1 Bacteriology of Helicobacter pylori

Abstract

The discovery and first isolation of H. pylori in pure culture from gastric biopsies in 1982 provided the basis for a completely new area of microbiology. Since then, H. pylori has been an intensively pursued topic worldwide, and extensive data have been acquired on all aspects of its basic microbiology, both at the conventional phenotypic level and at the molecular level. H. pylori is a remarkable microorganism because of its ability to readily colonize a major proportion of human population worldwide and to persist successfully for long periods (probably decades) in a hostile environment. At the same time it interacts with the host immune system in such a way as to permit long-term survival. Blaser (1993) proposed a model in which both host and parasite adapt to down regulate inflammatory phenomena to promote survival. Urease production by H. pylori (an important factor in that process) is one of its most distinct features with a key role in its success as an infective agent. Another less obvious yet highly significant feature of H. pylori is the ability to achieve a high degree of interstrain diversity in genomic DNA nucleotide sequences, while maintaining overall genetic homology and phenotypic homogeneity amongst strains. The selective advantage this diversity provides the bacterium is not understood. A key objective of future microbiological studies should be to understand the population genetic structure of H. pylori. Most species of bacteria are clonal in natural population structure, yet all genomic data suggest the contrary is true for H. pylori. Furthermore, it is not clear if all strains of H. pylori are equally pathogenic, and that some subsets may possess additional pathogenicity factors that are responsible for the development of different disease pathologies. A phylogenetic framework of the genetic relationships of the clones within H. pylori would enable an examination of the total genetic diversity, with respect to ethnic or geographical population and the nature of the disease caused. A second aim would be to understand the mode of transmission of H. pylori from individual to individual. Although there is some evidence for either an oral-oral or a faecal-oral route, no reliable microbiological protocols exist for the isolation of H. pylori from non-gastric sites. There is therefore, considerable scope for the development of microbiological media and test methods for isolation from faeces and dental plaque, and possibly even food and environmental sources. To conclude, the availability of new information on the above aspects would greatly facilitate the monitoring of therapy; would enable more accurate epidemiological studies on the age of acquisition and spread of H. pylori infection; and would provide a basis for future prevention of disease by identification of individuals at high risk of infection with a particular pathogenic strain type.