Structural and genetic basis for the serological differentiation of Pasteurella multocida Heddleston Serotypes 2 and 5

Pasteurella multocida is classified into 16 serotypes according to the Heddleston typing scheme. As part of a comprehensive study to define the structural and genetic basis of this scheme, we have determined the structure of the lipopolysaccharide (LPS) produced by P. multocida strains M1404 (B:2) and P1702 (E:5); the type strains for serotype 2 and 5 respectively. The only difference between the LPS structures made by these two strains was the absence of a phosphoethanolamine (PEtn) moiety at the 3 position of the second heptose (Hep-II) in M1404. Analysis of the lpt-3 gene, required for the addition of this PEtn residue, revealed that the gene was intact in P1702 but contained a nonsense mutation in M1404. Expression of an intact copy of lpt-3 in M1404 resulted in the attachment of a PEtn residue to the 3 position of the Hep-II residue, generating an LPS structure identical to that produced by P1702. We identified and characterized each of the glycosyltransferase genes required for assembly of the serotype 2 and 5 LPS outer core. Monoclonal antibodies raised against serotype 2 LPS recognized the serotype 2,5-specific outer core LPS structure, but recognition of this structure was inhibited by the PEtn residue on Hep-II. These data indicate that the serological classification of strains into Heddleston serotype 2 and 5 is dependent on the presence or absence of PEtn on Hep-II.