Abstract:[Objective] To study the role of capsule polysaccharide in pathogenesis of extraintesinal pathogenic Escherichia coli (ExPEC). [Methods] By using λ Red recombination system, we generated the capsular polysaccharide transport associated genes kpsE and kpsD double knockout mutants E058ΔkpsED and U17ΔkpsED. We then compared and analyzed the characteristics of the mutant strains and wild-type strains. [Results] The growth curves in Luria Bertani showed that the deletion of kpsED did not affect growth kinetics of the mutants. The abilities of resistance to serum and killing by chicken macrophages were significantly impaired. LD50 results showed that the double mutants completely abolished the virulence, whereas the complementation strains restored the virulence to resemble that of wild-type strains, and the colonization and coinfection model demonstrated that the deletion of kpsED led to attenuation of virulence, because the double mutant showed significantly decreased colonization compared with the wild-type strains in all organs tested in chickens. [Conclusion] These results indicated that the virulence factors encoded by capsule genes were important for the pathogenesis of ExPEC.
