''Helicobacter'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

possessing a characteristic helical shape. They were initially considered to be members of the genus '' Campylobacter'', but in 1989, Goodwin ''et al.'' published sufficient reasons to justify the new genus name ''Helicobacter''. The genus ''Helicobacter'' contains about 35 species. Some species have been found living in the lining of the

upper gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. ...

, as well as the

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s and some

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

s. The most widely known species of the genus is '' H. pylori'', which infects up to 50% of the human population. It also serves as the

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

of the genus. Some strains of this bacterium are

pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...

ic to humans, as they are strongly associated with

peptic ulcer Peptic ulcer disease is when the inner part of the stomach's gastric mucosa (lining of the stomach), the first part of the small intestine, or sometimes the lower esophagus, gets damaged. An ulcer in the stomach is called a gastric ulcer, while ...

s, chronic

gastritis Gastritis is the inflammation of the lining of the stomach. It may occur as a short episode or may be of a long duration. There may be no symptoms but, when symptoms are present, the most common is upper abdominal pain (see dyspepsia). Othe ...

, duodenitis, and

stomach cancer Stomach cancer, also known as gastric cancer, is a malignant tumor of the stomach. It is a cancer that develops in the Gastric mucosa, lining of the stomach. Most cases of stomach cancers are gastric carcinomas, which can be divided into a numb ...

. ''Helicobacter'' species are able to thrive in the very

acidic An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen cation, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid. The first category of acids are the ...

mammalian

stomach The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...

by producing large quantities of the

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

urease Ureases (), functionally, belong to the superfamily of amidohydrolases and phosphotriesterases. Ureases are found in numerous Bacteria, Archaea, fungi, algae, plants, and some invertebrates. Ureases are nickel-containing metalloenzymes of high ...

, which locally raises the pH from about 2 to a more biocompatible range of 6 to 7. Bacteria belonging to this genus are usually susceptible to

antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy ...

such as

penicillin Penicillins (P, PCN or PEN) are a group of beta-lactam antibiotic, β-lactam antibiotics originally obtained from ''Penicillium'' Mold (fungus), moulds, principally ''Penicillium chrysogenum, P. chrysogenum'' and ''Penicillium rubens, P. ru ...

, are microaerophilic (optimal

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

concentration between 5 and 14%) capnophiles, and are fast-moving with their

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

Molecular signatures

Comparative genomic analysis has led to the identification of 11 proteins that are uniquely found in the Helicobacteraceae. Of these proteins, seven are found in all species of the family, while the remaining four are not found in any ''Helicobacter'' strains and are unique to ''Wollinella''. Additionally, a rare genetic event has led to the fusion of the '' rpoB'' and ''rpoC'' genes in this family, which is characteristic of them.

Non-''H. pylori'' species

Recently, new gastric (''H. suis'' and ''H. baculiformis'') and enterohepatic (''H. equorum'') species have been reported. ''H. pylori'' is of primary importance for medicine, but non-''H. pylori'' species, which naturally inhabit mammals (except humans) and birds, have been detected in human clinical specimens. These encompass two (gastric and enterohepatic) groups, showing different organ specificity. Importantly, some species, such as ''H. hepaticus, H. mustelae'', and probably ''H. bilis'', exhibit carcinogenic potential in animals. They harbour many

virulence Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most cases, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its abili ...

genes and may cause diseases not only in animals, but also in humans. Gastric species such as ''H. suis'' (most often)'', H. felis, H. bizzozeronii'', and ''H. salomonis'' have been associated with chronic gastritis and peptic ulcers in humans, and importantly, with higher risk for MALT lymphoma compared to ''H. pylori''. Enterohepatic species e.g., ''H. hepaticus,'' ''H. bilis'', and ''H. ganmani'', have been detected by PCR, but still are not isolated from specimens of patients with hepatobiliary diseases. Moreover, they may be associated with

Crohn's disease Crohn's disease is a type of inflammatory bowel disease (IBD) that may affect any segment of the gastrointestinal tract. Symptoms often include abdominal pain, diarrhea, fever, abdominal distension, and weight loss. Complications outside of the ...

and

ulcerative colitis Ulcerative colitis (UC) is one of the two types of inflammatory bowel disease (IBD), with the other type being Crohn's disease. It is a long-term condition that results in inflammation and ulcers of the colon and rectum. The primary sympto ...

. The significance of avian helicobacters (''H. pullorum, H. anseris'', and ''H. brantae)'' also has been evaluated extensively. ''H. cinaedi'' and ''H. canis'' can cause severe infections, mostly in immunocompromised patients with animal exposure. Briefly, the role of these species in veterinary and human medicine is increasingly recognised. Several other topics such as isolation of still uncultured species,

antibiotic resistance Antimicrobial resistance (AMR or AR) occurs when microbes evolve mechanisms that protect them from antimicrobials, which are drugs used to treat infections. This resistance affects all classes of microbes, including bacteria (antibiotic resis ...

, and treatment regimens for infections and pathogenesis and possible carcinogenesis in humans should be evaluated.

''H. heilmannii sensu lato''

'' Helicobacter heilmannii sensu lato'' (i.e. ''H. heilmanni s.l.'') is a grouping of non-''H. pylori'' ''Helicobacter'' species that take as part of their definition a similarity to ''H. pylori'' in being associated with the development of stomach inflammation, stomach ulcers, duodenum ulcers, stomach cancers that are not lymphomas, and extranodal marginal B cell lymphoma of the stomach in humans and animals. Most clinical studies have not identified the exact species of ''H. heilmanii'' associated with these diseases, so designated these species as ''H. heilmanni s.l.'' However, investigative studies have identified these species in some patients with the cited ''H. heilmanni s.l.''-associated

diseases. The ''H. heilmani species'' identified to date in the stomachs of humans with the cited upper gastrointestinal tract diseases are: '' Helicobacter bizzozeronii, Helicobacter felis, Helicobacter salomonis, Helicobacter suis'', and ''Helicobacter heilmannii s.s.'' It is important to recognize the association of ''H. heilmannii sensu lato'' with these upper gastrointestinal tract diseases, particularly extranodal marginal zone lymphoma of the stomach, because some of them have been successfully treated using antibiotic-based drug regimens directed against the instigating ''H. heilmannii sensu lato'' species. The ''H. heilmanni s.l.''-associated human diseases appear to be acquired from pets and farm animals, so are considered to be

zoonotic diseases A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (b ...

Phylogeny

The currently accepted taxonomy is based on the

List of Prokaryotic names with Standing in Nomenclature List of Prokaryotic names with Standing in Nomenclature (LPSN) is an online database that maintains information on the naming and taxonomy of prokaryotes, following the taxonomy requirements and rulings of the International Code of Nomenclatu ...

(LPSN) and

National Center for Biotechnology Information The National Center for Biotechnology Information (NCBI) is part of the National Library of Medicine (NLM), a branch of the National Institutes of Health (NIH). It is approved and funded by the government of the United States. The NCBI is lo ...

(NCBI) Species incertae sedis: * "''Ca.'' H. bovis" De Groote et al. 1999 * "''H. callitrichis''" Won et al. 2007 * "''Ca.'' H. cebus" Gueneau de Novoa et al. 2001a * "''H. higonensis''" Tomida et al. 2024 * "''H. muricola''" Won et al. 2002 * "''H. peregrinus''" Coldham et al. 2004 * "''H. suncus''" Goto et al. 1998 * "''H. tursiopsae''" Gueneau de Novoa et al. 2001b * "''H. vulpecula''" Coldham et al. 2004

References

External links