ELECTROPHORETIC AND ANTIGENIC CHARACTERIZATION OF DERMATOPHILUS-CONGOLENSIS EXTRACELLULAR PRODUCTS

Dermatophilus congolensis is the causative agent of bovine dermatophil osis and lumpy wool in sheep. Two field isolates of D. congolensis, on e each from a cow in Ghana and a sheep in Scotland, were cultured for 24-72 h in a synthetic medium based on RPMI-1640, Culture filtrates we re examined by SDS-PAGE and considered to contain extracellular produc ts released by growing hyphae and filaments. Electrophoretic profiles of culture filtrates of the two isolates contained common bands and ba nds that were unique to each isolate, The composition of extracellular products altered with increasing culture periods indicating that spec ific products were released at different stages of growth. Culture fil trate prepared in the presence of serine protease and metalloprotease inhibitors contained more and better defined bands than that prepared without protease inhibitors indicating the presence of proteases in cu lture filtrates. Western blot analysis of extracellular products using a panel of sera showed that the two isolates from different host spec ies and distant geographical locations contained cross-reactive antige ns. Natural and experimental infections stimulated antibody responses to antigens in culture filtrates, sera from animals that were disease free but in-contact with dermatophilosis-infected animals also contain ed antibodies to extracellular antigens. The antigens recognised by mo st sera had molecular weights of 200 kDa in the bovine isolate, 170 kD a in the ovine isolate and 67, 27 and 52-55 kDa in both isolates, The number of antigenic bands of both isolates was positively correlated w ith the intensity of challenge and the severity of infection antibodie s in sera from disease-free cattle in Ghana recognised more antigens t han sera from disease-free sheep in Scotland and more antigens were re cognised by sera from chronically-infected Ghanaian cattle than by ser a from experimentally-infected calves and sheep. The latter developed antibodies to antigens of 27 and 24, kDa during the course of infectio n. The electrophoretic profiles of extracellular products of D. congol ensis are less complex than those of other structures of the bacterium yet they exhibit differences between the two isolates. Extracellular products contain antigens recognised by sera from naturally exposed an d experimentally-infected animals that may be involved in immunity to D. congolensis or immunopathogenesis of dermatophilosis. (C) 1997 Else vier Science B.V.