HELICOBACTER PYLORI

'''Helicobacter pylori''' is a helical shaped Gram-negative bacterium that infects various areas of the stomach and duodenum. Many cases of peptic ulcers, gastritis, duodenitis, and perhaps some cancer are caused by ''H. pylori'' infection. However, many who are infected do not show any symptoms of disease. ''Helicobacter'' spp. are the only known microorganisms that can thrive in the highly acidic environment of the stomach. Its helical shape (from which the genus name is derived) is thought to have evolved to penetrate and favor its motility in the mucus gel layer.^[1]

Contents

History

Structure

Colonization

Diagnosis of infection

Treatment of infection

''Helicobacter'' and cancer

Genome studies of different strains

See also

Notes

References

External links

History

In 1875, German scientists found helical shaped bacteria in the lining of the human stomach. The bacteria could not be grown in culture and the results were eventually forgotten. An Endangered Species in the Stomach, Blaser MJ, , , Scientific American, 2005
In 1893, the Italian researcher Giulio Bizzozero described helical shaped 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 helical 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.^[2]
The bacterium was rediscovered in 1979 by Australian pathologist Robin Warren, who did further research on it with Barry Marshall beginning in 1981; they isolated the organisms from mucosal specimens from human stomachs and were the first to successfully culture them.^[3] In their original paper,^[4] Warren and Marshall contended that most stomach ulcers and gastritis were caused by infection by this bacterium and not by stress or spicy food as had been assumed before.^[5]
The medical community was slow to recognize the role of this bacterium in stomach ulcers and gastritis, believing that no microorganism 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. The fourth was satisfied after a second endoscopy ten days after inoculation revealed signs of gastritis and the presence of "H. pylori". Marshall was then able to treat himself using a fourteen day dual therapy with bismuth salts and metronidazole. Marshall and Warren went on to show that antibiotics are effective in the treatment of many cases of gastritis. In 1994, the National Institutes of Health (USA) published an opinion stating that most recurrent gastric ulcers were caused by ''H. pylori'', and recommended that antibiotics be included in the treatment regimen.^[6] Evidence has been accumulating to suggest that duodenal ulcers are also associated with ''H. pylori'' infection.^[7][8] In 2005, Warren and Marshall were awarded the Nobel Prize in Medicine for their work on ''H. pylori''.^[9]
Before the appreciation of the bacterium's role, stomach ulcers were typically treated with medicines that neutralize gastric acid or decrease its production. While this worked well, the ulcers very often reappeared. A very often used medication against gastritis and peptic ulcers 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 ''pylōri'' means "of the pylorus" or pyloric valve (the circular opening leading from the stomach into the duodenum), from the Greek word ''πυλωρός'', which means gatekeeper.
While ''H. pylori'' remains the most medically important bacterial inhabitant of the human stomach, other species of the ''Helicobacter'' genus have 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. ''Helicobacter'' and digestive malignancies, Starzyñska T, Malfertheiner P, , , Helicobacter, 2006

Structure

''H. pylori'' is a helical 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 contains a hydrogenase which can be used to obtain energy by oxidizing molecular hydrogen (H₂) that is produced by other intestinal bacteria.^[10] It tests positive for oxidase, catalase, and urease. It is capable of forming biofilms^[11] and conversion from helical to coccoid form^[12], both likely to favor its survival and be factors in the epidemiology of the bacterium. The coccoid form of the organism has not been cultured, but has been found in the water supply in the US. This form has also been found to be able to adhere to gastric epithelial cells ''in vitro''.

Colonization

With its flagella, the bacterium moves through the stomach lumen and drills into the mucus gel layer of the stomach. It then finds ways to live in various areas of the stomach. The known areas include: inside the mucus gel layer (with a preference for the superficial area), above epithelial cells, and inside vacuoles formed by ''H. pylori'' in epithelial cells. It produces adhesins which bind to membrane-associated lipids and carbohydrates and help its adhesion to epithelial cells. It produces large amounts of urease enzymes which are localized inside and outside of the bacterium. Urease metabolizes urea (which is normally secreted into the stomach) to carbon dioxide and ammonia which neutralizes gastric acid. The survival of ''H. pylori'' in the acidic stomach is dependant on urease, and it would eventually die without it. The ammonia that is produced is toxic to the epithelial cells, and with other products of ''H. pylori'', including protease, catalase, and phospholipases, causes damage to those cells.
Some strains of the bacteria have a particular mechanism for "injecting" the inflammatory inducing 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) This factor may play a role in allowing certain strains to invade host tissue.^[13]

Diagnosis of infection

Diagnosis of infection is usually made by checking for dyspepetic symptoms and then doing tests which can suggest ''H. pylori'' infection. One can test noninvasively for ''H. pylori'' infection with a blood antibody test, stool antigen test, 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). However, the most reliable method for detecting ''H .pylori'' infection is a biopsy check during endoscopy with a rapid urease test, histological examination, and microbial culture. Except for the biopsy check, none of the test methods are completely failsafe. Blood antibody tests, for example, range from 76% to 84% sensitivity. Some drugs can affect ''H. pylori'' urease activity and give "false negatives" with the urea-based tests.
Infection may be symptomatic or asymptomatic (without perceptible ill effects). It is estimated that up to 70% of infection is asymptomatic and that about 2/3 of the world population are infected by the bacterium, making it the most widespread infection in the world. Actual infection rates vary from nation to nation - the West (Western Europe, North America, Australasia) having rates around 25% and much higher in the Third World. 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''.^[14] There are already many metronidazole resistant strains in Europe, the United States, and developing countries.
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 widely believed that in the absence of treatment, ''H. pylori'' infection—once established in its gastric niche—persists for life. In the elderly, however, it is likely infection can disappear as the stomach's mucosa becomes increasingly atrophic and inhospitable to colonization. The proportion of acute infections that persist is not known, but several studies that followed the natural history in populations have reported apparent spontaneous elimination. Dynamics of ''Helicobacter pylori'' infection in a US-Mexico cohort during the first two years of life., Goodman K, O'rourke K, Day R, Wang C, Nurgalieva Z, Phillips C, Aragaki C, Campos A, de la Rosa J, , , Int J Epidemiol, 2005 The role of epidemiology in understanding the health effects of ''Helicobacter pylori''., Goodman K, Cockburn M, , , Epidemiology, 2001

Treatment of infection

In peptic ulcer patients where infection is detected, the normal procedure is eradicating ''H. pylori'' to allow the ulcer to heal. The standard first-line therapy is a one week ''triple therapy''. The Sydney gastroenterolgist Thomas Borody invented the first triple therapy in 1987. Today, the standard triple therapy is amoxicillin, clarithromycin and a proton pump inhibitor such as omeprazole. Variations of the triple therapy have been developed over the years, such as using a different proton pump inhibitor, or using metronidazole instead of amoxicillin in those allergic to penicillin. Current Concepts in the Management of Helicobacter pylori Infection European Helicobacter Pylori Study Group Such a therapy has revolutionised the treatment of peptic 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.^[15][16]
A meta-analysis of randomized controlled trials suggests that supplementation with probiotics can improve eradication rates and reduce adverse events.^[17]
Unfortunately, an increasing number of infected individuals are found to harbour antibiotic-resistant bacteria. This results in initial treatment failure and requires additional rounds of antibiotic therapy or alternative strategies such as a quadruple therapy. Bismuth compounds are also effective in combination with the above drugs. For the treatment of clarithromycin-resistant strains of ''H. pylori'' the use of levofloxacin as part of the therapy has been suggested.
Some studies show that consumption of broccoli sprouts can be effective at inhibiting ''H. pylori'' growth^[18] with sulforaphane being at least one of the active agents^[19].
Some studies show that mastic gum can destroy ''H. pylori'' ''in vitro'', but studies done ''in vivo'' have shown it to be ineffective.^[20]
A study done on Mongolian gerbils indicates that green tea extract can suppress ''H. pylori'' growth.^[21] Another study done in South Korea suggests that an acidic polysaccharide found in green tea is significantly effective in preventing adhesion of ''H. pylori'' to human cultures of epithelial cells. Inhibition of pathogenic bacterial adhesion by acidic polysaccharide from green tea (Camellia sinensis), Lee J, Shim J, Lee J, Kim J, Yang I, Chung M, Kim K, , , J Agric Food Chem, 2006
As explained below, some authors suggest that some strains of ''H. pylori'' 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.

''Helicobacter'' and cancer

While the incidence of ''H. pylori'' infection in humans is decreasing in developing countries, presumably because of improving sanitation and increasing use of antibiotics, in the United States the incidence of gastric cancer has decreased by 80 percent from 1900 to 2000. This apparent correlation is consistent with an epidemiological link between ''H. pylori'' and cancer. Specifically, both 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). Despite these associations, a direct causal relationship has not been demonstrated. Nonetheless, among bacteria suspected to cause cancer, ''H. pylori'' is the leading contender.
As the incidence of gastric cancer has decreased, the incidences of gastroesophageal reflux disease and esophageal cancer have increased dramatically. 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 gastric acid into the esophagus. While some favorable evidence has been accumulated, as of 2005 the theory is not universally accepted.
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"^[22] 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.

Genome studies of different strains

Several strains are known, and the genomes of two have been completely sequenced.^[23] 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

★ Gastritis

★ Peptic ulcer

★ Stomach

Notes

1. Chapter 23: ''Campylobacter'' and ''Helicobacter'' from ''Medical Microbiology'', 4th ed., by Samuel Baron (editor), 1996
2. Discovery by Jaworski of Helicobacter pylori and its pathogenetic role in peptic ulcer, gastritis and gastric cancer, Konturek JW, , , J Physiol Pharmacol., 2003 Dec
3. Barry Marshall biography, The Tall Poppy Campaign. Accessed 9 September 2006.
4. Unidentified curved bacillus on gastric epithelium in active chronic gastritis, Marshall BJ, , , Lancet, 1983
5. Unidentified curved bacilli in the stomach patients with gastritis and peptic ulceration, Marshall BJ, Warren JR, , , Lancet, 1984
6. Helicobacter pylori in peptic ulcer disease
7. Helicobacter pylori duodenal colonization is a strong risk factor for the development of duodenal ulcer., Pietroiusti A, Luzzi I, Gomez MJ, Magrini A, Bergamaschi A, Forlini A, Galante A., , , , 2005
8. Helicobacter pylori infection induces duodenitis and superficial duodenal ulcer in Mongolian gerbils
9. 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".
10. Jonathan W. Olson and Robert J. Maier. Molecular Hydrogen as an energy source for Helicobacter pylori. ''Science'' 298.5599 (Nov 29, 2002): pp.1788–1790. PMID 12459589
11. Biofilm formation by Helicobacter pylori., Stark RM, Gerwig GJ, Pitman RS, Potts LF, Williams NA, Greenman J, Weinzweig IP, Hirst TR, Millar MR, , , , 1999
12. Coccoid forms of Helicobacter pylori in the human stomach., Chan WY, Hui PK, Leung KM, Chow J, Kwok F, Ng CS, , , , 1994
13.
14. H pylori antibiotic resistance: prevalence, importance, and advances in testing
15. Cure of duodenal ulcer associated with eradication of Helicobacter pylori, Rauws EA, Tytgat GN, , , Lancet, 1990
16. Effect of triple therapy (antibiotics plus bismuth) on duodenal ulcer healing. A randomized controlled trial, Graham DY, Lew GM, Evans DG, Evans DJ, Klein PD, , , Ann. Intern. Med., 1991
17. Meta-analysis: the effect of supplementation with probiotics on eradication rates and adverse events during Helicobacter pylori eradication therapy, Tong JL, Ran ZH, Shen J, Zhang CX, Xiao SD, , , Aliment. Pharmacol. Ther., 2007 ACP Journal Club
18. Oral broccoli sprouts for the treatment of ''Helicobacter pylori'' infection: a preliminary report, Galan MV, Kishan AA, Silverman AL, , , Dig Dis Sci., 2004
19. Sulforaphane inhibits extracellular, intracellular, and antibiotic-resistant strains of Helicobacter pylori and prevents benzo[a]pyrene-induced stomach tumors., , , , , 2002
20. PubMed search for "gum mastic" and "H. pylori", accessed 9 September 2006.
21. Suppression of Helicobacter pylori-induced gastritis by green tea extract in Mongolian gerbils., Matsubara S, Shibata H, Ishikawa F, Yokokura T, Takahashi M, Sugimura T, Wakabayashi K., , , , 2003
22. Review article: inflammation-related promotion of gastrointestinal carcinogenesis - a perigenetic pathway, Tsuji S, Kawai N, Tsujii M, Kawano S, Hori M, , , Aliment Pharmacol Ther, 2003
23. 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.

References

★ ''Helicobacter pylori'' and peptic ulcer

★ Clinical review: ABC of the upper gastrointestinal tract. Epidemiology and diagnosis of ''Helicobacter pylori'' infection, Logan, Robert P H; Walker, Marjorie M, , , BMJ, 20 October 2001

External links

★ 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'' 2006 Helicobacter journal Supplement Oct 2006 - Free content

★
★ 1994–2005 back issues

★ 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''

★ ''H. pylori'' Picture Book

★ List of species in the genus ''Helicobacter''