ABSTRACT
Mannheimia haemolytica outer membrane protein PlpE, a major immunogenic outer membrane lipoprotein has identical sequences in serotypes 1 (S1) and S6. Recombinant outer membrane lipoprotein PlpE (rPLpE) from M. haemolytica S1 was added to commercial M. haemolytica S1 vaccines to determine if it would enhance vaccine-induced immunity against heterotypic M. haemolytica S6 challenge. Serum antibody responses to M. haemolytica whole cells, leukotoxin and rPlpE were measured. Experiment 1 consisted of four vaccine groups: controls, 100 microg rPlpE, M. haemolytica Bacterin-Toxoid (One Shot) and M. haemolytica Bacterin-Toxoid + 100 microg rPlpE. Vaccines were given on day 0. On day 21, calves were challenged transthoracically with M. haemolytica S6. Lung lesion scores and percentage lesion reduction were 6.3 +/- 2.0 for controls, 3.6 +/- 2.4 for rPlpE vaccinates (42.9% reduction), 3.4 +/- 1.5 for One Shot-vaccinates (46.0% reduction), and 2.4 +/- 1.4 for One Shot/rPlpE vaccinates (61.9% reduction). Experiment 2 consisted of four vaccine groups: controls, 100 microg rPlpE, M. haemolytica toxoid (Presponse), and M. haemolytica toxoid+100 microg rPlpE. On day 28, calves were challenged transthoracically with M. haemolytica S6. Lung lesion scores and percentage lesion reduction were 8.1 +/- 2.2 for controls, 4.4 +/- 4.7 for the rPlpE vaccinates (45.7% reduction), 4.8 +/- 2.2 for Presponse-vaccinates (40.7% reduction), and 2.0 +/- 1.2 for Presponse/rPlpE vaccinates (75.3% reduction). These results indicate that addition of rPlpE from M. haemolytica S1 can enhance commercial M. haemolytica vaccine-induced resistance against experimental challenge with M. haemolytica S6.
