Research paperDeletion of the vacJ gene affects the biology and virulence in Haemophilus parasuis serovar 5

•Haemophilus parasuis VacJ lipoprotein was implicated in maintaining the outer membrane integrity.•Deleting the vacJ gene increased susceptibility to stress conditions, several antibiotics and complement-dependent killing.•Deleting the vacJ gene decreased ability to biofilm formation, adherence to and invasion of PK-15 cells.•Deleting the vacJ gene attenuated the pathogenicity of H. parasuis in mice.

Haemophilus parasuis is an important pathogen causing severe infections in pigs. However, the specific bacterial factors that participate in pathogenic process are poorly understood. VacJ protein is a recently discovered outer membrane lipoprotein that relates to virulence in several pathogens. To characterize the function of the vacJ gene in H. parasuis virulent strain HS49, a vacJ gene-deletion mutant ΔvacJ and its complemented strain were constructed. Our findings supported that VacJ is essential for maintenance of cellular integrity and stress tolerance of H. parasuis, by the demonstrations that the ΔvacJ mutant showed morphological change, increased NPN fluorescence and, and decreased resistance to SDS-EDTA, osmotic and oxidation pressure. The increased susceptibility to several antibiotics in the ΔvacJ mutant further suggested that the stability of the outer membrane was impaired as a result of the mutation in the vacJ gene. Compared to the wild-type strain, the ΔvacJ mutant strain caused a decreased survival ratio from the serum and complement killing, and exhibited a significant decrease ability to adhere to and invade PK-15 cell. In addition, the ΔvacJ mutant showed reduced biofilm formation compared to the wild-type strain. Furthermore, the ΔvacJ was attenuated in a murine (Balb/C) model of infection and its LD50 value was approximately fifteen-fold higher than that of the wild-type or complementation strain. The data obtained in this study indicate that vacJ plays an essential role in maintaining outer membrane integrity, stress tolerance, biofilm formation, serum resistance, and adherence to and invasion of host cells related to H. parasuis and further suggest a putative role of VacJ lipoprotein in virulence regulation.