[Construction and characterization of an hcp mutant of swine Bordetella bronchiseptica].

Objective: We constructed Bordetella bronchiseptica QH0814 hcp mutant to characterize its pathogenicity.[Methods] Through the homologous recombination mediated by a suicide plasmid pRE112, we acquired the mutant QH0814Δhcp successfully. Then, we evaluated the growth condition, the ability of adhesion and invasion, the median lethal dose (LD50) and the infection capacity. Methods: Through the homologous recombination mediated by a suicide plasmid pRE112, we acquired the mutant QH0814Δhcp successfully. Then, we evaluated the growth condition, the ability of adhesion and invasion, the median lethal dose (LD50) and the infection capacity. Results: There was no significant variation of the growth rate between the mutant and the parental strain. Compared with the parental strain, the adherence ability of the mutant did not change remarkably. However, the invasion ability decreased significantly. Mice lethal test showed that the LD50 of the mutant was higher than that of the parental strain. Correspondingly, the bacterial colonization of the mutant in mice blood, lung and liver was much less than that of the parental strain. Conclusion: The knocking-out of the hcp gene had no influence on bacterial growth, but it could attenuate significantly the invasion and colonization of the bacterium. Therefore, the gene may play a role in the pathogenesis of Bordetella bronchiseptica.