出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2016/08/20 12:48:42」(JST)
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顕微鏡で見たボツリヌス菌
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Clostridium botulinum van Ermengem 1896 |
ボツリヌス菌(学名:Clostridium botulinum)は、クロストリジウム属の細菌である。グラム陽性の大桿菌および偏性嫌気性菌。土の中に芽胞の形で広く存在する。菌は毒素の抗原性の違いによりA-Gの7種類の型に分類され、ヒトに対する中毒はA,B,E,F型で起こる。A、B型は芽胞の形で土壌中に分布し、C、E型は海底や湖沼に分布する。
ボツリヌスの語源はラテン語のbotulus(腸詰め、ソーセージ)であり、19世紀のヨーロッパでソーセージやハムを食べた人の間に起こる食中毒であったためこの名がついた。ハムやソーセージに発色剤として添加される硝酸塩は、発色作用よりもボツリヌス菌の繁殖を抑える目的で使用されている。1896年、ベルギーの医学者エミール・ヴァン・エルメンゲム (Emile van Ermengem) により発見・命名された。
当初はBacillus属と考えられたことから、botulusに形容詞語尾「-inus」を付け、"Bacillus botulinus"と命名された。広く使われるボツリヌス菌という呼び名はこの時の種形容語に由来する。学名はラテン語として扱われることから、1923年にClostridium属へと変更された際、中性名詞であるClostridiumに合わせて中性化され、現在はClostridium botulinumと呼ばれている。ラテン語としてみた場合、Clostridium botulinum(クローストリディウム・ボトゥリヌム)は「ソーセージのクロストリジウム菌」という意味を帯びる。
ボツリヌス菌が作り出すボツリヌス毒素(ボツリヌストキシン)は毒性が非常に強く、約0.5kgで世界人口分の致死量に相当するため、生物兵器として研究開発が行われた。炭疽菌を初めとする他の生物兵器同様、テロリストによる使用が懸念されている。
ボツリヌス毒素の致死量は体重70kgのヒトに対しA型毒素を吸入させた場合、0.7〜0.9μg[1]と考えられており、1gで約100万人分の致死量に相当する(ちなみに青酸カリは経口投与の場合5人/g)。自然界に存在する毒素としては最も強力である。
多くはボツリヌス毒素を含んだ食物を食べることで起こる。Clostridium botulinum が多く、まれにC. butyricum, C. baratli が原因菌となる。傷口にボツリヌス菌が感染して起こることもあるが、それほど多くはない。 腸管外科手術後や大量の抗生物質を服用し腸内細菌が著しく減少している場合は発症しやすくなる。
通常のボツリヌス症と異なり、ボツリヌス菌の芽胞を摂取することにより起こる。芽胞は乳児の体内で発芽し、ボツリヌス毒素を作り出す。原因となる食物は黒糖などいくつか考えられているが、蜂蜜について因果関係が明白になっている[2][3]。そのため、1歳未満の乳児に蜂蜜を与えてはならない[4](1987年10月20日厚生省通知)。芽胞は高温に耐える(下記参照)ため、一般的な加熱調理では蜂蜜中の芽胞の除去は困難である。この中毒が乳児特有である理由として、乳児は成人に比べ腸内細菌叢が未発達であることや、消化管が短いことから、成人では上部消化管で不活化されるボツリヌス菌が乳児では腸管まで届いてしまうためと考えられる。
ボツリヌス毒素は主に四肢の麻痺を引き起こす。重篤な場合は呼吸筋を麻痺させ死に至る。その他、複視・構音障害・排尿障害・発汗障害・喉の渇きがみられる。一方、発熱はほとんどなく、意識もはっきりしたままである。
乳児ボツリヌス症の場合、便秘などの消化器症状に続き、全身脱力が起きて首の据わりが悪くなる。
ボツリヌス菌は芽胞となって高温に耐えることができるが、ボツリヌス毒素自体は加熱することで不活化する。A、B型菌を不活化させるには100℃で6時間、芽胞で120℃で4分間の加熱が必要であるが、ボツリヌス毒素自体は100℃で1-2分の加熱で失活される[5]。このため、ボツリヌス菌による食中毒を防ぐには、食べる直前に食品を加熱することが効果的である。
中毒症状を発症した場合、抗毒素はウマ血清のみ(ただし、乳児ボツリヌス症では致死率が低いこともあり、一般的に使われない)。毒素の型毎に抗毒素もある。一般に「食餌性ボツリヌス症に対する抗毒素の投与は発症から24時間以内が望ましい」とされるが、24時間以上経過での投与でも効果が有ることが報告された。[6] ワクチンは研究者用にボツリヌストキソイドが開発されているが、中毒になってから用いても効果がない。また、米国においてボツリヌス免疫グロブリンが開発されている。
亜硝酸ナトリウムの添加は、ハム、ソーセージ、ベーコン、コンビーフ、すじこ、たらこなどの食品加工分野においては、ボツリヌス菌の増殖を抑制する効果があり、また、肉の血色素のヘモグロビンやミオグロビンに作用して、加熱処理により赤色を形成することから、広く使用されている[7]。
抗毒素製剤の備蓄の無い国に、抗毒素製剤を提供。
2006年7月12日、警察庁と産業技術総合研究所とでボツリヌス毒素を10分で検出する方法を共同開発した。(従来の方法では1-4日を要した。)新技術では糖とボツリヌス毒素を結合させ、レーザーで検出する。
感染症法に基づき、検査、治療、医薬品その他厚生労働省令で定める製品の製造又は試験研究目的にボツリヌス菌・毒素を所持する者は、「感染症発生予防規程の届出」「病原体等取扱主任者の選定」「教育訓練」等が義務づけられている。
ウィキメディア・コモンズには、ボツリヌス菌に関連するメディアがあります。 |
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Clostridium botulinum | |
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Clostridium botulinum stained with gentian violet. | |
Scientific classification | |
Class: | Clostridia |
Order: | Clostridiales |
Family: | Clostridiaceae |
Genus: | Clostridium |
Species: | C. botulinum |
Binomial name | |
Clostridium botulinum van Ermengem, 1896 |
Clostridium botulinum is a Gram-positive, rod-shaped, anaerobic, spore-forming, motile bacterium with the ability to produce the neurotoxin botulinum.[1][2] The botulinum toxin can cause a severe flaccid paralytic disease in humans and other animals[2] and is the most potent toxin known to mankind, natural or synthetic, with a lethal dose of 1.3–2.1 ng/kg in humans.[3]
C. botulinum is a diverse group of pathogenic bacteria initially grouped together by their ability to produce botulinum toxin and now known as four distinct groups, C. botulinum groups I-IV. C. botulinum groups I-IV, as well as some strains of Clostridium butyricum and Clostridium baratii, are the bacteria responsible for producing botulinum toxin.[1]
C. botulinum is responsible for foodborne botulism (ingestion of preformed toxin), infant botulism (intestinal infection with toxin-forming C. botulinum), and wound botulism (infection of a wound with C. botulinum). C. botulinum produces heat-resistant endospores that are commonly found in soil and are able to survive under adverse conditions.[1]
C. botulinum is a Gram-positive, rod-shaped, spore-forming bacterium. It is an obligate anaerobe, meaning that oxygen is poisonous to the cells. However, C. botulinum tolerates traces of oxygen due to the enzyme superoxide dismutase, which is an important antioxidant defense in nearly all cells exposed to oxygen.[4] C. botulinum is only able to produce the neurotoxin during sporulation, which can only happen in an anaerobic environment. Other bacterial species produce spores in an unfavorable growth environment to preserve the organism's viability and permit survival in a dormant state until the spores are exposed to favorable conditions.
C. botulinum is divided into four distinct phenotypic groups (I-IV) and is also classified into seven serotypes (A-G) based on the antigenicity of the botulinum toxin produced.[5][6]
The classification into groups is based on the ability of the organism to digest complex proteins.[7][8] Studies at the DNA and rRNA level support the subdivision of the species into groups I-IV. Most outbreaks of human botulism are caused by group I (proteolytic) or II (non-proteolytic) C. botulinum. Group III organisms mainly cause diseases in animals. Group IV C. botulinum has not been shown to cause human or animal disease.
Neurotoxin production is the unifying feature of the species. Seven types of toxins have been identified that are allocated a letter (A-G). All toxins are rapidly destroyed at 100 °C, but they are resistant to degradation by enzymes found in the gastrointestinal tract. This allows for ingested toxin to be absorbed from the intestines into the bloodstream.[3]
Most strains produce one type of neurotoxin, but strains producing multiple toxins have been described. C. botulinum producing B and F toxin types have been isolated from human botulism cases in New Mexico and California.[9] The toxin type has been designated Bf as the type B toxin was found in excess to the type F. Similarly, strains producing Ab and Af toxins have been reported. Evidence indicates the neurotoxin genes have been the subject of horizontal gene transfer, possibly from a viral source. This theory is supported by the presence of integration sites flanking the toxin in some strains of C. botulinum. However, these integrations sites are degraded, indicating that the C. botulinum acquired the toxin genes quite far in the evolutionary past.
Only botulinum toxin types A, B, E, and F cause disease in humans. Types A, B, and E are associated with foodborne illness, with type E specifically associated with fish products. Type C produces limberneck in birds and type D causes botulism in other mammals. No disease is associated with type G.[10] The "gold standard" for determining toxin type is a mouse bioassay, but the genes for types A, B, E, and F can now be readily differentiated using quantitative PCR.[11]
A few strains from organisms genetically identified as other Clostridium species have caused human botulism: C. butyricum has produced type E toxin[12] and C. baratii had produced type F toxin.[13][14] The ability of C. botulinum to naturally transfer neurotoxin genes to other clostridia is concerning, especially in the food industry, where preservation systems are designed to destroy or inhibit only C. botulinum but not other Clostridium species.
Properties |
Group I |
Group II |
Group III |
Group IV |
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Toxin Types |
A, B, F | B, E, F | C, D | G |
Proteolysis |
+ | – | weak | – |
Saccharolysis |
– | + | – | – |
Disease host |
human | human | animal | – |
Toxin gene |
chromosome/plasmid | chromosome/plasmid | bacteriophage | plasmid |
Close relatives |
C. sporogenes, C. putrificum | C. butyricum, C. beijerinickii | C. haemolyticum, C. novyi type A | C. subterminale, C. haemolyticum |
In the laboratory, C. botulinum is usually isolated in tryptose sulfite cycloserine (TSC) growth medium in an anaerobic environment with less than 2% oxygen. This can be achieved by several commercial kits that use a chemical reaction to replace O2 with CO2. C. botulinum is a lipase-positive microorganism that grows between pH of 4.8 and 7.0 and cannot use lactose as a primary carbon source, characteristics important for biochemical identification.[15]
C. botulinum was first recognized and isolated in 1895 by Emile van Ermengem from home-cured ham implicated in a botulism outbreak.[16] The isolate was originally named Bacillus botulinus, after the Latin word for sausage, botulus. ("Sausage poisoning" was a common problem in 18th- and 19th-century Germany, and was most likely caused by botulism)[17] However, isolates from subsequent outbreaks were always found to be anaerobic spore formers, so Ida A. Bengtson proposed that the organism be placed into the genus Clostridium, as the Bacillus genus was restricted to aerobic spore-forming rods.[18]
Since 1959, all species producing the botulinum neurotoxins (types A-G) have been designated C. botulinum. Substantial phenotypic and genotypic evidence exists to demonstrate heterogeneity within the species. This has led to the reclassification of C. botulinum type G strains as a new species, C. argentinense.[19]
Group I C. botulinum strains that do not produce a botulin toxin are referred to as C. sporogenes.[20]
The complete genome of C. botulinum has been sequenced at Wellcome Trust Sanger Institute in 2007.[21]
Botulism poisoning can occur due to preserved or home-canned, low-acid food that was not processed using correct preservation times and/or pressure.
Foodborne botulism "Signs and symptoms of foodborne botulism typically begin between 18 and 36 hours after the toxin gets into your body, but can range from a few hours to several days, depending on the amount of toxin ingested."[22]
Wound botulism Most people who develop wound botulism inject drugs several times a day, so it's difficult to determine how long it takes for signs and symptoms to develop after the toxin enters the body. Most common in people who inject black tar heroin, wound botulism signs and symptoms include:[22]
Infant botulism If infant botulism is related to food, such as honey, problems generally begin within 18 to 36 hours after the toxin enters the baby's body. Signs and symptoms include:
Beneficial effects of botulinum toxin: Purified botulinum toxin is diluted by a physician for treatment:
A number of quantitative surveys for C. botulinum spores in the environment have suggested a prevalence of specific toxin types in given geographic areas, which remain unexplained.
Type A C. botulinum predominates the soil samples from the western regions, while type B is the major type found in eastern areas.[24] The type-B organisms were of the proteolytic type I. Sediments from the Great Lakes region were surveyed after outbreaks of botulism among commercially reared fish, and only type E spores were detected.[25][26][27] In a survey, type-A strains were isolated from soils that were neutral to alkaline (average pH 7.5), while type-B strains were isolated from slightly acidic soils (average pH 6.25).
C. botulinum type E is prevalent in aquatic sediments in Norway and Sweden,[28] Denmark,[29] the Netherlands, the Baltic coast of Poland, and Russia.[24] The type-E C. botulinum was suggested to be a true aquatic organism, which was indicated by the correlation between the level of type-E contamination and flooding of the land with seawater. As the land dried, the level of type E decreased and type B became dominant.
In soil and sediment from the United Kingdom, C. botulinum type B predominates. In general, the incidence is usually lower in soil than in sediment. In Italy, a survey conducted in the vicinity of Rome found a low level of contamination; all strains were proteolytic C. botulinum types A or B.[30]
C. botulinum type A was found to be present in soil samples from mountain areas of Victoria.[31] Type-B organisms were detected in marine mud from Tasmania.[32] [Needs Source Checked] Type-A C. botulinum has been found in Sydney suburbs and types A and B were isolated from urban areas. In a well-defined area of the Darling-Downs region of Queensland, a study showed the prevalence and persistence of C. botulinum type B after many cases of botulism in horses.
A "mouse protection" or "mouse bioassay" test determines the type of C. botulinum toxin present using monoclonal antibodies. An enzyme-linked immunosorbent assay (ELISA)with digoxigenin-labeled antibodies can also be used to detect the toxin,[33] and quantitative PCR can detect the toxin genes in the organism.[11]
C. botulinum is also used to prepare the medicaments Botox, Dysport, Xeomin, and Neurobloc used to selectively paralyze muscles to temporarily relieve muscle function. It has other "off-label" medical purposes, such as treating severe facial pain, such as that caused by trigeminal neuralgia.
Botulin toxin produced by C. botulinum is often believed to be a potential bioweapon as it is so potent that it takes about 75 nanograms to kill a person (LD50 of 1 ng/kg,[34] assuming an average person weighs ~75 kg); 1 kilogram of it would be enough to kill the entire human population. For comparative purposes, a quarter of a typical grain of sand's weight (350 ng) of botulinum toxin would constitute a lethal dose for humans.
C. botulinum is a soil bacterium. The spores can survive in most environments and are very hard to kill. They can survive the temperature of boiling water at sea level, thus many foods are canned with a pressurized boil that achieves even higher temperatures, sufficient to kill the spores.
Growth of the bacterium can be prevented by high acidity, high ratio of dissolved sugar, high levels of oxygen, very low levels of moisture, or storage at temperatures below 3 °C (38 °F) for type A. For example, in a low-acid, canned vegetable such as green beans that are not heated enough to kill the spores (i.e., a pressurized environment) may provide an oxygen-free medium for the spores to grow and produce the toxin. However, pickles are sufficiently acidic to prevent growth; even if the spores are present, they pose no danger to the consumer. Honey, corn syrup, and other sweeteners may contain spores, but the spores cannot grow in a highly concentrated sugar solution; however, when a sweetener is diluted in the low-oxygen, low-acid digestive system of an infant, the spores can grow and produce toxin. As soon as infants begin eating solid food, the digestive juices become too acidic for the bacterium to grow.
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Bacilli |
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Clostridia |
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Mollicutes |
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Authority control |
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リンク元 | 「細菌」「ボツリヌス症」「クロストリジウム属」 |
関連記事 | 「clostridium」「botulin」「Clostridium」 |
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