Immunogenicity of recombinant Mannheimia haemolytica serotype 1 outer membrane protein PlpE and augmentation of a commercial vaccine.

Mannheimia haemolytica is the major cause of severe bacterial pneumonia associated with shipping fever in cattle. The gene for M. haemolytica outer membrane protein (OMP) PlpE was cloned into the expression vector pRSETA. The cloned gene was then expressed in BL21(DE3)pLysS and the recombinant PlpE (rPlpE) was purified and used in immunological and vaccination studies. Vaccination of cattle with commercial M. haemolytica vaccines stimulated no significant (P>0.05) antibody responses to rPlpE. Recombinant PlpE in a commercial proprietary adjuvant was highly immunogenic when injected subcutaneously into cattle. Vaccination of cattle with 100 microg of rPlpE markedly enhanced resistance against experimental challenge with virulent M. haemolytica. Addition of 100 microg of rPlpE to a commercial M. haemolytica vaccine, Presponse, significantly enhanced (P<0.05) protection afforded by the vaccine against experimental challenge. Addition of rPlpE to commercial M. haemolytica vaccines could greatly enhance vaccine efficacy.