toxin are encoded on a [[plasmid]] which is present in all toxigenic strains, and all strains that are capable of producing toxin produce identical toxins.<ref name= UW>Todar, Ken (2005) [http://www.bact.wisc.edu/themicrobialworld/clostridia.html Pathogenic Clostridia] Ken Todar's Microbial World. University of Wisconsin - Madison.</ref>
''C. tetani'' usually enters a host through a wound to the skin, then it replicates. High risk individuals are people exposed to soil or animal feces. The spores are widely distributed in soil and in the intestines and feces of horses, sheep, cattle, dogs, cats, rats, guinea pigs, and chickens. Manure-treated soil may contain large numbers of spores. In agricultural areas, a significant number of human adults may harbor the organism. The spores can also be found on skin surfaces and in contaminated heroin.<ref name=CDC_2006/> Once an infection is established, ''C. tetani'' produces two exotoxins, [[tetanolysin]] and [[tetanospasmin]]. Eleven strains of ''C. tetani'' have been identified, which differ primarily in flagellar [[antigen]]s and in their ability to produce tetanospasmin. The genes for toxin production are encoded on a [[plasmid]] which is present in all toxigenic strains, and all strains that are capable of producing toxin produce identical toxins.<ref name= UW>Todar, Ken (2005) [http://www.bact.wisc.edu/themicrobialworld/clostridia.html Pathogenic Clostridia], Ken Todar's Microbial World, [[University of Wisconsin at Madison|University of Wisconsin - Madison]].</ref>
 
Tetanolysin serves no known benefit to ''C. tetani''. Tetanospasmin is a [[neurotoxin]] that causes the clinical manifestations of tetanus. Tetanus toxin is generated in living bacteria, and is released when the bacteria [[lysis|lyse]], such as during spore germination or vegetative growth. A minimal amount of spore germination and vegetative cell growth are required for toxin production.<ref name= UW/>
Tetanolysin serves no known function to ''C. tetani'', and the reason the bacteria produce it is not known with certainty. Tetanospasmin is a [[neurotoxin]] and causes the clinical manifestations of tetanus. Tetanus toxin is generated in living bacteria, and is released when the bacteria lyses, such as during spore germination or during vegetative growth. A minimal amount of spore germination and vegetative cell growth are required for toxin production.<ref name= UW/>
Tetanus toxin is a potent neurotoxin. On the basis of weight, tetanospasmin is one of the most potent toxins known (based on tests conducted on mice). The estimated minimum human lethal dose is 2.5 [[nanogram]]s per kilogram of body weight, or 175 nanograms in a 70&nbsp;kg (154&nbsp;lb) human.<ref name=CDC_2006/> The only toxins more lethal to mice are [[botulinum toxin]], produced by close relative ''[[Clostridium botulinum]]'' and the [[Diphtheria toxin|exotoxin]] produced by ''[[Corynebacterium diphtheriae]]'', the causative agent of [[diphtheria]]. It should be noted, however, that humans and other animals may react to specific toxins differently from mice, and that the overall lethality of a specific toxin likely varies between different animals.
 
Tetanospasmin is a [[zinc]]-dependent [[metalloproteinase]] that is structurally similar to botulinum toxin, but with different effects. ''C. tetani'' synthesizes tetanospasmin as a single 150k[[Atomic mass unit|Da]] [[polypeptide]] progenitor toxin that is then cleaved by a [[protease]] into two fragments; fragment A (a 50k[[Dalton (unit)|Da]] "light chain") and fragment B (a 100 k[[Dalton (unit)|Da]] "heavy chain") which remain connected via a [[disulfide bond|disulfide bridge]]. Cleavage of the progenitor toxin into A and B fragments can be induced artificially by [[trypsin]].<ref name= UW/>
On the basis of weight, tetanospasmin is one of the most potent toxins known. The estimated minimum human lethal dose is 2.5 nanograms per [[kilogram]] of body weight, or 175 nanograms in a 70 kg (154 lb) human.<ref name=CDC_2006/> The only toxins more lethal to humans are [[botulinum toxin]], produced by ''[[Clostridium botulinum]]'' and the [[Diphtheria toxin|exotoxin]] produced by ''[[Corynebacterium diphtheriae]]'', the causative agent of [[diphtheria]].  
===Toxin action===
 
Tetanospasmin released in the wound is absorbed into the circulation and reaches the ends of motor neurons all over the body. The toxin acts at several sites within the [[central nervous system]], including [[nerve]] terminals, the [[spinal cord]], and [[brain]], and within the [[sympathetic nervous system]]. By binding to peripheral motor neuron terminals, the toxin enters the nerve axons, and is transported across [[synapse|synaptic junctions]] to the nerve-cell body in the brain stem and spinal cord by [[retrograde transport|retrograde intraneuronal transport]], until it reaches the central nervous system, where it rapidly binds to [[ganglioside]]s at the presynaptic membrane of inhibitory motor nerve endings.<ref name=CDC_2006/>
Tetanospasmin is a [[zinc]]-dependent [[metalloproteinase]], that is similar in structure to botulinum toxin, but each toxin produces quite different effects. ''C. tetani'' synthesizes tetanospasmin as a single 150k[[Atomic mass unit|Da]] [[polypeptide]] progenitor toxin, that is then cleaved by a [[protease]] into two fragments; fragment A (a 50kDa "light chain") and fragment B (a 100 kDa heavy chain) which remain connected via a disulfide bridge. Cleavage of the progenitor toxin into A and B fragments can also be induced artificially with trypsin.<ref name= UW/>  
The clinical manifestations of tetanus are caused when tetanus toxin blocks inhibitory impulses, by interfering with the release of [[neurotransmitter]]s, including [[glycine]] and [[gamma-aminobutyric acid]]. These inhibitory neurotransmitters inhibit the [[alpha motor neuron]]s. With diminished inhibition, the resting firing rate of the alpha motor neuron increases, producing rigidity, unopposed muscle contraction and spasm. Characteristic features are [[risus sardonicus]] (a rigid smile), [[trismus]] (commonly known as "lock-jaw"), and [[opisthotonus]] (rigid, arched back). [[Seizures]] may occur, and the [[autonomic nervous system]] may also be affected. Tetanospasmin appears to prevent the release of neurotransmitters by selectively cleaving a component of synaptic vesicles called [[synaptobrevin]] II.<ref name= UW/> Loss of inhibition also affects preganglionic sympathetic neurons in the lateral [[gray matter]] of the spinal cord and produces sympathetic hyperactivity and high circulating [[catecholamine]] levels. [[Hypertension]] and [[tachycardia]] alternating with [[hypotension]] and [[bradycardia]] may develop.<ref name="isbn0-07-146633-9">{{cite book |author=Loscalzo, Joseph; Fauci, Anthony S.; Braunwald, Eugene; Dennis L. Kasper; Hauser, Stephen L; Longo, Dan L. |title=Harrison's principles of internal medicine |publisher=McGraw-Hill Medical |year=2008 |isbn=0-07-146633-9 }}</ref><ref name="urlTetanus in Emergency Medicine">{{cite web |url=http://emedicine.medscape.com/article/786414-overview |title=Tetanus in Emergency Medicine |work=Emedicine |accessdate=2011-09-01}}</ref>
 
==Genome structure==
===Toxin Action===
''Clostridium tetani'' has a genome that contains 2.80 Mbp with 2,373 protein coding genes.<ref>{{Cite journal  | last1 = Bruggemann | first1 = H. | last2 = Baumer | first2 = S. | last3 = Fricke | first3 = WF. | last4 = Wiezer | first4 = A. | last5 = Liesegang | first5 = H. | last6 = Decker | first6 = I. | last7 = Herzberg | first7 = C. | last8 = Martinez-Arias | first8 = R. | last9 = Merkl | first9 = R. | last10 = Henne | first10 = A. | last11 = Gottschalk | first11 = G. | title = The genome sequence of Clostridium tetani, the causative agent of tetanus disease | journal = Proc Natl Acad Sci U S A | volume = 100 | issue = 3 | pages = 1316–21 |date=Feb 2003 | doi = 10.1073/pnas.0335853100 | pmid = 12552129 | pmc = 298770 | display-authors = 8 }}</ref>
Tetanospasmin is distributed in the blood and lymphatic system of the host. The toxin acts at several sites within the [[central nervous system]], including [[peripheral nerve]] terminals,
the [[spinal cord]], and [[brain]], and within the [[sympathetic nervous system]]. The toxin is taken up into within the nerve [[axon]] and transported across synaptic junctions, until it reaches the central nervous system, where it is rapidly fixed to [[ganglioside]]s at the presynaptic junctions of inhibitory motor nerve endings.<ref name=CDC_2006/>  
 
The clinical manifestations of tetanus are caused when tetanus toxin blocks inhibitory impulses, by interfering with the release of [[neurotransmitter]]s, including [[glycine]] and [[gamma-aminobutyric acid]]. This leads to unopposed muscle contraction and spasm. [[Seizures]] may occur, and the [[autonomic nervous system]] may also be affected. Tetanospasmin appears to prevent the release of neurotransmitters by selectively cleaving a component of synaptic vesicles called [[synaptobrevin]] II.<ref name= UW/>
 
==Treatment==
{{main|Tetanus}}
When a tetanus infection becomes established, treatment usually focuses on controlling muscle spasms, stopping toxin production, and neutralizing the effects of the toxin. Treatment includes administration of tetanus immune globulin (TIG), which comprises antibodies that inhibit tetanus toxin (also known as tetanus [[antitoxins]]), by binding to and removing unbound tetanus toxin from the body. Binding of the toxin to the nerve endings appears to be an irreversible event, and TIG is ineffective at removing bound toxin. Recovery of affected nerves requires the sprouting of a new axon terminal.<ref name= UW/> Large doses of antibiotic drugs (such as [[metronidazole]] or [[intramuscular]] [[penicillin]] G) are also given once tetanus infection is suspected, to halt toxin production.
 
Prevention of tetanus includes vaccination, and cleaning the primary wound. Prophylaxis is effective, in the form of a tetanus toxoid vaccine, which is given with or without [[passive immunization]] with tetanus immune globulin.  Very few cases of tetanus have occurred in individuals with up-to-date tetanus vaccinations. [[DTP vaccine]] (diphtheria-pertussis-tetanus) in North America, is given at 2, 4, 6, and 15–18 months of age, followed by a booster before entry to school (4-6 years). This regimen provides protection from tetanus for about 10 years, and every 10 years, thereafter a booster shot of tetanus vaccine is recommended.<ref name=CDC_2006/>
 
Tetanus is not contagious from person to person, and is the only vaccine-preventable disease that is [[infectious disease|infectious]] but not contagious. A ''C. tetani'' infection does not result in tetanus [[immunity (medical)|immunity]], and tetanus vaccination should be given as soon as the patient has stabilized.<ref name=CDC_2006/>


==References==
==References==
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===Further reading===
===Further reading===
* Clinical Microbiology, ISBN 0-940780-49-6
*{{cite book |title=Clinical Microbiogrophy |isbn=0-940780-49-6 }}


==External links==
==External links==
*[http://pathema.tigr.org/tigr-scripts/Clostridium/PathemaHomePage.cgi Pathema-''Clostridium'' Resource]
* [http://pathema.tigr.org/tigr-scripts/Clostridium/PathemaHomePage.cgi Pathema-''Clostridium'' Resource]
<br>[[cs:Clostridium tetani]]
*{{cite book |author=Centers for Disease Control and Prevention |chapter=Ch. 20: Tetanus |chapterurl=http://www.cdc.gov/vaccines/pubs/pinkbook/tetanus.html |editor1-last=Atkinson |editor1-first=W |editor2-last=Wolfe |editor2-first=S |editor3-last=Hamborsky |editor3-first=J |title=Epidemiology and Prevention of Vaccine-Preventable Diseases |publisher=Public Health Foundation |location=Washington DC |year=2012 |pages=291–300 |url=http://www.cdc.gov/vaccines/pubs/pinkbook/table-of-contents.html |edition=12th}}
[[de:Clostridium tetani]]
[[es:Clostridium tetani]]
[[fr:Clostridium tetani]]
[[he:Clostridium tetani]]
[[it:Clostridium tetani]]
[[nl:Clostridium tetani]]
[[ja:破傷風菌]]


[[Category:Clostridiaceae]]
[[Category:Clostridiaceae]]
[[Category:Infectious disease]]
[[Category:Gram-positive bacteria]]
[[Category:Bacterial diseases]]
[[Category:Tetanus]]
 
[[Category:Bacteria with sequenced genomes]]
[[pl:Laseczka tężca]]
[[tr:Clostridium tetani]]
 
 
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Latest revision as of 13:27, 5 June 2017

style="background:#Template:Taxobox colour;"|Template:Taxobox name
File:Clostridium tetani 01.png
Clostridium tetani with characteristic 'tennis racket' appearance.
style="background:#Template:Taxobox colour;" | Scientific classification
Domain: Bacteria
Phylum: Firmicutes
Class: Clostridia
Order: Clostridiales
Family: Clostridiaceae
Genus: Clostridium
Species: C. tetani
Binomial name
Clostridium tetani
Flügge, 1881

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Clostridium tetani is a rod-shaped, anaerobic bacterium of the genus Clostridium. Like other Clostridium species, it is Gram-positive, and its appearance on a gram stain resembles tennis rackets or drumsticks.[1] C. tetani is found as spores in soil or as parasites in the gastrointestinal tract of animals. C. tetani produces a potent biological toxin, tetanospasmin, and is the causative agent of tetanus.

Organism

Clostridium tetani is a box-car shaped, anaerobic bacterium of the genus species Clostridium. Like other Clostridium genus species, it is Gram-positive, and its appearance on a gram stain resembles tennis rackets or drumsticks.[1] C. tetani is found as spores in soil or in the gastrointestinal tract of animals. C. tetani produces a potent biological toxin, tetanospasmin, and is the causative agent of tetanus, a disease characterized by painful muscular spasms that can lead to respiratory failure and, in up to 40% of cases, death.

History

Tetanus was known to ancient people, who recognized the relationship between wounds and fatal muscle spasms. In 1884, Arthur Nicolaier isolated the strychnine-like toxin of tetanus from free-living, anaerobic soil bacteria. The etiology of the disease was further elucidated in 1890 by Antonie Carl and Giorgio Rattone, who demonstrated the transmissibility of tetanus for the first time. They produced tetanus in rabbits by injecting their sciatic nerve with pus from a fatal human tetanus case in that same year. In 1889, C. tetani was isolated from a human victim, by Kitasato Shibasaburō, who later showed that the organism could produce disease when injected into animals, and that the toxin could be neutralized by specific antibodies. In 1897, Edmond Nocard showed that tetanus antitoxin induced passive immunity in humans, and could be used for prophylaxis and treatment. Tetanus toxoid vaccine was developed by P. Descombey in 1924, and was widely used to prevent tetanus induced by battle wounds during World War II.[2]

Characteristics

C. tetani is a rod-shaped, obligate anaerobe which stains Gram positive in fresh cultures; established cultures may stain Gram negative.[1] During vegetative growth, the organism cannot survive in the presence of oxygen, is heat-sensitive and exhibits flagellar motility. As the bacterium matures, it develops a terminal spore, which gives the organism its characteristic appearance. C. tetani spores are extremely hardy as they are resistant to heat and most antiseptics.[3] The spores are distributed widely in manure-treated soils and can also be found on human skin.[2]

Vaccination

Tetanus can be prevented through the highly effective tetanus vaccine, which is a tetanus toxin inactivated with formaldehyde to be immunogenic but not pathogenic. The vaccine can be formulated as simple or adsorbed tetanus vaccine, combined tetanus and killed polio vaccine, or the older (diphtheria, tetanus, pertussis) (DPT) vaccine. Side effects are rare, but if they do occur, include fever, pain (sometimes long lasting) at the injection site, unexplained crying in infants, and irritability in older children or adults. Severe reactions are extremely rare and include anaphylaxis, seizures and encephalopathy. All infants are recommended to receive the vaccine at 2, 4, 6, and 15 months of age[citation needed]. A fifth booster dose should be given at 4–6 years of age (again, this needs a reference to the supporting data). After that, it should be given every 10 years. However, if a bite, scratch, or puncture occurs more than five years after the last dose of vaccine, the patients should receive another dose of vaccine.

Toxicity

C. tetani usually enters a host through a wound to the skin, then it replicates. High risk individuals are people exposed to soil or animal feces. The spores are widely distributed in soil and in the intestines and feces of horses, sheep, cattle, dogs, cats, rats, guinea pigs, and chickens. Manure-treated soil may contain large numbers of spores. In agricultural areas, a significant number of human adults may harbor the organism. The spores can also be found on skin surfaces and in contaminated heroin.[2] Once an infection is established, C. tetani produces two exotoxins, tetanolysin and tetanospasmin. Eleven strains of C. tetani have been identified, which differ primarily in flagellar antigens and in their ability to produce tetanospasmin. The genes for toxin production are encoded on a plasmid which is present in all toxigenic strains, and all strains that are capable of producing toxin produce identical toxins.[4] Tetanolysin serves no known benefit to C. tetani. Tetanospasmin is a neurotoxin that causes the clinical manifestations of tetanus. Tetanus toxin is generated in living bacteria, and is released when the bacteria lyse, such as during spore germination or vegetative growth. A minimal amount of spore germination and vegetative cell growth are required for toxin production.[4] Tetanus toxin is a potent neurotoxin. On the basis of weight, tetanospasmin is one of the most potent toxins known (based on tests conducted on mice). The estimated minimum human lethal dose is 2.5 nanograms per kilogram of body weight, or 175 nanograms in a 70 kg (154 lb) human.[2] The only toxins more lethal to mice are botulinum toxin, produced by close relative Clostridium botulinum and the exotoxin produced by Corynebacterium diphtheriae, the causative agent of diphtheria. It should be noted, however, that humans and other animals may react to specific toxins differently from mice, and that the overall lethality of a specific toxin likely varies between different animals. Tetanospasmin is a zinc-dependent metalloproteinase that is structurally similar to botulinum toxin, but with different effects. C. tetani synthesizes tetanospasmin as a single 150kDa polypeptide progenitor toxin that is then cleaved by a protease into two fragments; fragment A (a 50kDa "light chain") and fragment B (a 100 kDa "heavy chain") which remain connected via a disulfide bridge. Cleavage of the progenitor toxin into A and B fragments can be induced artificially by trypsin.[4]

Toxin action

Tetanospasmin released in the wound is absorbed into the circulation and reaches the ends of motor neurons all over the body. The toxin acts at several sites within the central nervous system, including nerve terminals, the spinal cord, and brain, and within the sympathetic nervous system. By binding to peripheral motor neuron terminals, the toxin enters the nerve axons, and is transported across synaptic junctions to the nerve-cell body in the brain stem and spinal cord by retrograde intraneuronal transport, until it reaches the central nervous system, where it rapidly binds to gangliosides at the presynaptic membrane of inhibitory motor nerve endings.[2] The clinical manifestations of tetanus are caused when tetanus toxin blocks inhibitory impulses, by interfering with the release of neurotransmitters, including glycine and gamma-aminobutyric acid. These inhibitory neurotransmitters inhibit the alpha motor neurons. With diminished inhibition, the resting firing rate of the alpha motor neuron increases, producing rigidity, unopposed muscle contraction and spasm. Characteristic features are risus sardonicus (a rigid smile), trismus (commonly known as "lock-jaw"), and opisthotonus (rigid, arched back). Seizures may occur, and the autonomic nervous system may also be affected. Tetanospasmin appears to prevent the release of neurotransmitters by selectively cleaving a component of synaptic vesicles called synaptobrevin II.[4] Loss of inhibition also affects preganglionic sympathetic neurons in the lateral gray matter of the spinal cord and produces sympathetic hyperactivity and high circulating catecholamine levels. Hypertension and tachycardia alternating with hypotension and bradycardia may develop.[5][6]

Genome structure

Clostridium tetani has a genome that contains 2.80 Mbp with 2,373 protein coding genes.[7]

References

  1. ↑ 1.0 1.1 1.2 Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed. ed.). McGraw Hill. ISBN 0838585299.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Centers for Disease Control and Prevention (2006). "Tetanus" (PDF). In Atkinson, W; Hamborsky, J; McIntyre, L; Wolfe, S. Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book) (10th ed.). Public Health Foundation.
  3. ↑ Madigan, M; Martinko, J, eds. (2005). Brock Biology of Microorganisms (11th ed.). Prentice Hall. ISBN 0-13-144329-1.
  4. ↑ 4.0 4.1 4.2 4.3 Todar, Ken (2005) Pathogenic Clostridia, Ken Todar's Microbial World, University of Wisconsin - Madison.
  5. ↑ Loscalzo, Joseph; Fauci, Anthony S.; Braunwald, Eugene; Dennis L. Kasper; Hauser, Stephen L; Longo, Dan L. (2008). Harrison's principles of internal medicine. McGraw-Hill Medical. ISBN 0-07-146633-9.
  6. ↑ "Tetanus in Emergency Medicine". Emedicine. Retrieved 2011-09-01.
  7. ↑ Bruggemann, H.; Baumer, S.; Fricke, WF.; Wiezer, A.; Liesegang, H.; Decker, I.; Herzberg, C.; Martinez-Arias, R.; et al. (Feb 2003). "The genome sequence of Clostridium tetani, the causative agent of tetanus disease". Proc Natl Acad Sci U S A. 100 (3): 1316–21. doi:10.1073/pnas.0335853100. PMC 298770. PMID 12552129.

Further reading

External links

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