IMMUNOCHEMICAL CHARACTERIZATION OF O-POLYSACCHARIDES COMPOSING THE ALPHA-D-RHAMNOSE BACKBONE OF LIPOPOLYSACCHARIDE OF PSEUDOMONAS-SYRINGAE AND CLASSIFICATION OF BACTERIA INTO SEROGROUPS O1 AND O2 WITH MONOCLONAL-ANTIBODIES

Murine monoclonal antibodies (Mabs) reacting with Pseudomonas syringae lipopolysaccharide (LPS) O polysaccharides (OPS) composed of tetra- a nd tri-alpha-D-rhamnose repeats in the backbone [3)D-Rha(alpha 1-3)D-R ha (alpha 1-2)D-Rha(alpha 1-2)D-Rha(alpha 1] and [3)D-Rha(alpha 1-3)D- Rha(alpha 1-2)D-Rha(alpha 1] were generated and used for immunochemica l analysis and for serological classification of the bacteria, A total of 195 of 358 P. syringae strains tested representing 21 pathovars we re shown to share a common epitope, la, and were classified into serog roup O1, All strains with pathovars aptata, glycinea, japonica, phaseo licola, and pisi, most of the strains with pathovars atrofaciens and s triafaciens, and half of the strains with pathovar syringae were class ified into serotypes O1a', O1b, O1d and Old within serogroup O1, Serog roup-specific epitope la was inferred to be related to the (alpha 1-2) D-Rha(alpha 1-3) site of the OPS backbone, The serotype-specific epito pes 1b, 1c, 1d, and 1a' were inferred as relating to the immunodominan t lateral (alpha 1-3)D-Rha, (beta 1-4)D-GlcNAc, and (alpha 1-4)D-Fuc s ubstituents and backbone-located site (alpha 1-3)D-Rha(alpha 1-2), res pectively, of OPSs that share the common tetra-D-rhamnose repeats in t he backbone. A total of 7.3% of the strains studied, all with pathovar s morsprunorum and lapsa, were classified as serotypes O2a and O2d wit hin serogroup O2, Serotype-specific epitope 2a was inferred as being r elated to the backbone-located site D-Rha(alpha 1-3)D-Rha and epitope 2d to the immunodominant lateral (alpha 1-4)D-Fuc residue of OPS consi sting of tri-D-rhamnose repeats in the backbone, Epitope 2d alternated with 2a within the same LPS molecule and did not cross-react with epi tope Td, Serotypes O2a and O2d were observed in some strains correlati ng with the coexpression of the two chemotypes of OPS by the same stra in, The serogroup Ol-specific Mab Ps1a reacted weakly but definitely w ith all strains from serogroup O2, We propose serological formulas for serogroups O1 and O2 as well as for individual strains within these s erogroups.