Abstract
A total of 18 strains of Fusobacterium necrophorum, of which 15 were freshly isolated from bovine liver abscesses, apparently normal bovine liver tissues, bovine rumen fluids and heifer mastitis secretions, were submitted to detailed characterization of overall cultural and biochemical properties, guanine-plus-cytosine (G+C) contents of deoxyribo-nucleic acids and pathogenicity for mice. The strains were divided into two groups on the basis of colonial and cellular morphologies, growth mode in liquid medium, hemagglutination titer and pathogenicity for mice. The two groups of organisms were considered to correspond to bivars A and B of Fievez in F. necrophorum. This differentiation of groups was substantiated by the results of deoxyribonucleic acid homology tests; the homology indices among the strains of the two groups were 53 to 76%. This level of deoxyribonucleic acid homology was in accordance with that of subspecies proposed by Johnson for the genetic definition of taxonomic groupings.
