SUBSTRATA MAIN PAGE|
TAXONOMY: Proteobacteria -> delta/epsilon subdivisions -> Epsilonproteobacteria -> Campylobacterales -> Helicobacteraceae -> Helicobacter -> Helicobacter pylori
Helicobacter pylori, previously Campylobacter pylori, is a gram-negative, microaerophilic bacterium found usually in the stomach. It was identified in 1982 by Australian scientists Barry Marshall and Robin Warren, who found that it was present in a person with chronic gastritis and gastric ulcers, conditions not previously believed to have a microbial cause. It is also linked to the development of duodenal ulcers and stomach cancer. However, over 80% of individuals infected with the bacterium are asymptomatic, and it may play an important role in the natural stomach ecology.More than 50% of the world's population harbor H. pylori in their upper gastrointestinal tract. Infection is more prevalent in developing countries, and incidence is decreasing in Western countries. H. pylori's helical shape (from which the genus name is derived) is thought to have evolved to penetrate the mucoid lining of the stomach. H. pylori is a helix-shaped (classified as a curved rod, not spirochaete) Gram-negative bacterium about 3 μm long with a diameter of about 0.5 μm. It is microaerophilic; that is, it requires oxygen, but at lower concentration than is found in the atmosphere. It contains a hydrogenase which can be used to obtain energy by oxidizing molecular hydrogen (H2) produced by intestinal bacteria. It produces oxidase, catalase, and urease. It is capable of forming biofilms and can convert from spiral to a possibly viable but nonculturable coccoid form, both likely to favor its survival and be factors in the epidemiology of the bacterium. H. pylori possesses five major outer membrane protein families. The largest family includes known and putative adhesins. The other four families are porins, iron transporters, flagellum-associated proteins, and proteins of unknown function. Like other typical Gram-negative bacteria, the outer membrane of H. pylori consists of phospholipids and lipopolysaccharide (LPS). The O antigen of LPS may be fucosylated and mimic Lewis blood group antigens found on the gastric epithelium. The outer membrane also contains cholesterol glucosides, which are found in few other bacteria. H. pylori has four to six lophotrichous flagella; all gastric and enterohepatic Helicobacter species are highly motile owing to flagella. The characteristic sheathed flagellar filaments of Helicobacter are composed of two copolymerized flagellins, FlaA and FlaB. To avoid the acidic environment of the interior of the stomach (lumen), H. pylori uses its flagella to burrow into the mucus lining of the stomach to reach the epithelial cells underneath, where the pH is more neutral. H. pylori is able to sense the pH gradient in the mucus and move towards the less acidic region (chemotaxis). This also keeps the bacteria from being swept away into the lumen with the bacteria’s mucus environment, which is constantly moving from its site of creation at the epithelium to its dissolution at the lumen interface. H. pylori is found in the mucus, on the inner surface of the epithelium, and occasionally inside the epithelial cells themselves. It adheres to the epithelial cells by producing adhesins, which bind to lipids and carbohydrates in the epithelial cell membrane. One such adhesion, BabA, binds to the Lewis b antigen displayed on the surface of stomach epithelial cells. Another such adhesion, SabA, binds to increased levels of sialyl-Lewis x antigen expressed on gastric mucosa.In addition to using chemotaxis to avoid areas of low pH, H. pylori also neutralizes the acid in its environment by producing large amounts of urease, which breaks down the urea present in the stomach to carbon dioxide and ammonia. The ammonia, which is basic, then neutralizes stomach acid. To explain how the treatment of Helicobacter pylori infection helps those suffering from Parkinson's disease, it has been proposed, with some experimental support, that this is because the L-DOPA supplements given to these patients are actually used by H. pylori. Identified as a constituent of the oral microbiome by Human Oral Microbiome Database.
This species has been identified as a resident in the human gastrointestinal tract based on the phylogenetic framework of its small subunit ribosomal RNA gene sequences.[PMC 4262072]
|COGEM released a comprehensive database of pathogenicity assessment of around 2575 bacterial species in 2011. The database ranks the pathogenicity of species on a scale of 1 to 4. Helicobacter pylori ranks 2 on this scale: Species that can cause diseases in humans or animals, which are
unlikely to spread in the human population and for which an adequate
prophylaxis or therapy exists|