Mutation of the cytotoxin-associated cagA gene does not affect the vacuolating cytotoxin activity of Helicobacter pylori

Helicobacter pylori now is recognized as an etiological agent in chronic superficial gastritis and peptic ulcer disease. Although only about 60% of H. pylori isolates produce an immunodominant 128-kDa antigen (CagA; cytotoxin- associated gene product), virtually all H. pylori-infected patients with duodenal ulceration develop a serologic response to the 128-kDa protein, which suggests an association of this gene with ulceration. The cloned cagA gene from H. pylori 84-183 was disrupted by insertion of a kanamycin resistance gene, and this inactivated cagA construct was introduced into H. pylori 84-183 by electrotranformation. Southern hybridization of kanamycin- resistant H. pylori transformants demonstrated that the wild-type cagA gene had been disrupted by insertion of the kanamycin cassette, and immunoblot analysis showed that the mutant strains no longer produced the 128-kDa CagA protein. Similar results were obtained when the cagA mutation was introduced by natural transformation into H. pylori 60190, a high-level toxin-producing strain. The cagA-negative H. pylori strains showed cytotoxin, urease, and phospholipase C activities, C3 binding, and adherence similar to those of the isogenic wild-type strains. These findings demonstrate that the cagA gene product does not affect the vacuolating cytotoxin activity of H. pylori.