Helicobacter pylori
From Free net encyclopedia
| Helicobacter pylori{{#if:{{{status|}}}| {{#switch:{{{status}}}
| se|SECURE|Secure|secure=Conservation status: Secure | dom|DOMESTICATED|Domesticated|domesticated=Conservation status: Domesticated | data|DD|DATA=Conservation status: Data deficient | lr=Conservation status: Lower risk | lc|LR/LC|LR/lc|lr/lc|LRLC|LRlc|lrlc=Conservation status: Lower risk (lc) | LR/nt|lr/nt|LRNT|LRnt|lrnt|NT|nt=Conservation status: Lower risk (nt) | LR/cd|lr/cd|LRCD|LRcd|lrcd=Conservation status: Lower risk (cd) | vu=Conservation status: Vulnerable | en=Conservation status: Endangered | cr=Conservation status: Critical | ew=Conservation status: Extinct in the wild | ex|EXTINCT|Extinct|extinct=Conservation status: Extinct{{#if:{{{extinct|}}}| ({{{extinct}}}) }} | Fossil|fossil=Conservation status: Fossil | pre=Conservation status: Prehistoric | Text|TEXT=Conservation status: See text | {{{status}}} }}}}Template:Subtext}|contents=Fossil range: {{{fossil_range|}}} }} |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| }}}|Image:EMpylori.jpg {{{image_caption|}}} }}{{#if:{{{image2|}}}|[[image:{{{image2}}}|{{{image2_width|200px}}}|{{{image2_caption|}}}]]{{{image2_caption|}}} }}
| ||||||||||||||||
| Scientific classification | ||||||||||||||||
|
| ||||||||||||||||
| {{{diversity|}}}Template:Section}|color=lightgrey|contents=Binomial name}}Template:Row}|style=style="text-align:center;"|contents=Helicobacter pylori {{{binomial_authority|}}}}}Template:Section}|color=lightgrey|contents=Trinomial name}}Template:Row}|style=style="text-align:center;"|contents={{{trinomial}}} {{{trinomial_authority|}}}}}Template:Section}|color=lightgrey|contents=Type Genus}}Template:Row}|style=style="text-align:center;"|contents={{{type_genus}}} {{{type_genus_authority|}}}}}Template:Section}|color=lightgrey|contents=Type Species}}Template:Row}|style=style="text-align:center;"|contents={{{type_species}}} {{{type_species_authority|}}}}}{{#if:{{{range_map|}}}|<tr><td>[[image:{{{range_map}}}|{{{range_map_width|200px}}}|{{{range_map_caption|}}}]] {{{range_map_caption|}}} }}Template:Row}|style=style="text-align:center;"|contents={{{binomial2}}}{{{binomial2_authority|}}}}}Template:Row}|style=style="text-align:center;"|contents={{{trinomial2}}} {{{trinomial2_authority|}}}}}{{#if:{{{range_map2|}}}|<tr><td>[[image:{{{range_map2}}}|{{{range_map2_width|200px}}}|{{{range_map2_caption|}}}]] {{{range_map2_caption|}}} }}Template:Row}|style=style="text-align:center;"|contents={{{binomial3}}}{{{binomial3_authority|}}}}}Template:Row}|style=style="text-align:center;"|contents={{{trinomial3}}} {{{trinomial3_authority|}}}}}{{#if:{{{range_map3|}}}|<tr><td>[[image:{{{range_map3}}}|{{{range_map3_width|200px}}}|{{{range_map3_caption|}}}]] {{{range_map3_caption|}}} }}Template:Row}|style=style="text-align:center;"|contents={{{binomial4}}}{{{binomial4_authority|}}}}}Template:Row}|style=style="text-align:center;"|contents={{{trinomial4}}} {{{trinomial4_authority|}}}}}{{#if:{{{range_map4|}}}|<tr><td>[[image:{{{range_map4}}}|{{{range_map4_width|200px}}}|{{{range_map4_caption|}}}]] {{{range_map4_caption|}}} }}Template:Section}|color=lightgrey|contents={{{subdivision_ranks}}}}}
| ||||||||||||||||
|
|
Helicobacter pylori is a bacterium that infects the mucus lining of the human stomach. Many peptic ulcers and some types of gastritis are caused by H. pylori infection, although most humans who are infected will never develop symptoms. This bacterium lives in the human stomach exclusively and is the only known organism that can thrive in that highly acidic environment. It is helix-shaped (hence the name helicobacter) and can literally screw itself into the stomach lining to colonizeTemplate:Ref.
Contents |
History
In 1875, German scientists found spiral bacteria in the lining of the human stomach; the bacteria could not be grown in culture and the results were eventually forgottenTemplate:Ref.
In 1892, the Italian researcher Giulio Bizzozero described spiral bacteria living in the acidic environment of the stomach of dogs.
Professor Walery Jaworski of the Jagiellonian University in Kraków investigated sediments of gastric washings obtained from humans in 1899. Among some rod-like bacteria, he also found bacteria with a characteristic spiral shape, which he called Vibrio rugula. He was the first to suggest a possible role of this organism in the pathogeny of gastric diseases. This work was included in the "Handbook of Gastric Diseases" but it did not have much impact as it was written in Polish. Jaworski was not able to culture the organismTemplate:Ref.
The bacterium was rediscovered in 1982 by two Australian scientists Robin Warren and Barry Marshall; they isolated the organisms from mucosal specimens from human stomachs and were the first to successfully culture themTemplate:Ref. In their original paper, Warren and Marshall contended that most stomach ulcers and gastritis were caused by colonization with this bacterium, not by stress or spicy food as had been assumed beforeTemplate:Ref.
The medical community was slow to recognize the role of this bacterium in stomach ulcers and gastritis, believing that no bacterium could survive for long in the acidic environment of the stomach. The community began to come around after further studies were done, including one in which Marshall drank a Petri dish of H. pylori, developed gastritis, and the bacteria were recovered from his stomach lining, thereby satisfying three out of the four Koch's postulates. Marshall's gastritis later resolved without treatment. Marshall and Warren went on to show that antibiotics are effective in the treatment of gastritis. In 1994, the National Institutes of Health published an opinion stating that most recurrent gastric ulcers were caused by H. pylori, and recommended that antibiotics be included in the treatment regimenTemplate:Ref. In 2005, Warren and Marshall were awarded the Nobel Prize in Medicine for their work on H. pyloriTemplate:Ref.
Before the appreciation of the bacterium's role, stomach ulcers were typically treated with medicines that neutralize stomach acid or decrease its production. While this worked well, the ulcers very often reappeared. A traditional medication against gastritis was bismuth subsalicylate. It was often effective, but fell out of use, since its mechanism of action was a mystery. Nowadays it is quite clear that it is due to the bismuth salt acting as an antibiotic. Today, many stomach ulcers are treated with antibiotics effective against H. pylori.
The bacterium was initially named Campylobacter pyloridis, then C. pylori (after a correction to the Latin grammar) and in 1989, after DNA sequencing and other data showed that the bacterium did not belong in the Campylobacter genus, it was placed in its own genus, Helicobacter. The name pylori comes from the Latin word pylorus, which means gatekeeper, and refers to the pyloric valve (the circular opening leading from the stomach into the duodenum).
While H. pylori remain the most important known bacteria to inhabit the human stomach, several other species of the Helicobacter genus have now been identified in other mammals and some birds, and some of these can infect humans. Helicobacter species have also been found to infect the livers of certain mammals and to cause liver disease.
Structure of the bacterium
H. pylori is a spiral-shaped gram-negative bacterium, about 3 micrometres long with a diameter of about 0.5 micrometre. It has 4-6 flagella. It is microaerophilic, i.e. it requires oxygen but at lower levels than those contained in the atmosphere. It uses hydrogen methanogenesis as an energy source. It tests positive for oxidase and catalase.
Image:Helicobacter Pylori Urease.png
With its flagella and its spiral shape, the bacterium drills into the mucus layer of the stomach, and then can either be found suspended in the gastric mucosa or attached to epithelial cells. It produces adhesins which bind to membrane-associated lipids and carbohydrates and help its adhesion to epithelial cells. It excretes the enzyme urease, which converts urea into ammonia and bicarbonate. The release of ammonia is beneficial to the bacterium since it partially neutralizes the very acidic environment of the stomach (whose very purpose is to kill bacteria). Ammonia is, however, toxic to the epithelial cells, and with other products of H. pylori, including protease, catalase, and phospholipases, causes damage to those cells.
A recent finding is that some strains of the bacteria have a particular mechanism for "injecting" the inflammatory agent peptidoglycan from their own cell wall into epithelial stomach cells. (See below for "cagA pathogenicity island" in the section "Genome studies of different strains".) It remains unknown how this mechanism is advantageous to the bacteriumTemplate:Ref.
Under conditions of environmental stress, Helicobacter will convert from the spiral to a coccoid form. This coccoid form of the organism has not been cultured, but has been found in the water supply in the US and is apparently involved in the epidemiology of the bacterium. The coccoid form has also been found to be able to adhere to gastric epithelial cells in vitro.
Infection and diagnosis
Infection may be symptomatic or asymptomatic (without visible ill effects). It is estimated that up to 70% of infection is asymptomatic.
The bacteria have been isolated from feces, saliva and dental plaque of infected patients, which suggests gastro-oral or fecal-oral as possible transmission routes.
It is estimated that about 2/3 of the world population are infected by the bacterium. Actual infection rates vary from nation to nation - the West (Western Europe, North America, Australasia) having rates around 25% and the Third World much higher. In the latter, it is common, probably due to poor sanitary conditions, to find infections in children. In the United States, infection is primarily in the older generations (about 50% for those over the age of 60 compared with 20% under 40 years) and the poorest. This is largely attributed to higher hygiene standards and widespread use of antibiotics. However, antibiotic resistance is appearing in H. pylori. There are already metronidazole resistant strains present in the UK population.
In the absence of antibiotic based treatments, H. pylori infection apparently persists for life; the human immune system is not able to eradicate it.
One can test for H. pylori infection with blood antibody or stool antigen tests, or with the carbon urea breath test (in which the patient drinks 14C- or 13C-labelled urea, which the bacterium metabolizes producing labelled carbon dioxide that can be detected in the breath), or endoscopy to provide a biopsy sample for testing for the presence of urease "rapid urease test", histology or microbial culture.
Treatment
Image:Pylorigastritis.jpg In patients who are asymptomatic, treatment is not usually recommended.
In gastric ulcer patients where H. pylori is detected, normal procedure is eradication to allow the ulcer to heal. The standard first-line therapy is a one week triple-therapy of amoxicillin, clarithromycin and omeprazole – though sometimes a different proton pump inhibitor is substituted, or metronidazole is used in place of amoxicillin in those allergic to penicillin. Such a therapy has revolutionised the treatment of gastric ulcers and has made a cure to the disease possible, where previously symptom-control using antacids, H2-antagonists or proton pump inhibitors alone was the only option.
Unfortunately, an increasing number of infected individuals are found to harbour bacteria resistant to first-line antibiotics. This results in initial treatment failure and requires additional rounds of antibiotic therapy. For resistant cases, a quadruple therapy may be used. Bismuth compounds are also effective in combination with the above drugs.
There is some preliminary evidence that regular consumption of broccoli might eradicate H. pyloriTemplate:Ref.
As explained below, some authors suggest that an H. pylori infection may be protective against certain diseases of the esophagus and cardia. Therefore, a more cautious approach than complete eradication may be necessary in some cases.
Gastric cancer connection
Gastric cancer and gastric MALT lymphoma (lymphoma of the mucosa-associated lymphoid tissue) have been associated with H. pylori, and the bacterium has been categorized as a group I carcinogen by the International Agency for Research on Cancer (IARC). While the association is reasonably strong, it is not entirely clear that there is a causal relationship involved.
Two related mechanisms by which H. pylori could promote cancer are under investigation. One mechanism involves the enhanced production of free radicals near H. pylori and an increased rate of host cell mutation. The other proposed mechanism has been called a "perigenetic pathway"Template:Ref and involves enhancement of the transformed host cell phenotype by means of alterations in cell proteins such as adhesion proteins. It has been proposed that H. pylori induces inflammation and locally high levels of TNF-alpha and/or interleukin 6. According to the proposed perigenetic mechanism, inflammation-associated signaling molecules such as TNF-alpha can alter gastric epithelial cell adhesion and lead to the dispersion and migration of mutated epithelial cells without the need for additional mutations in tumor suppressor genes such as genes that code for cell adhesion proteins.
Acid reflux and esophageal cancer
The infection rate with H. pylori has been decreasing in developing countries, presumably because of improved hygiene and increased antibiotics use. Accordingly, the incidence of gastric cancer in the U.S. has fallen by 80 percent from 1900 to 2000. However, gastroesophageal reflux disease (GORD or GERD depending on the use of British or American English, respectively) and cancer of the esophagus (BE: oesophagus) have increased dramatically during the same period. In 1996, Martin J. Blaser put forward the theory that H. pylori might also have a beneficial effect: by regulating the acidity of the stomach contents, it lowers the impact of regurgitation of stomach acids into the esophagus. While some favorable evidence has been accumulated, as of 2005 the theory is not universally accepted.
Genome studies of different strains
Image:Helicobacter pylori.jpg Several strains are known, and the genomes of two have been completely sequencedTemplate:Ref. The genome of the strain "26695" consists of about 1.7 million base pairs, with some 1550 genes. The two sequenced strains show large genetic differences, with up to 6% of the nucleotides differing.
Study of the H. pylori genome is centered on attempts to understand pathogenesis, the ability of this organism to cause disease. There are 62 genes in the "pathogenesis" category of the genome database. Both sequenced strains have an approximately 40 kb long Cag pathogenicity island (a common gene sequence believed responsible for pathogenesis) that contains over 40 genes. This pathogenicity island is usually absent from H. pylori strains isolated from humans who are carriers of H. pylori but remain asymptomatic.
The cagA gene codes for one of the major H. pylori virulence proteins. Bacterial strains that have the cagA gene are associated with an ability to cause severe ulcers. The cagA gene codes for a relatively long (1186 amino acid) protein. The CagA protein is transported into human cells where it may disrupt the normal functioning of the cytoskeleton. The Cag pathogenicity island has about 30 genes that code for a complex type IV secretion system. After attachment of H.pylori to stomach epithelial cells, the CagA protein is injected into the epithelial cells by the type IV secretion system. The CagA protein is phosphorylated on tyrosine residues by a host cell membrane-associated tyrosine kinase. Pathogenic strains of H. pylori have been shown to activate the epidermal growth factor receptor (EGFR), a membrane protein with a tyrosine kinase domain. Activation of the EGFR by H. pylori is associated with altered signal transduction and gene expression in host epithelial cells that may contribute to pathogenesis. It has also been suggested that a c-terminal region of the CagA protein (amino acids 873-1002) can regulate host cell gene transcription independent of protein tyrosine phosphorylation. It is thought, due to cagA's low GC content relative to the rest of the helicobacter genome, that the gene was acquired by horizontal transfer from another cagA+ bacterial species.
Each human population has a characteristic distribution of H. pylori strains that typically infect members of that population. This allows researchers to use H. pylori to study human migration patterns. It could be established that H. pylori in Amazon Indians has East Asian rather than European origins, suggesting that it arrived with the original immigrants at least 11,000 years ago.
See also
References
- Template:Note Template:Cite book
- Helicobacter Pylori and other Gastric Helicobacter-Like Organisms: direct link to appropriate section.
- Template:Note Template:Cite journal
- NB: link is to partial text unless subscribed
- Template:Note Template:Cite journal
- Template:Note Template:Cite journal
- Template:Note Template:Cite journal
- Template:Note Template:Cite web
- Template:Note The Nobel Prize in Physiology or Medicine 2005 awarded to Barry J. Marshall and J. Robin Warren "for their discovery of the bacterium Helicobacter pylori and its role in gastritis and peptic ulcer disease".
- Template:Note Template:Cite journal, PMID 15489856}}
- Template:Note Template:Cite journal
- Template:Note Template:Cite journal
- Template:Note The Pylori Gene website allows access to genome information for the H. pylori 26695 and J99 strains. Another genome interface is provided by the National Center for Biotechnology Information; 26695, J99.
External links
Template:Wikispecies Template:Commonscat
- The Helicobacter Foundation provides information on Helicobacter pylori and its effects - founded by Dr. Barry J. Marshall, one of the discoverers of H. pylori
- Helicobacter pylori persistence: biology and disease by Martin J. Blaser and John C. Atherton in Journal of Clinical Investigations (2004) Volume 113 pages 321–333.
- Helicobacter pylori: Physiology and Genetics Online text of the Mobley et al book (via NCBI).
- European Helicobacter Study Group sponsors annual international workshop, yearbook, and clinical guidelines
- The Year in Helicobacter pylori 2005 Helicobacter journal Sept 2005 - Free content
- The Year in Helicobacter pylori 2004 Helicobacter journal August 2004 - Free Content on line
- Atwood KC. Bacteria, Ulcers, and Ostracism?: H. pylori and the Making of a Myth. Skeptical Inquirer November 2004. Fulltext Claims that medicine’s purported ostracism of the discovery of H. pylori has achieved a mythological quality, but isn't true: after appropriate initial scientific skepticism, the hypothesis was accepted right "on schedule".
- Microscopic image of H. pylori
- List of species in the genus Helicobacter
Template:Featured articleTemplate:Link FA
zh-min-nan:Helicobacter pylori be:Helicobacter pylori da:Helicobacter pylori de:Helicobacter pylori es:Helicobacter pylori fr:Helicobacter pylori ko:헬리코박터 파일로리 it:Helicobacter pylori he:Helicobacter pylori lb:Helicobacter pylori nl:Helicobacter pylori ja:ヘリコバクター・ピロリ no:Helicobacter pylori nn:Helicobacter pylori pl:Helicobacter pylori pt:Helicobacter pylori ru:Helicobacter pylori fi:Helikobakteeri sv:Helicobacter pylori zh:幽門螺桿菌