Helicobacter pylori

Helicobacter pylori
Electron micrograph of H. pylori possessing multiple flagella (negative staining)
Scientific classification
Domain:	Bacteria
Phylum:	Campylobacterota
Class:	"Campylobacteria"
Order:	Campylobacterales
Family:	Helicobacteraceae
Genus:	Helicobacter
Species:	H. pylori
Binomial name
Helicobacter pylori (Marshall et al. 1985) Goodwin et al., 1989
Synonyms
Campylobacter pylori Marshall et al. 1985

Helicobacter pylori, previously known as Campylobacter pylori, is a gram-negative, flagellated, helical bacterium. Mutants can have a rod or curved rod shape, and these are less effective.^[1][2] Its helical body (from which the genus name, Helicobacter, derives) is thought to have evolved in order to penetrate the mucous lining of the stomach, helped by its flagella, and thereby establish infection.^[3][2] The bacterium was first identified as the causal agent of gastric ulcers in 1983 by the Australian doctors Barry Marshall and Robin Warren.^[4][5]

Infection of the stomach with H. pylori is not the cause of illness itself; over half of the global population is infected but most are asymptomatic.^[6][7] Persistent colonization with more virulent strains can induce a number of gastric and extragastric disorders.^[8] Gastric disorders due to infection begin with gastritis, inflammation of the stomach lining.^[9] When infection is persistent the prolonged inflammation will become chronic gastritis. Initially this will be non-atrophic gastritis, but damage caused to the stomach lining can bring about the change to atrophic gastritis, and the development of ulcers both within the stomach itself or in the duodenum, the nearest part of the intestine.^[9] At this stage the risk of developing gastric cancer is high.^[10] However, the development of a duodenal ulcer has a lower risk of cancer.^[11]Helicobacter pylori is a class 1 carcinogen, and potential cancers include gastric mucosa-associated lymphoid tissue (MALT) lymphomas and gastric cancer.^[9][10] Infection with H. pylori is responsible for around 89 per cent of all gastric cancers, and is linked to the development of 5.5 per cent of all cases of cancer worldwide.^[12][13] H. pylori is the only bacterium known to cause cancer.^[14]

Extragastric complications that have been linked to H. pylori include anemia due either to iron-deficiency or vitamin B12 deficiency, diabetes mellitus, cardiovascular, and certain neurological disorders.^[15] An inverse link has also been claimed with H. pylori having a positive protective effect on many disorders including asthma, esophageal cancer, IBD (including GERD and Crohn's disease) and other disorders.^[15]

Some studies suggest that H. pylori plays an important role in the natural stomach ecology by influencing the type of bacteria that colonize the gastrointestinal tract.^[16][17] Other studies suggest that non-pathogenic strains of H. pylori may beneficially normalize stomach acid secretion, and regulate appetite.^[18]

In 2023, it was estimated that about two-thirds of the world's population were infected with H. pylori, being more common in developing countries.^[19] The prevalence has declined in many countries due to eradication treatments with antibiotics and proton-pump inhibitors, and with increased standards of living.^[20][21]