Helicobacter pylori or H.pylori is a gram-negative, helix/spiral shaped bacterium (plural ~ bacteria). It has multiple flagella (long tail-like projection) at one end which allows it to move through the stomach and burrow deep into the stomach lining (gastric mucosa). This bacteria has in-built mechanisms to neutralize stomach acid around it and has an affinity for gastric epithelium. H.pylori is therefore almost always found living exclusively in the stomach and to some extent in the duodenum.

How does H.pylori infection work?

Pathophysiology of H.pylori

H.pylori infection of the stomach is one of the main causes of acute gastritis (stomach lining inflammation) and peptic ulcers (more often duodenal than gastric ulcers). The prevalence of H.pylori infection in adults is significantly high but most cases are asymptomatic (no symptoms). This could be due to  the absence of individual risk factors, the strain of the H.pylori involved or other unknown factors.

H.pylori burrows deep into the mucosal lining until it finds and attaches to the antigens on the surface of epithelial cells. The bacteria produces large amounts of urease, an enzyme that can break down urea in the stomach. By breaking down the urea, it produces ammonia which forms a ‘cloud’ around the bacterium. This raises the pH (acid-base level) making the immediate environment less acidic thereby protecting the bacterium from the corrosive stomach acid.

Apart from counteracting the stomach acid and exposing the underlying layers of the stomach to the acid, H.pylori can also cause localized inflammation within the stomach wall, release proteins that causes cell death, inhibit immune activity and affect the secretion of hormones from the stomach wall (gastrin and somastatin). H.pylori acts on G cells to increase the secretion of gastrin (hypergastrinemia) which will then increase the production and secretion of stomach acid (stomach acid hypersecretion).

How is H.pylori spread?

Transmission of H.pylori

H.pylori is more often spread by person-to-person contact.

The most common way it is spread is through oral-to-oral contact (stomach contents from one person’s mouth to another). Kissing or sharing food is one method of transmission especially if there is gastric refluxate or remnants of vomit in the mouth. Less frequently, saliva may be a medium of transmission. This may explain the incidence of H.pylori infection in families, between parent-child and siblings.

The other method is the fecal-to-oral (stool to mouth). This may involve contaminated food or water and could account for the very high incidence of H.pylori infection in the adult populations of developing nations (unclean water sources).


Article reviewed by Dr. Greg. Last updated on June 14, 2010