Helicobacter is a genus of Gram-negative bacteria possessing a characteristic helical shape. They were initially considered to be members of the genusCampylobacter, but in 1989, Goodwin et al. published sufficient reasons to justify the new genus nameHelicobacter. The genus Helicobacter contains about 35 species. Some species have been found living in the lining of the upper gastrointestinal tract, as well as the liver of mammals and some birds. 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 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 enzymeurease, 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 such as penicillin, are microaerophiliccapnophiles, and are fast-moving with their flagella.
Molecular signatures
Comparative genomic analysis has led to the identification of 11 proteins which 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-''Helicobacter pylori'' species
Recently, new gastric and enterohepatic species have been reported. H. pylori is of primary importance for medicine, but non-H. pylori species, which naturally inhabit mammals and birds, have been detected in human clinical specimens. These encompass two 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, 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 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.
''Helicobacter heilmannii sensu lato''
Helicobacter heilmannii sensu lato is a grouping of non-Helicobacter pylorihelicobacterbacteria 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 extrnodal marginal B cell lymphoma of the stomach in humans and animals. Most clinical studies have not identified the exact species of Helicobacter heilmanii associated with these diseases and therefore 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 Helicobacter 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 Helicobacter 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 Helicobacter heilmannii sensu lato species. The H. heilmanni s.l.-associated human diseases appear to be acquired from pets and farm animals and are therefore considered to be zoonotic diseases.
