Biological properties and pathogenicity factors of Helicobacter pylori

The unexpected discovery of Helicobacter pylori (H. pylori) has revolutionised the history of microbiology as well as of gastroenterology in the last 30 years, with an invaluable benefit for millions of persons worldwide. The confirmation that this Gram-negative spiral bacterium could live in the stomach has rendered out-of-date the concept of inhospitality of micro-organisms in the gastric environment, after a long history of unheard reports on the presence of spiral bacteria in the stomach. The pathogenicity of H. pylori depends on its ability to colonize as well as the capability to survive in the harsh gastric environment. This is possible by a coevolution between the pathogen itself and the host. Any perturbation of this equilibrium disrupts the host-pathogen interaction, promoting the pathological effects. H. pylori has a wide range of pathogenicity factors, in particular cytotoxins, enzymes of aggression, and factors providing protection against human defense systems. The most well-characterized cytotoxins contributing to epithelial cell damage are the vacuolating cytotoxin A (VacA) and the cytotoxin-associated gene A (CagA). Only detailed knowledge of the microbiology and genomics of H. pylori infection will allow a vaccine to be produced. Today, we know that H. pylori induces strong humoral and cellular immune responses, but these are incapable of eliminating the bacterium, raising doubts about the possibility of developing an effective vaccine easily. This review highlights microbiological findings concerning H. pylori infection, focusing on colonization, survival and pathogenicity.