Cloning and allelic exchange mutagenesis of two flagellin genes of Helicobacter felis

Helicobacter felis has been used extensively in animal model studies of gas tric Helicobacter infections. Attempts to manipulate H. felis genetically h ave, however, been unsuccessful and, consequently, little is known about th e pathogenic mechanisms of this bacterium. In common with other Helicobacte r spp., H. felis is a highly motile organism. To characterize the flagellar structures responsible for this motility, we cloned and sequenced the two flagellin-encoding genes, flaA and flaB, from H. felis. These genes encode two flagellin proteins that are expressed simultaneously under the control of putative sigma(28) and sigma(54) promoters respectively. Isogenic mutant s of H. felis in flaA and flaB were generated by electroporation-mediated a llelic disruption and replacement, showing for the first time that H. felis could be manipulated genetically. Both types of H. felis flagellin mutants exhibited truncated flagella and were poorly motile. H. felis flaA mutants were unable to colonize the gastric mucosa ina mouse infection model.