''Helicobacter'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wa ...

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

possessing a characteristic helical shape. They were initially considered to be members of the genus ''

Campylobacter ''Campylobacter'' (meaning "curved bacteria") is a genus of Gram-negative bacteria. ''Campylobacter'' typically appear comma- or s-shaped, and are motile. Some ''Campylobacter'' species can infect humans, sometimes causing campylobacteriosis, ...

'', 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 GI tract contains all the major organs of the digestive system, in humans an ...

, as well as the

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it i ...

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

s and some

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

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 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 species that contains the biological type specim ...

of the genus. Some strains of this bacterium are

pathogen In biology, a pathogen ( el, πάθος, "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 g ...

ic to humans, as they are strongly associated with

peptic ulcer Peptic ulcer disease (PUD) is a break in the inner lining of the stomach, the first part of the small intestine, or sometimes the lower esophagus. An ulcer in the stomach is called a gastric ulcer, while one in the first part of the intestines ...

s, chronic

gastritis Gastritis is 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). Other possi ...

, duodenitis, and

stomach cancer Stomach cancer, also known as gastric cancer, is a cancer that develops from the lining of the stomach. Most cases of stomach cancers are gastric carcinomas, which can be divided into a number of subtypes, including gastric adenocarcinomas. Ly ...

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

acidic In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a ...

mammalian

stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...

by producing large quantities of the

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

urease Ureases (), functionally, belong to the superfamily of amidohydrolases and phosphotriesterases. Ureases are found in numerous bacteria, fungi, algae, plants, and some invertebrates, as well as in soils, as a soil enzyme. They are nickel-contai ...

, 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 bacterial infections, and antibiotic medications are widely used in the treatment and preventio ...

such as

penicillin Penicillins (P, PCN or PEN) are a group of β-lactam antibiotics originally obtained from '' Penicillium'' moulds, principally '' P. chrysogenum'' and '' P. rubens''. Most penicillins in clinical use are synthesised by P. chrysogenum usin ...

, are microaerophilic (optimal

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

concentration between 5 and 14%)

capnophiles Capnophiles are microorganisms that thrive in the presence of high concentrations of carbon dioxide (). Some capnophiles may have a metabolic requirement for carbon dioxide, while others merely compete more successfully for resources under thes ...

, and are fast-moving with their

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have fro ...

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, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ...

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 (which may be bloody if inflammation is severe), fever, abdominal distensi ...

and

ulcerative colitis Ulcerative colitis (UC) is a long-term condition that results in inflammation and ulcers of the colon and rectum. The primary symptoms of active disease are abdominal pain and diarrhea mixed with blood (hematochezia). Weight loss, fever, and ...

. 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) occurs when microbes evolve mechanisms that protect them from the effects of antimicrobials. All classes of microbes can evolve resistance. Fungi evolve antifungal resistance. Viruses evolve antiviral resistance. ...

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

''H. heilmannii sensu lato''

Helicobacter heilmannii sensu lato ''Helicobacter heilmannii sensu lato'' refers to a group of bacterial species within the '' Helicobacter'' genus. The ''Helicobacter'' genus consists of at least 40 species of spiral-shaped (also described as corkscrew-shaped) flagellated, Gr ...

'' (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 bizzozeronii'' is a species within the '' Helicobacter'' genus of Gram-negative bacteria. '' Helicobacter pylori'' is by far the best known ''Helicobacter'' species, primarily because humans infected with it may develop gastroint ...

, Helicobacter felis, Helicobacter salomonis,

Helicobacter suis ''Helicobacter suis'' (''H. suis'') is a species within the '' Helicobacter'' genus of Gram-negative bacteria. '' Helicobacter pylori'' is by far the best known ''Helicobacter'' species, primarily because humans infected with it may develop ga ...

'', 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 bacterium, virus, parasite or prion) that has jumped from a non-human (usually a vertebrate) to a ...

References

External links

Helicobacter
genomes and related information a
PATRIC
a Bioinformatics Resource Center funded b
NIAID

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

''Helicobacter'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
{{Taxonbar, from=Q134684 Conditions diagnosed by stool test Gastroenterology Gram-negative bacteria Pathogenic bacteria Campylobacterota Bacteria genera