Comparison of Dermatophilus Congolensis Precipitating Antigens Prepared by Three Methods

SUMMARY Dermatophilus congolensis antigens were prepared from nutrient broth and trypticase soy broth cultures by three methods: ammonium sulphate precipitation, trichloroacetic acid extraction of the bacterial cells and culture supernatant ultrafiltration. The ultrafiltration antigens were concentrated using either Amicon XM50 or YM10 membranes. The three antigen types were tested by the reverse single radial immunodiffusion (RSRID) and double immunodiffusion (DID) methods. Sharply defined multiple precipitation lines were demonstrated with serum from cattle with streptothricosis using the nutrient broth supernatant antigen concentrated on YM10 membranes. Only weak or diffuse lines were obtained with the XM50-concentrated and ammonium sulphate-precipitated antigens. No precipitins were demonstrated in sera from the vaccinated cattle. The RSRID method offered no advantage over the DID technique. Nutrient broth concentration was less complicated and more efficient than the other methods tested. However, ultrafiltration membranes with pore size of 50 000 daltons should be used to avoid antigen loss. Failure to demonstrate precipitins in serum from cattle vaccinated intradermally with D. congolensis may indicate that this route provides a different type of antigenic stimulus; other workers have elicited precipitin reactions using different vaccination procedures.