Culture filtrate proteins of Dermatophilus congolensis

In previous studies on the antigens of Dermatophilus congolensis very little attention has been given to the hyphae and to excreted-secreted products (ESP) of actively growing bacteria. In this study we have grown four isolates of D. congolensis in a serum free synthetic liquid culture medium based on RPMI 1640. Diafiltration and ultrafiltration were used to prepare ESP from infected culture fluid. These methods produced sufficient quantities of ESP that the polypeptide profiles of the four isolates could be examined by SDS-PAGE and Western immunoblotting. The four isolates produced a large number of polypeptides in culture, most of which were produced by all four isolates. However each isolate produced polypeptides that were unique to it. Western immunoblotting studies using pooled sera from chronically affected animals from Ghana showed that a number of polypeptides in ESP of a Ghanaian isolate were antigenic. When the same sera was tested against ESP from a Scottish isolate a number of polypeptides of the same molecular weight as those in the Ghanaian isolate and some at different molecular weights were recognized. This indicates that isolates of D. congolensis from different geographical areas produce ESP with shared antigenic determinants.