Fusobacterium necrophorum, a Gram-negative, non-spore-forming anaerobe, is a normal inhabitant of the alimentary tract of animals and humans. Two types of F. necrophorum, subspecies necrophorum (biotype A) and funduliforme (biotype B), have been recognized, which differ morphologically, biochemically, and biologically. The organism is an opportunistic pathogen that causes numerous necrotic conditions (necrobacillosis) such as bovine hepatic abscesses, ruminant foot abscesses and human oral infections. The pathogenic mechanism of F. necrophorum is complex and not well defined. Several toxins, such as leukotoxin, endotoxin, haemolysin, haemagglutinin and adhesin, have been implicated as virulence factors. Among these, leukotoxin and endotoxin are believed to be more important than other toxins in overcoming the host's defence mechanisms to establish the infection. F. necrophorum is encountered frequently in mixed infections and, therefore, synergisms between F. necrophorum and other pathogens may play an important role in infection. Several investigators have attempted to induce protective immunity against F. necrophorum using bacterins, toxoids, and other cytoplasmic components. Generally, none of the immunogens has afforded satisfactory protection against Fusobacterium infections. Because of the unavailability of suitable immunoprophylaxis, the control of F. necrophorum infection has depended mainly on the use of antimicrobial compounds.

No abstract

A culture medium containing lactate as the sole energy source and antibiotics (bacitracin, gentamicin, and streptomycin) was used for selection and enumeration of Fusobacterium necrophorum from bovine ruminal contents. F. necrophorum growth was determined by indole production, and enumeration was performed by the most-probable-number technique. The number of F. necrophorum cells in cattle fed a 100% forage diet was 7 x 105/g of ruminal contents. The number increased (P < 0.05) 10-fold after the diet was changed to 85% corn grain. Fusobacterium necrophorlum, the primary etiologic agent of bovine hepatic abscesses, is a normal inhabitant of the bovine rumen (16). Hepatic abscesses in cattle are related to feeding of high-grain diets (9, 10). Rapid fermentation of grain in the rumen and the consequent accumulation of organic acids, particularly lactate, result in ruminal acidosis and rumenitis. F. necrophorum penetrates the damaged rumen epithelial wall, reaches the liver via the portal circulation, and causes abscesses (19). F. necrophorum has been detected in or isolated from bovine ruminal contents and ruminal lesions by an immunofluorescence technique (7), by culture methods (23, 26), and by injecting ruminal fluid intraperitoneally into rats (3). However, quantitation of F. necrophorum in ruminal contents is hampered by the lack of a selective medium. Therefore, we developed a method for selectively enumerating F. necrophorum in bovine ruminal contents. A modified lactate (ML) medium was used for selection and enumeration of F. necrophorum from bovine ruminal contents. The composition of ML broth (per liter) was as follows: 10 g of DL-lactate (United States Biochemical Co., Cleveland, Ohio), 10 g of tryptone (Difco Laboratories, Detroit, Mich.), 1 mg of hemin (Eastman Kodak Co., Rochester, N.Y.), 10 ml of vitamin B mixture (20), 38 ml each of mineral I (0.

The relationship between serum-neutralizing antibody against Fusobacterium necrophorum leukotoxin and hepatic abscesses was investigated in cattle fed diets supplemented with or without tylosin. Sixteen cattle (eight each in tylosin and in control groups) were inoculated intraportally with F. necrophorum. Ultrasonographic scanning showed that all control animals developed hepatic abscesses after inoculation. In the tylosin group, two animals were free of abscess by d 7 and one was free by d 14. Leukotoxin-neutralizing antibody titers were low on d 0, but increased (P < .05) markedly after intraportal inoculation in both groups. In a second study, blood was collected at the time of slaughter from 141 feedlot cattle (36 fed diets with tylosin and 105 fed diets without tylosin), and livers were examined for presence or severity of hepatic abscesses at slaughter. The incidences of hepatic abscesses were 32% in the control group and 6% in the tylosin group. Antibody was detected in all animals; however, antibody titers were greater (P < .05) in cattle with abscessed liver than those without, and greater (P < .01) in the nontylosin than in the tylosin group. Abscess score and antibody titer were correlated (r = .34; P < .0001). We conclude that F. necrophorum leukotoxin is highly antigenic and that anti-leukotoxin antibody titer is related to the severity of hepatic abscesses.

No abstract