Serological diagnostic potential of recombinant outer membrane protein (Omp31) from Brucella melitensis in goat and sheep brucellosis

Outer membrane proteins of Brucella have been classified as group 1 (94 or 88 kDa), group 2 (36–38 kDa), and group 3 (31–34 and 25–27 kDa). Two proteins of 25 and 31 kDa with only 34% of identity are included in group 3 and they are coded for by the omp25 and omp31 genes. Proposed study planned to detect antibodies to Brucella melitensis Omp31 in farm goats having history of B. melitensis induced abortions, in B. melitensis-infected goats and sheep. By enzyme-linked immunosorbent assay (ELISA), using recombinant Omp31 as antigen, of 872 farm goats antibodies to Omp31 were detected in 112 (12.8%) cases. Out of 14 naturally infected goats infected with B. melitensis 12 (85.7%) showed anti Omp31 antibodies. Out of 10 naturally infected sheep with Brucella ovis, antibodies to Omp31 were detected only in 6 (60%) cases and in 18 (81.8%) out of 22 cases infected with B. melitensis. Obtained results were also compared with the rose Bengal plate test (RBPT). In controlled experiments, sensitivity and specificity of recombinant Omp31 (rOmp31) ELISA and RBPT were also evaluated and it was found that former test is 100% specific though RBPT has slightly higher sensitivity. In this study, we found a significant difference between the two groups (B. melitensis and B. ovis infected) in terms of the percentage of positive reactions or signal level by an ELISA. The reactivity of the positive sera against the purified rOmp31 was also tested by Western blotting. Sera from B. melitensis-infected animals showed a strong reactivity in comparison to sera from B. ovis-infected animals. The potential diagnostic usefulness of this antigen in combination with other recombinant proteins from B. melitensis would be of great importance in future in eradication of brucellosis.