Helicobacter pylori

Helicobacter pylori is a Eubacterium that infects the mucus lining of the human stomach. Many peptic ulcers and some types of gastritis are caused by H. pylori infection, although most humans who are infected will never develop symptoms. This bacterium lives in the human stomach exclusively and is the only known organism that can thrive in that highly acidic environment. It is helix-shaped (hence the name helicobacter) and can literally screw itself into the stomach lining to colonize.

Structure of the bacterium

H. pylori is a spiral-shaped gram-negative bacterium, about 3 micrometres long with a diameter of about 0.5 micrometre. It has 4-6 flagella. It is microaerophilic, i.e. it requires oxygen but at lower levels than those contained in the atmosphere. It uses hydrogen methanogenesis as an energy source.

Related Topics:
Gram-negative - 3 micrometres - Flagella - Microaerophilic - Oxygen - Atmosphere - Hydrogen - Methanogenesis

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Under conditions of environmental stress, Helicobacter will convert from a spiral to a coccoid form. This coccoid form of the organism has not been cultured, but has been found in the water supply in the US and is thought to be involved in the epidemiology of the bacterium. The coccoid form has also been found to be able to adhere to gastric epithelial cells in vitro.

Related Topics:
Coccoid - In vitro

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With its flagella and its spiral shape, the bacterium drills into the mucus layer of the stomach, and then can either be found suspended in the gastric mucosa or attached to epithelial cells. It excretes the enzyme urease, which converts urea into ammonia and bicarbonate. The release of ammonia is beneficial to the bacterium since it partially neutralizes the very acidic environment of the stomach (whose very purpose is to kill bacteria). Ammonia is, however, toxic to the epithelial cells, and with other products of H. pylori, including protease, catalase, and phospholipases, causes damage to those cells.

Related Topics:
Epithelial cells - Enzyme - Urease - Urea - Ammonia - Bicarbonate - Protease - Catalase - Phospholipase

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A recent finding is that some strains of the bacteria have a particular mechanism for "injecting" the inflammatory agent peptidoglycan from their own cell wall into epithelial stomach cells. (See below for "cagA pathogenicity island" in the section "Genome studies of different strains".) It remains unknown how this mechanism is advantageous to the bacterium. (Viala et al. 2004)

Related Topics:
Inflammatory - Peptidoglycan - Cell wall

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