Characterization of flgK gene and FlgK protein required for H pylori colonization-from cloning to clinical relevance

Aim: To characterize the role of flgK and its protein product in H pylori colonization. Methods: The PCR cloning method identified the flg K gene. An isogenic flgK mutant was constructed by gene replacement and confirmed by Southern blot analysis and PCR analysis. The recombinant FlgK protein (r-FlgK) was purified. Electron microscopy (EM) was applied to demonstrate the flagella of H pylori. An in vitro motility test was assessed in semisolid medium. The densities of H pylori colonization with either the wild-type strain or its flgK mutant were compared among BALB/c mice with or without pre-immunization with r-FlgK. The serological responses to r-FlgK were analyzed for 70 clinical patients with different densities of H pylori colonization. Results: From a duod enal ulcer strain, the flgK gene was cloned and it contained 1821 bp, with a 95.7% identity to the published sequences. No flagella were observed under EM for the mutant strain, which had a loss of motility. H pylori density was lower in the BALB/c mice inoculated by the mutant or with pre-immunization with r-FlgK compared to unimmunized mice or mice inoculated by the wild-type strain (P < 0.05). In the H pylori-infected patients, the serological responses to r-FlgK were uniformly low in titer. Conclusion: FlgK encoded by flgK is important for flagella formation and H pylori motility. Deficiency in FlgK or an enhanced serological response to r-FlgK can interfere with H pylori colonization. FlgK of H pylori could be a novel target for vaccination.