ANTIGENS FOR SEROLOGICAL DIAGNOSIS OF OVINE FOOTROT

An antigen extracted from Dichelobacter nodosus with potassium thiocya nate (KSCN) is currently used in enzyme-linked immunosorbent assay (EL ISA) for serological diagnosis of ovine footrot, but the test lacks sp ecificity in mature sheep. Other antigens were therefore evaluated for use in this test. Structural components of the cell envelope of D. no dosus including outer membrane, cytoplasmic membrane, lipopolysacchari de and pilus and extracellular proteases were purified from cultured D . nodosus while recombinant membrane proteins, protease and pilus anti gens were also evaluated. Many antigenic components of D. nodosus part icipated in reactions in ELISA that were not specific for infection wi th D. nodosus and apart from pilus, none of the antigens resulted in i mproved specificity of the ELISA, Using a positive-negative cut-off to yield sensitivity of 70%, ELISA using pill from cultured D. nodosus s erogroup A had a specificity of 98.3% compared with 89.7% for the ELIS A with KSCN-extract as antigen (P < 0.001), Recombinant pill morphogen etically expressed in Pseudomonas aeruginosa were unsuitable for use i n ELISA due to copurification of Pseudomonas antigens to which apparen tly healthy sheep directed antibodies. The application of ELISA with D . nodosus pilus as antigen in footrot control programs is discussed.