It had already been shown with a single virulent strain (A42) of Fusobacterium necrophorum that suspension of the fusobacteria in sub-lethal doses of broth cultures of other bacteria reduced the minimum infective dose (> 106 organisms) for mice by subcutaneous inoculation, sometimes to < 10 organisms. The present study extended the known range of bacteria with strong infectivity-enhancing properties to include Bacillus cereus, Klebsiella oxytoca and Staphylococcus aureus; and of those with weaker effect to include Bacillus subtilis, ‘Bacteroides melaninogenicus’, Clostridium sporogenes, Pasteurella haemolytica, and Proteus mirabilis.
The study also showed that five further virulent strains of F. necrophorum closely resembled A42 in respect of striking susceptibility to infectivity enhancement by Escherichia coli, Actinomyces (Corynebacterium) pyogenes and S. aureus. One further strain (A6) of F. necrophorum resembled A42 in respect of strong infectivity enhancement by A. pyogenes, S. aureus, B. cereus and K. oxytoca but differed from it and the other five strains in being only slightly affected by E. coli.
This work was a necessary prelude to the development of a method, based on infectivity enhancement, for the detection and isolation of F. necrophorum present in small numbers in heavily contaminated material such as faeces.