Helicobacter

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A genus of gram-negative bacilli whose members are spiral shaped, showing corkscrewlike motility generated by multiple, usually polar flagella. Helicobacter species require low concentrations of oxygen for maximum growth and produce the enzymes oxidase, catalase, and urease.

Different species of Helicobacter are found in the stomachs of different animals: H. felis in cats and dogs, H. mustelae in the domestic ferret, H. nemestrinae in the pigtailed macaque, and H. acinonyx in captive cheetahs with gastritis. Helicobacter pylori, found in the human stomach, is extremely common. In the United States and similarly developed countries, its prevalence increases at about 1% per year of age so that the majority of adults above age 50 are infected. In less developed countries, infection rates are dramatically higher, with up to 80% of children infected.

Helicobacter pylori is present in virtually all cases of chronic gastritis, which progresses slowly (years or decades) from asymptomatic to atrophic gastritis with impaired acid secretion. Virtually all individuals with duodenal ulcers are infected with H. pylori, which colonizes sites in the duodenum. The termination of treatment for duodenal ulcers leads to a high rate of recurrence of the ulcers, but ulcer treatment plus eradication of H. pylori from the stomach usually leads to a permanent cure. A significant proportion of individuals with H. pylori-associated atrophic gastritis develop intestinal-cell metaplasia in the stomach, a condition which is known to represent a precancerous state. See also Cancer (medicine); Ulcer.

Helicobacter pylori virulence factors include its shape and its ability to rapidly move into and through the gastric mucous coating, which protects the organism from stomach acid; its surface-associated urease enzyme which neutralizes stomach acid near the organism; a cytotoxin; and a fibrillar adhesin which binds the organism to the surface of gastric epithelial cells. Helicobacter pylori can survive in large numbers in spite of antibodies which are secreted into the stomach and the host immune cell response (inflammatory response) characteristic of gastritis.

A genus of gramnegative, spiral-shaped bacteria that is pathogenic and has been isolated from the intestinal tract of mammals, including humans.

Microaerophilic, curved to spiral-shaped, gram-negative bacteria associated with gastritis and peptic ulcer disease in humans. The type species is H. pylori. It may also be involved in the etiology of gastric neoplasia.

• H. acinonys, H. canis, H. felis, H. heilmannii, H. mustelae — isolates from the stomach of cheetahs, dogs, cats, dogs and ferrets, respectively. It is likely that they may be responsible for gastric disease in these species.
• H. bilis — associated with multifocal hepatitis in mice.
• H. hepaticus — causes focal hepatic necrosis and focal, subacute, non-suppurative hepatitis, progressing to chronic hepatitis with bile duct hyperplasia and hepatocellular tumors in mice.

Helicobacter
Scanning electron micrograph of Helicobacter bacteria.
Scientific classification
Kingdom: Bacteria Phylum: Proteobacteria Class: Epsilon Proteobacteria Order: Campylobacterales Family: Helicobacteraceae Genus: Helicobacter Goodwin et al. 1989
Species
H. acinonychis H. anseris H. aurati H. bilis H. bizzozeronii H. brantae H. canadensis H. canis H. cholecystus H. cinaedi H. cynogastricus H. felis H. fennelliae H. ganmani H. hepaticus H. mesocricetorum H. marmotae H. muridarum H. mustelae H. pametensis H. pullorum H. pylori H. rappini H. rodentium H. salomonis H. trogontum H. typhlonius H. winghamensis

Helicobacter is a genus of Gram-negative bacteria possessing a characteristic helix shape. They were initially considered to be members of the Campylobacter genus, but since 1989 they have been grouped in their own genus.^[1][2]

Some species have been found living in the lining of the upper gastrointestinal tract, as well as the liver of mammals and some birds.^[3]. The most widely known species of the genus is H. pylori. Some strains of this bacterium are pathogenic to humans as it is strongly associated with peptic ulcers, chronic gastritis, duodenitis, and stomach cancer. It also serves as the type species of the genus.

Helicobacter spp. are able to thrive in the very acidic mammalian stomach by producing large quantities of the enzyme urease, which locally raises the pH from ~2 to a more biocompatible range of 6 to 7.^[4] Bacteria belonging to this genus are usually susceptible to antibiotics such as penicillin, are microaerophilic (require small amounts of oxygen), and are fast-moving with their flagella.^[5]

References

1. ^ Goodwin CS, Armstrong JA, Chilvers T, et al (1989). "Transfer of Campylobacter pylori and Campylobacter mustelae to Helicobacter gen. nov. as Helicobacter pylori comb. nov. and Helicobacter mustelae comb. nov., respectively.". Int. J. Syst. Bacteriol. 39: 397–405. 
2. ^ Vandamme P, Falsen E, Rossaq R, et al (1991). "Revision of Campylobacter, Helicobacter, and Wolinella taxonomy: emendation of generic descriptions and proposal of Arcobacter gen. nov.". Int. J. Syst. Bacteriol. 41: 88–103. 
3. ^ Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology, 4th ed., McGraw Hill. ISBN 0-8385-8529-9. 
4. ^ Dunn BE, Cohen H, Blaser MJ (1997). "Helicobacter pylori.". Clin Microbiol Rev. 10: 720–741. 
5. ^ Hua JS, Zheng PY, Ho B (1999). "Species differentiation and identification in the genus of Helicobacter.". World Journal of Gastroenterology. 5 (1): 7–9. 

Curved cells discovered in 1979 in stomach biopsied specimens Causes 90% of stomach & duodenal ulcers People with type O blood have a 1.5-2X higher rate of ulcers Produces large amounts of urease

Infection common especially in lower socioeconomic class/developing nations Humans primary reservoir Person-to-person spread via fecal-oral route Ubiquitous, no seasonal incidence

Diagnosis Microscopy/histologic exam of biopsy specimens Culture requires microaerophillic conditions, very slow Urease test (positive in as little as 2 hours) Treatment Therapy with tetracycline, metronidazole, bismuth (Peptobismol)

See also

• Helicobacter pylori

External links

• List of species in Helicobacter, with links to sequence information

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