Outer membrane proteins (OMPs) of three strains of B. abortus i.e. S19, RB51 and a local field isolate of biotype 1 were isolated through disrupting cells to generate membranes by centrifugation and sodium lauryl sarcosinate solubilisation of inner membrane proteins. Distinct OMP profiles of each strain were seen on SDS-PAGE. SDS-PAGE analysis of S19 and field isolate revealed eight protein bands in each strain.  The OMPs of S19 had molecular masses 89.0, 73.0, 53.7, 49.0, 38.0, 27.0, 22.3, and 17.7 kDa, while field isolate had OMPs of 151.3, 89.0, 75.8, 67.6, 37.0, 27.0, 24.0 and 19.0 kDa. B. abortus RB51 yielded 11 OMP bands ranging from 12.5 to 107.1 kDa, with 34.2, 15.8 and 12.5 kDa as additional OMPs.  Western immunoblot analysis using antisera raised against all three strains in buffaloes indicated an almost similar pattern of immuno-reactive OMPs in S19 and field strain. Two OMPs of molecular weight 37-38 and 19 kDa were immuno-reactive in all strains in buffaloes. There is possibility of use of these OMPs in a recombinant vaccine for B. abortus. A distinct protein of molecular weight of 151.3 kDa was identified in field strain but not in both vaccine strains of B. abortus. Use of this OMP in a diagnostic assay may differentiate between vaccinated and infected animals.

Key words: Protein profiling, Western blot analysis, Outer membrane proteins, Brucella abortus, RB51, S19, Buffaloes