Serum resistance in Haemophilus parasuis SC096 strain requires outer membrane protein P2 expression

Haemophilus parasuis outer membrane protein P2 (OmpP2), the most abundant protein in the outer membrane, has been identified as an antigenic protein and a potential virulence factor. To study the precise function of OmpP2, an ompP2-deficient mutant (?ompP2) of a H. parasuis serovar 4 clinical strain SC096 was constructed by a modified natural transformation system. Compared with the wild-type SC096 strain, the ?ompP2 mutant showed a pronounced growth defect and exhibited significantly greater sensitivity to the bactericidal action of porcine and rabbit sera, whereas the complemented strain could restore the growth and serum resistance phenotypes. The results indicated that H. parasuis OmpP2 from SC096 strain is an important surface protein involved in serum resistance.