A previously described mouse monoclonal antibody (WM25), directed against the caprine pathogenic mycoplasma strain F38 (Mycoplasma capricolum subspecies capripneumoniae), was further examined for its diagnostic efficacy in serological tests against various isolates of this group and of each of the five other 'M mycoides cluster' groups (M mycoides subspecies mycoides, small colony (SC) and large colony (LC) biotypes, M mycoides subspecies capri, M capricolum subspecies capricolum and bovine group 7) and M agalactiae. The methods used were the conventional disc-growth inhibition and colony-immunofluorescence techniques. The same strains were also tested against polyclonal rabbit antisera for each mycoplasmal group. With the polyclonal antisera, many cross reactions occurred between members of the different groups. The two F38-polyclonals gave cross reactions only against various M capricolum subspecies capricolum and bovine group 7 strains, apart from one of M mycoides SC in the immunofluorescence test only. The F38 monoclonal antibody gave more specific results, in that only the F38-type strains (M capricolum subspecies capripneumoniae) and three of the four bovine group 7 strains reacted positively in growth inhibition tests; the only heterologous reaction by colony immunofluorescence was with one M capricolum subspecies capricolum strain. The F38 monoclonal antibody, WM25, may therefore be useful for the specific serological identification of caprine F38-type isolates by the disc-growth inhibition method, which will exclude M agalactiae, M capricolum subspecies capricolum and the other members of the 'M mycoides cluster' associated with goats, but not bovine group 7 (which is not found in goats), which can be excluded by colony immunofluorescence tests.
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