The Microbiology and Epidemiology ofHelicobacter pyloriInfection

Publisher Website
Google Scholar
Abstract
Helicobacter pylori is part of a genus of specialized bacteria that have adapted to the ecological niche provided by gastric mucus. H. pylori has exploited the human niche, while further species of Helicobacter have inhabited the gastric mucosa of other animals. The preferred habitat of H. pylori is the gastric antrum. In humans with normal gastric function, the organism is mainly restricted to the antral surface, where a number of specialized traits allow it to flourish, while causing minimal harm to its host. These include a characteristic motility that allows it to swim rapidly through viscous mucus, and the ability to manufacture large amounts of the enzyme urease. This enzyme breaks down endogenous urea to form ammonia, which protects the bacterium from gastric acidity. Specific adhesins bind a number of the bacteria to the gastric surface, some swim freely in the mucus, and others possibly endocytose into the epithelial cells. It is probably these inaccessible colonization sites that make the organism so difficult to eradicate. In some patients, the normally harmless balance between host and bacterium is disturbed, resulting in peptic ulceration. Modifications to the mucus or epithelial surface in the proximal duodenum, towards the gastric phenotype, make the tissue more susceptible to H. pylori infection of the duodenum by spread of organisms from the antrum. Gastric acid output becomes further increased and the duodenal mucosa is rendered more susceptible to acid attack, leading to peptic ulceration. In other situations, the level of inflammation is enhanced and immunopathology results, followed in the longer term in some cases by atrophy and gastric cancer. H. pylori is a well-adapted, successful parasite and is one of the most common chronic infections known. The organism is acquired via ingestion. Transmission under normal circumstances is difficult and is considered to be oral-oral. The period of greatest susceptibility to infection is probably during childhood. Transmission is facilitated by a high density of living and correlates with a lower socioeconomic status. The children of persons harbouring H. pylori have a greater chance of infection. Prevalence in developing countries can be as high as 75% by the age of 2 years, but as the living conditions in a society improve, so the number of persons infected with H. pylori declines. As with any microbe emerging as an important pathogen, the principal challenge is to understand the ecology and epidemiology of infection in order to be better able to develop rational management strategies.