Abstract
Experimental infection of Fusobacterium necrophorum biovar A in BALB/c mice was performed to approach the mechanism of liver abscess formation in cattle. Liver abscesses were formed in the mice inoculated intravenously or intraperitoneally with F. necrophorum, but not in those inotulated with Corynebacterium pyogennes or Bacteroides oralis. In such liver abscesses, a population of 3.6×109 viable cells of F. necrophorum was present. The bacterial counts in the lung, spleen, and kidney varied from 104 to 106 per gram. The liver abscess formation was enhanced when a mixture of F. necrophorum and C. pyogenes was inoculated into mice. When a mixture of F. necrophorum and B. oralis or Staphylococcus aureus was inoculated into mice, however, such pathogenic synergism was not recognized. In the mixed infections, a large number of C. pyogenes or B. oralis were recovered from the abscess portion where F. necrophorum had multiplied actively. From these results, it seems that C. pyogenes, often isolated from bovine liver abscess, may be a helper organism in development of liver abscess, and B. oralis and S. aureus are secondary invaders.
