ESSENTIAL ROLE OF HELICOBACTER-PYLORI UREASE IN GASTRIC COLONIZATION - DEFINITE PROOF USING A UREASE-NEGATIVE MUTANT CONSTRUCTED BY GENE REPLACEMENT

Objective: To investigate the involvement of urease in Helicobacter py lori colonization in the nude mouse stomach by using a genetically def ined urease-negative mutant. Methods and results: Through electroporat ion-mediated gene replacement, one of the urease genes of an H. pylori strain, CYP3401, was disrupted by insertion of a kanamycin-resistance determinant to construct a stable urease-negative mutant, HPT73. Sout hern analysis confirmed that gene replacement was achieved. The two is ogenic strains were introduced into the stomachs of nude mice, and the number of H. pylori and the histological changes in the stomachs were investigated 1 or 4 weeks after the challenge. Gastritis was present in the CPY3401-challenged stomach, from which bacteria indistinguishab le from CPY3401 were successfully recovered. In contrast, no gastritis was found in the HPT73-challenged stomach, and H. pylori was not reco vered from these stomachs. Conclusion: H. pylori urease is essential f or colonization of the nude mouse stomach.