Loss of the Capsule Increases the Adherence Activity but Decreases the Virulence of Avibacterium paragallinarum.

Avibacterium paragallinarum is the causative agent of infectious coryza, an important respiratory disease of chickens. The capsule is an important virulence determinant of many pathogenic bacteria, but the function of the capsule in Av. paragallinarum is not well defined. In this study, acapsular mutants of Av. paragallinarum were constructed by inactivation of the hctA gene using the TargeTron gene knockout system. The acapsular mutants were found to have greater hemagglutination activity than did the wild-type strain. Further, acapsular mutants exhibited an increased ability to adhere to DF-1 cells and to form biofilms on abiotic surfaces. Virulence assays showed that acapsular mutants were less virulent than the wild-type strain. Taken together, these results indicated that loss of capsule increases hemagglutination and adhesion activities but decreases the virulence of Av. paragallinarum. These results could be valuable to further elucidate the function of the capsule and the mechanism of pathogenicity of Av. paragallinarum.

CpG oligodeoxynucleotides containing GACGTT motifs enhance the immune responses elicited by a goose parvovirus vaccine in ducks.

Recombinant parvovirus VP2 (rVP2) was formulated with different types of adjuvant, including aluminum adjuvant and CpG oligodeoxynucleotides (ODNs), and the immunological responses after vaccination in ducks were examined. In comparison with the control group, production of rVP2-specific antibodies, expression of cytokines in peripheral blood mononuclear cells (PBMC) stimulated by rVP2, and percentage of CD4(+)/CD8(+) cells in PBMC were significantly increased in ducks immunized with rVP2 formulated with CpG ODNs containing 3 copies of GACGTT motif. CpG ODNs with GACGTT motifs might be used to improve the efficacy of vaccines for ducks.