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.

Genome studies of different strains

Several strains are known, and the genomes of two have been completely sequenced. The Pylori Gene website allows easy access to genome information for the H. pylori 26695 and H. pylori J99 strains. The genome consists of 1.7 million base pairs, with some 1550 genes. The two sequenced strains show large genetic differences; with up to 6% of the nucleotides differing.

Related Topics:
Genome - Sequenced

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Study of the H. pylori genome is centered on attempts to understand pathogenesis, the ability of this organism to cause disease. There are 62 genes in the "pathogenesis" category of the genome database. Both sequenced strains have an approximately 40 kb long Cag pathogenicity island (a common gene sequence believed responsible for pathogenesis) that contains over 40 genes. This pathogenicity island is usually absent from H. pylori strains isolated from humans who are carriers of H. pylori but remain asymptomatic.

Related Topics:
Pathogenesis - Pathogenicity island

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The cagA gene codes for one of the major H. pylori virulence proteins. Bacterial strains that have the cagA gene are associated with an ability to cause severe ulcers. The cagA gene codes for a relatively long (1186 amino acid) protein. The CagA protein is transported into human cells where it may disrupt the normal functioning of the cytoskeleton. The Cag pathogenicity island has about 30 genes that code for a complex type IV secretion system. After attachment of H.pylori to stomach epithelial cells the CagA protein is injected into the epithelial cells by the type IV secretion system. The CagA protein is phosphorylated on tyrosine residues by a host cell membrane-associated tyrosine kinase. Pathogenic strains of H. pylori have been shown to activate the epidermal growth factor receptor (EGFR), a membrane protein with a tyrosine kinase domain. Activation of the EGFR by H. pylori is associated with altered signal transduction and gene expression in host epithelial cells that may contribute to pathogenesis. It has also been suggested that a c-terminal region of the CagA protein (amino acids 873-1002) can regulate host cell gene transcription independent of protein tyrosine phosphorylation. It is thought, due to cagA's low GC content relative to the rest of the helicobacter genome, that the gene was acquired by horizontal transfer from another cagA+ bacterial species.

Related Topics:
Virulence - Amino acid - Cytoskeleton - Type IV secretion system - Phosphorylated - Tyrosine residues - Tyrosine kinase - Signal transduction - Gene expression - C-terminal

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Each human population has a characteristic distribution of H. pylori strains that typically infect members of that population. This allows researchers to use H. pylori to study human migration patterns. It could be established that H. pylori in Amazon Indians has East Asian rather than European origins, suggesting that it arrived with the original immigrants at least 11,000 years ago.

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