Construction of Isogenic Mutants of Helicobacter pylori Deficient in Urease Activity

Isolates of Helicobacter pylori that do not express urease activity appear to arise spontaneously in vitro [1]. Unhke changes in phenotype, the genetypic change(s) present in these spontaneous mutants cannot be easily defined. Therefore the use of spontaneous mutants, or those created by chemical mutagenesis, in studies aimed at resolving the contribution of urease to pathogenesis remains problematic. The solution to this problem would be to genetically engineer H. pylori mutants modified in a single determinant but otherwise genotypically identical to the parent strain. These isogenic mutants might then be tested in appropriate in vitro and /or in vivo models. It was with this rationale in mind that isogenic H. pylori urease-negative mutants were constructed. To achieve this goal, genetic exchange systems allowing the introduction of foreign DNA into H. pylori cells, first needed to be developed.