Enhancement of the infectivity ofFusobacterium necrophorumby other bacteria

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Abstract
SUMMARY: Necrobacillosis is caused byFusobacterium necrophorum(FN), but other organisms are often present in the lesions. Their possible role was studied in experiments made with a virulent FN strain which, by itself, produced fatal necrobacillosis in mice provided that large doses ( > 106organisms, subcutaneously) were given. Mice were inoculated subcutaneously with FN suspended in sub-lethal doses (0·1 ml) of undiluted or diluted broth cultures of other bacteria. Undiluted culture of a strain ofEscherichia colireduced the infective dose of FX to < 10 organisms: in the necrobacillosis lesions that developed, fusobacteria greatly outnumberedE. coli. A heat-killed preparation or sterile filtrate ofE. coliculture had little if any effect on FN.Citrobacter freundiiand comparativelv small numbers ofCorynebacterium (Actinomyces) pyogenesproduced effects similar to that ofE. coli. An α-haemolvtic streptococcus.Pseudomonas aeruginosa.Bacteroides fragilisandFusobacterium nudeatumalso enhanced the infectivity of FN. though less strikingly thanE. coli. FN increased the persistence invivoof the α-haemolytic streptococcus andB. fragilis, and enabled the latter to multiply profusely.