Antigenic cross-reactions between the causative agent of ovine footrot, Dichelobacter nodosus, and other bacteria

Abstract

Lack of test specificity for the causative agent of ovine footrot, Dichelobacter nodosus, currently precludes routine application of serological tests. To investigate this problem antigenic cross-reactivity between D. nodosus and other bacteria was studied using double immunodiffusion and enzyme-linked immunosorbent assay (ELISA). Sera from sheep and rabbits immunised with D. nodosus reacted with other taxa but particularly Yersinia pseudotuberculosis, Y. enterocolitica, Cardiobacterium hominis, Suttonella indologenes, Corynebacterium pseudotuberculosis, Brucella ovis, Proteus vulgaris and Histophilus ovis. Sheep sera were then adsorbed with bacterial antigens and reacted in ELISA with cell envelope antigens of D. nodosus to determine whether non-specific reactivity could be reduced. C. pseudotuberculosis and the antigenically related organisms Nocardia asteroides and Mycobacterium phlei, as well as Bacteroides ruminicola and several other taxa reduced the signal in the ELISA. Antibodies reactive with many taxa increased with age of sheep. Sheep sera were more cross reactive than rabbit sera and distinguished relatively poorly between the antigens of different bacteria. Unfortunately the simple expedient of immunoadsorption was not effective in reducing non-specific reactions to the extent required for practical application of a serological test for ovine footrot.