The human pathogen Helicobacter pylori is associated with gastritis, peptic 
ulcer disease, and gastric cancer. The pathogenesis of H. pylori infection in 
vivo was studied by adapting fresh clinical isolates of bacteria to colonize the 
stomachs of mice. A gastric pathology resembling human disease was observed in 
infections with cytotoxin-producing strains but not with noncytotoxic strains. 
Oral immunization with purified H. pylori antigens protected mice from bacterial 
infection. This mouse model will allow the development of therapeutic agents and 
vaccines against H. pylori infection in humans.