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 serotypes 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 serotypes 2 and 5 is dependent on the presence or absence of PEtn on Hep II.