Antigenically stable 35 kDa outer membrane protein ofSalmonella

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Abstract
Outer membrane protein (OMP) extracts from Salmonella species representing seven serogroups were examined by SDS‐PAGE followed by immunoblotting. Two major proteins with apparent molecular weight of 24 and 35 kDa were identified. The latter protein was present only in Salmonella. Immunoblotting with a monoclonal antibody (MAb) 1D6 (IgA) demonstrated the 35 kDa OMP contains an antigen common for all tested Salmonella species with the exception of atypical species such as S. arizona. The type of growth media had no effect on the antigenicity of 35 kDa protein. 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 several 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 contained carbohydrate moieties that may be responsible for the polymorphic appearance of the protein. These forms were converted to a single form by heat‐treatment at 100°C indicating that the 35 kDa OMP is most likely a heat‐modifiable protein. Furthermore, extended heat‐treatment (121°C, 15 min) did not affect the antigenicity of the 35 kDa OMP. Electron microscopy studies revealed that the 35 kDa OMP is exposed on a surface of the bacterial cells, although the frequency of epitopes recognized by the Mab 1D6 was low as can be inferred from the low number of gold particles attached to the cells.

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