The pathogenic properties ofFusobacteriumandBacteroidesspecies from wallabies and other sources

Abstract

SUMMARYIntracerebral inoculation was more effective than intraperitoneal, intravenous or subcutaneous inoculation as a means of producing lethal infections withFusobacterium necrophorumin mice. Strains varied in virulence but, of five examined, two had LD50 values as low asca. 8000 and 14000 viable organisms. Profuse bacterial multiplication in the brain was demonstrated. Intravenous vaccination with a single large dose of heat-killed whole culture or washed bacterial cells failed to protect against intracerebral challenge.Intracerebral injection of other fusobacteria (F. nucleatum, F. variumandF. necrogenes) and of 22 strains belonging to 10Bacteroidesspp. was without apparent effect on mice, except for a slight transient illness in some animals givenB. fragilis. This organism (five strains) differed from the otherBacteroidesspp. tested, which included eight strains belonging to the fragilis group, in being eliminated more slowly from the mouse brain – a point that may be relevant to the special pathogenicity ofB. fragilisin endogenous infections in man. There was no evidence thatB. fragilismultiplied in the brain or that intravenous vaccination with a large dose of heat-killed homologous culture affected the rate at which it was eliminated.