Serological characterization of fluorescent Pseudomonas strains cross-reacting with antibodies against Erwinia chrysanthemi

Sixteen bacterial strains, cross-reacting with antibodies againstErwinia chrysanthemi (Ech), were isolated from potato peel extracts, ditch water, and the rhizosphere of wheat, onion, sugar beet and chicory using the immunofluorescence colony-staining procedure. Based on fatty acid profiles, isolates were classified as belonging to thePseudomonas fluorescens group.These strains, together with two previously isolated cross-reactingP. fluorescens strains, crossreacted with polyclonal antibodies against Ech in immunofluorescence cell-staining, Ouchterlony double diffusion, and ELISA. Seventeen strains also reacted strongly with monoclonal antibodies against the lipopolysaccharides (LPS) of Ech in ELISA.Cell envelopes (CE) and proteinase-K-treated CE (mainly LPS) of cross-reacting bacteria were further characterized with SDS-PAGE and Western blotting. Based on CE protein and LPS patterns, the cross-reacting bacteria were classified into two groups, each existing of two subgroups. Both CE and proteinase-K-resistant antigens strongly cross-reacted on immunoblots with antisera against a wild type strain of Ech. With an antiserum against a LPS O-chain lacking mutant of Ech only protein bands but no proteinase-K-resistant antigens were detected on immunoblots. These data suggest that in all cases the highly antigenic LPS O-chain is responsible for the cross-reactions.