Characterization of an outer membrane protein of Pasteurella multocida belonging to the OmpA family

The outer membrane vesicle and N-lauroylsarcosine-insoluble protein preparations of Pasteurella multocida 656 were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A major outer membrane protein (OMP) was found to be heat-modifiable, having a molecular mass of 28 kDa when the OMP preparation was solubilized at 60 degrees C and a molecular mass of 37 kDa when it was solubilized at 100 degrees C. A monoclonal antibody, designated mAb MT4.1, was generated against heat-modifiable OMP of P. multocida. This mAb reacted with the heat-modifiable OMP irrespective of the temperature at which it was solubilized, as demonstrated by immunoblot results. The heat-modifiable OMP of P. multocida showed a significant N-terminal amino acid sequence homology with OmpA family. Immunoelectron microscopic study revealed that the mAb Mt4.1 epitope was not surface exposed on the intact bacterium. The mAb MT4.1 reacted with all the reference strains of 5 capsular and 16 somatic serotypes, as well as with 75 field strains of P. multocida in immunoblot assay. This mAb MT4.1 also reacted with strains of various other Pasteurella species such as P. stomatis, P. aerogenes P. gallinarum, P. betti, P. sp, B, P. SP-g and P. canis, but not with strains of 12 other Gram-negative bacteria. These results indicated that this protein carried a genus-specific epitope and mAb MT4.1 may be useful for identification of Pasteurella species. This is the first report in which a major heat-modifiable OMP has been identified and characterized using a mAb, and has been shown belonging to the OmpA family.