A semiquantitative enzyme method for identifying Fusobacterium necrophorum biovars A and B.

Abstract

The present study describes a semiquantitative enzyme method for distinguishing among the pathogenic biovars of Fusobacterium necrophorum. Since 1891 when McFaydean first described the organism as the etiologic agent of a bovine and ovine hepatic necrosis, numerous investigators have made significant contributions to the characterization and nomenclature of the bacterium. In 1963, Fievez classified the 3 Sphaerophorus species as one species, S. necrophorus, with biovars A, AB, B, and C. Beerens et a1. in 1971 similarly characterized the 3 Sphaerophorus species as follows: S. necrophorus was hemolytic, had a hemagglutinin, and was pathogenic for mice; S. funduliformis was hemolytic, had no hemagglutmm, and demonstrated only slight pathogenicity for mice; and S. pseudonecrophorus was not hemolytic, had no hemagglutinin, and was not pathogenic for mice. Biovars A and AB as described by Fievez corresponded to S. necrophorus, biovar B corresponded to S. funduliformis, and biovar C corresponded to S. pseudonecrophorus. In 1970, the International Committee on Nomenclature of Bacteria Taxonomic Subcommittee for Gram-Negative Anaerobic Rods recommended that the genus Sphaerophorus be included in the genus Fusobacterium. 3 The present classification of F. necrophorum, as described in 1984 in the first edition of Bergey’s Manual of Systematic Bacteriology 9 is based on biochemical characteristics, whereas the biovars of F. necrophorum, which have differences in cellular and colony morphology, are identified by their biological characteristics. Forty-two strains of F. necrophorum that had been previously isolated from bovine foot rot, bovine hepatic abscesses, 5 bovine ruminal contents and ovine hepatic abscesses were biotyped (Table 1) on the basis of direct hemagglutination (DHA) of chicken erythrocytes, sedimentation in broth culture, colony characteristics on enriched brain-heart infusion blood agar (BHIBA), and cellular morphology observed on gram-stained slides. The DHA tests were conducted as previously described. Twenty strains were identified as biovar A; 21 as biovar B; and 1 as biovar AB, which has morphologic characteristics of both biovars A and B and falls between these biovars on the basis of DHA and sedimentation pattern. The 42 strains were evaluated for their enzyme activities on 19 substrates using a commercial semiquantitative enzyme system as described by the manufacturer. Briefly, colonies from a BHIBA plate that had been incubated anaerobically in an atmosphere of 10% carbon dioxide, 10% hydrogen, and 80% nitrogen for 48 hours were suspended in