| Scope and method of study. This research was undertaken to better understand the relationship of outer membrane proteins (OMPs) of Pasteurella haemolytica to immunity against bovine pneumonic pasteurellosis and to evaluate their potential as vaccine components. Two methods of obtaining outer membrane proteins, Sarkosyl extraction and sucrose gradient centrifugation, were compared. Outer membrane proteins of P. haemolytica serovars 1-15 were compared by SDS-PAGE to identify possible cross-protective immunogens. Surface OMPs were identified by labeling whole bacterial cells with {dollar}sp{lcub}125{rcub}{dollar}I. The ability of OMPs to enhance resistance against pneumonic pasteurellosis and determination of serovar cross-protection was evaluated by vaccinating cattle with OMP-enriched reactions of serovar A1, with a similar serovar (A6), and with a dissimilar serovar (A9) followed by challenge with P. haemolytica A1. The immune response to major OMPs was correlated with resistance against experimental bovine pneumonic pasteurellosis by immunoblot procedures for the purpose of identifying OMPs that induce antibodies correlated with resistance.; Findings and conclusions. The Sarkosyl method of obtaining OMPs from P. haemolytica A1 was more efficient and less laborious than separating membranes by sucrose gradient centrifugation. Serovars 1, 2, 5, 6, 7, 8, 11, and 12 which are A biovars had similar OMP profiles characterized by major OMPS of 30.5 and 43 kDa. Serovars 9, 13, and 14 which are A biovars had profiles more consistent with the T biovars. A 43 kDa protein was present in all serovars although concentration was greatest in the A biovars. Surface-exposed proteins identified by {dollar}sp{lcub}125{rcub}{dollar}I-labeling were 94, 84, 53.5, 49, 43, 41, 29.5, and 16 kDa. Sarkosyl-derived OMP preparations induced a protective response in calves against intrathoracic challenge with the homologous serovar. OMP fractions from heterologous serovars, A6 and A9, induced partial protection that was associated with their respective similarities to A1 in OMP profiles by SDS-PAGE. Immunoblotting data revealed that antibodies to OMPs of 82-84.5, 63, 50.5, 45.5, 37, 29 and 16.5 kDa were significantly correlated with resistance to experimental challenge. OMPs that are surface-exposed and correlate positively to resistance are 84.5, 50.5, 45.5, 29, and 16.5 kDa. These latter OMPs are worthy of continued study as potential components of efficacious vaccines for bovine pneumonic pasteurellosis. |
