Helicobacter pylori and Other Gastric Spirilla: Similarities and Differences

Abstract

Microbiologists interested in the microbial flora of the gastrointestinal tract have traditionally ignored the stomach. Due to the harsh environment resulting from acid secretion, conditions were considered to be hostile to permanent colonization by bacteria although it was accepted bacteria could survive passage into the lower bowel. An exception was the work of Savage (1980), who showed the gastric mucosa of rodents to be permanently colonized with acid-tolerant lactobacilli and yeasts. However, the isolation of Helicobacter pylori and its association with gastroduodenal disease has focussed interest on bacteria in the stomach and it is now clear that many animal species have similar bacteria colonizing their gastric surfaces, i.e. humans, dogs, cheetahs, cats, monkeys, ferrets, rats (Lee 1989a). One characteristic of the microbial ecology of harsh environments is so called low species diversity; that is, very low numbers of species are present at any one time (Alexander 1971). This is a consequence of the need for specialized adaptations being required to live in that site. This is certainly so in the stomach where usually one and at the most three bacterial species are found together. Thus most animals with bacteria inhabiting the gastric mucus have only one species present. In humans the species normally present is H. pylori. As more bacteria are isolated from other animal species it is important to compare their properties with H. pylori in order to be better able to identify those factors that are essential for gastric colonization and those which might be involved in the initiation of gastroduodenal disease.

This work is supported by a grant from the National and Medical Research Council of Australia