SUMMARY: The K99 antigen common to some bovine strains of caused mannose-resistant haemagglutination of sheep erythrocytes and was shown to be responsible for the attachment of K99-positive bacteria to calf brush-border preparations because (i) strains grown at 18° did not produce K99 antigen, cause haemagglutination, or attach to brush borders; (ii) a 12 (K99) recombinant strain showed both haemagglutinating activity and attachment to brush borders whereas, before it received the K99 plasmid, the recipient strain was negative in both respects; and (iii) cell-free extracts of K99 antigen showed haemagglutinating activity and inhibited the attachment of K99-positive organisms to brush borders.

K99 antigen appears to be a virulence determinant in the pathogenesis of neonatal calf diarrhoea. It is readily demonstrated by haemagglutination and brush-border attachment tests.


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