Diagnosis of Corynebacterium pyogenes infection in pigs by immunodiffusion test with protease antigen

A protease antigen was prepared from the culture supernatant of Corynebacterium pyogenes by concentrating with a flash evaporator and ultrafiltration. It was adjusted to the concentration of 32 units by the single radial immunodiffusion with a tentative standard serum. In the immunodiffusion test, the antigen of 4 units reacted enough with sera having an antibody titer ranging from 1 to 128. As a result, it was decided that the antigen of 4 units should be used in the immunodiffusion test for the detection of protease antibody. By the immunodiffusion test, protease antibody was demonstrated in about 35% of 443 sera from pigs collected at random. The antibody titer showed the distribution of 2 peaks. The summits of the two peaks were seen at 4 and 32 of antibody titer, respectively. The valley between the two peaks was seen at 16 of titer. From the result, a diagnostic criterion of the immunodiffusion test was decided provisionally as follows: above 16 of antibody titer is positive, 1 to 8 suspect, and less than 1 negative. On the other hand, protease antibody was demonstrated in sera from 13 of 14 pigs carrying abscesses from which C. pyogenes had been isolated. Its titer was 8 (in 2 pigs), 16 (in 1), 32 (in 3), 64 (in 6), and 128 (in 1). From these results, it was proposed that the immunodiffusion test with protease antigen be used for the diagnosis of C. pyogenes infection in pigs.