Molecular analysis of the Helicobacter pylori cytotoxin gene

Objective: To assess the contribution of the vacuolating cytotoxin to Helicobacter pylori virulence. Design: Approximately 50% of clinical isolates of H. pylori produce a potent vacuolating cytotoxin and a cytotoxin-associated protein with a molecular weight of 128 000 (CagA). A molecular genetic analysis of cytotoxin-positive and -negative strains was performed to clarify the effects of this cytotoxin in H. pylori virulence. Methods: We used the polymerase chain reaction and molecular cloning to obtain the gene coding for the cytotoxin. Cytotoxin-positive and -negative strains of H. pylori were analysed by DNA hybridization and the use of antisera raised against the recombinant cytotoxin. Results: We cloned the entire gene coding for the cytotoxin and raised antisera against the gene product. This gene proved to be unrelated to the gene coding for the cytotoxin-associated protein (cagA gene). The protein was not produced by cytotoxin-negative strains of H. pylori, although cagA gene sequences were present in the genome. Conclusions: Although the cagA gene was absent in cytotoxin-negative H. pylori strains, the cytotoxin gene was present, but not expressed, suggesting that the cagA gene may regulate cytotoxicity