Helicobacter

Helicobacter is a genus of Gram-negative bacteria 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.[2] The genus Helicobacter contains about 35 species.[3][4][5]

Helicobacter
Scanning electron micrograph of Helicobacter bilis bacteria
Scientific classification
Domain: Bacteria
Phylum: Campylobacterota
Class: "Campylobacteria"
Order: Campylobacterales
Family: Helicobacteraceae
Genus: Helicobacter
Goodwin et al. 1989
Species

H. acinonychis
H. ailurogastricus[1]
H. anseris
H. aurati
H. apri[1]
H. baculiformis
H. bilis
H. bizzozeronii
H. brantae
H. canadensis
H. canicola[1]
H. canis
H. cetorum
H. cholecystus
H. cinaedi
H. cynogastricus
H. equorum
H. felis
H. fennelliae
H. ganmani
H. heilmannii
H. hepaticus
H. himalayensis[1]
H. japonicus[1]
H. mesocricetorum
H. macacae
H. marmotae
H. mastomyrinus
H. mesocricetorum
H. muridarum
H. mustelae
H. pametensis
H. pullorum
H. pylori
H. rappini
H. rodentium
H. saguini[1]
H. salomonis
H. suis
H. trogontum
H. typhlonius
H. valdiviensis[1]
H. winghamensis

Some species have been found living in the lining of the upper gastrointestinal tract, as well as the liver of mammals and some birds.[6] The most widely known species of the genus is H. pylori, which infects up to 50% of the human population.[5] It also serves as the type species of the genus. Some strains of this bacterium are pathogenic to humans, as they are strongly associated with peptic ulcers, chronic gastritis, duodenitis, and stomach cancer.

Helicobacter species are able to thrive in the very acidic mammalian stomach by producing large quantities of the enzyme urease, which locally raises the pH from about 2 to a more biocompatible range of 6 to 7.[7] Bacteria belonging to this genus are usually susceptible to antibiotics such as penicillin, are microaerophilic (optimal oxygen concentration between 5 and 14%) capnophiles, and are fast-moving with their flagella.[8][9]

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.[10]

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 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 and ulcerative colitis. 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, and treatment regimens for infections and pathogenesis and possible carcinogenesis in humans should be evaluated.[3]

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,[11] duodenum ulcers,[12] stomach cancers that are not lymphomas, and extranodal marginal B cell lymphoma of the stomach in humans and animals.[11] 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 upper gastrointestinal tract 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.[11] 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.[13] The H. heilmanni s.l.-associated human diseases appear to be acquired from pets and farm animals, so are considered to be zoonotic diseases.[11]

References
  1. Parte, A.C. "Helicobacter". LPSN.
  2. 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 (4): 397–405. doi:10.1099/00207713-39-4-397.
  3. Boyanova, L, ed. (2011). Helicobacter pylori. Caister Academic Press. ISBN 978-1-904455-84-4.
  4. 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 (1): 88–103. doi:10.1099/00207713-41-1-88. PMID 1704793.
  5. Yamaoka, Y., ed. (2008). Helicobacter pylori: Molecular Genetics and Cellular Biology. Caister Academic Press. ISBN 978-1-904455-31-8. .
  6. Ryan, KJ; Ray, CG, eds. (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 0-8385-8529-9.
  7. Dunn BE, Cohen H, Blaser MJ (1 October 1997). "Helicobacter pylori". Clin Microbiol Rev. 10 (4): 720–741. doi:10.1128/cmr.10.4.720. PMC 172942. PMID 9336670.
  8. Hua JS, Zheng PY, Ho B (1999). "Species differentiation and identification in the genus of Helicobacter" (PDF). World Journal of Gastroenterology. 5 (1): 7–9. doi:10.3748/wjg.v5.i1.7. PMC 4688506. PMID 11819372. Archived from the original (PDF) on 24 December 2004.
  9. Rust; et al. (2008). "Helicobacter Flagella, Motility and Chemotaxis". Helicobacter pylori: Molecular Genetics and Cellular Biology (Yamaoka Y, ed.). Caister Academic Press. ISBN 978-1-904455-31-8. .
  10. Zakharova N.; Paster B. J.; Wesley I.; Dewhirst F. E.; Berg D. E.; Severinov K. V. (1999). "Fused and overlapping rpoB and rpoC genes in Helicobacters, Campylobacters, and related bacteria". J Bacteriol. 181 (12): 3857–3859. doi:10.1128/JB.181.12.3857-3859.1999. PMC 93870. PMID 10368167.
  11. Bento-Miranda M, Figueiredo C (December 2014). "Helicobacter heilmannii sensu lato: an overview of the infection in humans". World Journal of Gastroenterology. 20 (47): 17779–87. doi:10.3748/wjg.v20.i47.17779. PMC 4273128. PMID 25548476.
  12. Iwanczak B, Biernat M, Iwanczak F, Grabinska J, Matusiewicz K, Gosciniak G (April 2012). "The clinical aspects of Helicobacter heilmannii infection in children with dyspeptic symptoms". Journal of Physiology and Pharmacology. 63 (2): 133–6. PMID 22653899.
  13. Ménard A, Smet A (September 2019). "Review: Other Helicobacter species". Helicobacter. 24 Suppl 1: e12645. doi:10.1111/hel.12645. PMID 31486233.
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