Expression and immunoprotective property of a 39-kDa PlpB protein of Pasteurella multocida.

Pasteurella multocida is a Gram-negative bacterium known to infect a wide range of domestic and wild animals. The increasing incidence of P. multocida isolated from cases of fowl cholera and hemorrhagic septicemia has led to a renewed interest in this pathogen as well as in the development of vaccines. In this study, PCR primers were designed to amplify the fragment of plpB gene from P. multocida FC-Pakchong (A:1). The purified PCR product of plpB gene consisting of 831 base pairs was inserted into the pGEX-5X-1 plasmid, which expressed the GST protein, and then transformed into E. coli. The purified fusion GST-PlpB protein showed a major band of about 63 kDa on SDS-PAGE gel. After enzyme cleavage, the recombinant PlpB protein appeared at the estimated size of 36 kDa. The recombinant GST-PlpB protein was tested for the toxicity in vivo. The results showed no toxicity in mice at the highest tested concentration of the protein. Moreover, the immunoprotective property of the recombinant GST-PlpB protein was determined in mice after subcutaneous immunization and challenge with an approximate dose of 50-100 LD(50) of P. multocida serotype A:1 and A:3,4. It was demonstrated that this subunit vaccine provided 20-30% survival rate after subcutaneous immunization and challenge with an approximate dose of 50-100 LD(50) of P. multocida serotype A:1 and A:3,4 whereas all of the non-immunized mice died from P. multocida infection. In conclusion, our data indicated that the PlpB protein may not be an appropriate target as a candidate subunit vaccine for P. multocida infection.