ANTIGENICALLY STABLE 35 KDA OUTER-MEMBRANE PROTEIN OF SALMONELLA

Outer membrane protein (OMP) extracts from Salmonella species represen ting seven serogroups were examined by SDS-PAGE followed by immunoblot ting. Two major proteins with apparent molecular weight of 24 and 35 k Da were identified The latter protein was present only in Salmonella. Immunoblotting with a monoclonal antibody (MAb) IDS (IgA) demonstrated the 35 kDa OMP contains an antigen common for all tested Salmonella s pecies with the exception of atypical species such as S. arizona. The type of growth media had no effect on the antigenicity of 35 kDa prote in. However, the electrophoretic appearance of the 35 kDa protein was influenced by heat-treatment. Analysis of OMP extracts by SDS-PAGE and immunoblotting without heat-treatment revealed that MAb 1D6 bound sev eral isoforms of this protein, a major form at 28 kDa and about eight minor forms in the range between 34 and 40 kDa. None of these forms co ntained carbohydrate moieties that may be responsible for the polymorp hic appearance of the protein. These forms were converted to a single form by heat-treatment at 100 degrees C indicating that the 35 kDa OMP is most likely a heat-modifiable protein. Furthermore, extended heat- treatment (121 degrees C, 15 min) did not affect the antigenicity of t he 35 kDa OMP. Electron microscopy studies revealed that the 35 kDa OM P is exposed on a surface of the bacterial cells, although the frequen cy of epitopes recognized by the Mab 1D6 was low as can be inferred fr om the low number of gold particles attached to the cells.