Diagnosis of Brucella ovis infection of rams with an ELISA using protein G as conjugate.

The complement fixation and gel diffusion tests for Brucella ovis ram epididymitis were compared with an indirect ELISA using antigens from B ovis extracted in hot saline, rough B ovis lipopolysaccharide or a cytosolic fraction of rough B melitensis 115, and commercial anti-IgG (heavy and light chain specificity) or protein G conjugates. None of the antigens and conjugates used in the ELISA gave better results in terms of sensitivity and specificity than the complement fixation or the gel diffusion tests with the sera of 41 rams naturally infected with B ovis, 17 rams inoculated conjunctivally with B ovis and 53 Brucella-free rams. The protein G conjugate significantly reduced the background reactivity of the sera from the Brucella-free rams but did not improve the sensitivity of the ELISA with the anti-IgG conjugate.