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 i solates of H. pylori produce a potent vacuolating cytotoxin and a cyto toxin-associated protein with a molecular weight of 128000 (CagA). A m olecular genetic analysis of cytotoxin-positive and -negative strains was performed to clarify the effects of this cytotoxin in H. pylori vi rulence. Methods: We used the polymerase chain reaction and molecular cloning to obtain the gene coding for the cytotoxin. Cytotoxin-positiv e and -negative strains of H. pylori were analysed by DNA hybridizatio n and the use of antisera raised against the recombinant cytotoxin. Re sults: We cloned the entire gene coding for the cytotoxin and raised a ntisera 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, a lthough cagA gene sequences were present in the genome. Conclusions: A lthough the cagA gene was absent in cytotoxin-negative H. pylori strai ns, the cytotoxin gene was present, but not expressed, suggesting that the cagA gene may regulate cytotoxicity.