Genetic and immunological analyses of a 38 kDa surface-exposed lipoprotein of Pasteurella haemolytica A1.

Pasteurella haemolytica serotype A1 is the bacterial pathogen most frequently isolated from the lungs of cattle with bovine respiratory disease. As part of a study to characterize P. haemolytica antigens which are important in eliciting resistance to pneumonic pasteurellosis, we have cloned and sequenced the gene encoding a 38 kDa lipoprotein, Lpp38. The deduced amino acid sequence of Lpp38 is similar to those of the Escherichia coli polyamine transport proteins PotD (70%) and PotF (33%). P. haemolytica Lpp38 is present in both inner membrane and outer membrane fractions of the cell envelope. Susceptibility of Lpp38 to cleavage by extracellular proteases indicates that portions of the protein are surface-exposed. A protein of similar molecular mass in P. haemolytica strains from all 12 serotypes of biotype A and in an untypeable strain was detected by an anti-Lpp38 monoclonal antibody. Lpp38 is recognized by sera from calves resistant to infection after natural exposure to P. haemolytica and by sera from calves protected against infection by vaccination with P. haemolytica A1 outer membranes or with live bacteria. These data suggest a role for this protein in the development of immunity to P. haemolytica infection.