Pasteurella multocida- and Pasteurella haemolytica-ghosts: new vaccine candidates

Pasteurella multocida is an important animal pathogen. Bacterial ghosts produced by the expression of phage PhiX174 lysis gene E are empty cells devoid of cytoplasmic and genomic material. Lysis of P. multocida 7A and P. haemolytica A1 carrying Pasteurella-specific lysis vectors (pSR2 and pSON2) occurred 140 min after induction of gene E expression induced by temperature upshift. The E-mediated cell lysis and killing activity was the same in both Pasteurella species and no viable cells could be detected after lysis of P. multocida and P. haemolytica. Pasteurella ghosts were used for immunization of rabbits and mice. Rabbits immunized subcutaneously with either P. multocida- or P. haemolytica-ghosts developed antibodies reacting with the immunizating strain, as well as with other Pasteurella strains. The number of proteins in whole cell protein extracts recognized by the sera constantly increased during the observation period of 51 days. In addition, dose-dependent protection against homologous challenge was observed in mice immunized with P. multocida-ghosts. Animals which received 1.15 x 10(8) ghosts and a challenge dose of up to 60 cfu (LD90), showed 100% protection. According to these results, we suggest ghosts of P. multocida and P. haemolytica as new vaccine candidates.