Abstract
Persistent infection with Helicobacter pylori occurs in a large percentage of the population, particularly in countries with low socioeconomic status. Such infection nearly always produces chronic gastric inflammation, although in most individuals it is clinically silent and only a minority of infected persons develop H. pylori-induced peptic ulcers. In this review, the hypothesis that diversity among H. pylori strains is at least partly responsible for the observed variability in the outcome of infection is explored. To date, four phenotypes that vary among H. pylori strains have been identified: variations in lipopolysaccharide structure; expression of the cagA -encoded product; production of a vacuolating cytotoxin, and enhanced activation of neutrophils. These phenotypes are associated with one another, with enhanced tissue inflammation, and with peptic ulceration, suggesting that H. pylori strain characteristics have an important influence on the clinical outcome of H. pylori infection.