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The pathogenic properties of Fusobacterium and Bacteroides species from wallabies and other sources
Abstract:
Intracerebral inoculation was more effective than intraperitoneal, intravenous or subcutaneous inoculation as a means of producing lethal infections with Fusobacterium necrophorum in mice. Strains varied in virulence but, of five examined, two had LD50 values as low as ca. 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. varium and F. necrogenes) and of 22 strains belonging to 10 Bacteroides spp. was without apparent effect on mice, except for a slight transient illness in some animals given B. fragilis. This organism (five strains) differed from the other Bacteroides spp. 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 of B. fragilis in endogenous infections in man. There was no evidence that B. fragilis multiplied in the brain or that intravenous vaccination with a large dose of heat-killed homologous culture affected the rate at which it was eliminated.
Insights
Intracerebral inoculation effectively caused lethal Fusobacterium necrophorum infections in mice. Vaccination failed to protect against this lethal challenge, highlighting the bacteria
Area of Science:
- Microbiology
- Bacteriology
- Infectious Disease
Background:
- Fusobacterium necrophorum is a bacterium known to cause infections.
- The pathogenicity of Fusobacterium species in animal models requires further investigation.
- Understanding routes of infection and virulence factors is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the pathogenicity of Fusobacterium necrophorum in mice.
- To compare the efficacy of different inoculation routes for inducing lethal infections.
- To assess the potential of vaccination in preventing F. necrophorum infections.
Main Methods:
- Intracerebral, intraperitoneal, intravenous, and subcutaneous inoculation of mice with Fusobacterium necrophorum.
- Determination of lethal dose 50 (LD50) values for different strains.
- Intravenous vaccination with heat-killed bacteria followed by intracerebral challenge.
- Inoculation of mice with other Fusobacterium and Bacteroides species.
Main Results:
- Intracerebral inoculation was the most effective route for inducing lethal F. necrophorum infections.
- Virulence varied among strains, with LD50 values as low as 8,000 organisms.
- Profuse bacterial multiplication occurred in the brain.
- Intravenous vaccination did not protect against intracerebral challenge.
- Other Fusobacterium species and most Bacteroides species showed limited pathogenicity.
- Bacteroides fragilis was eliminated more slowly from the mouse brain compared to other Bacteroides species.
Conclusions:
- Intracerebral inoculation is a highly effective method for establishing lethal Fusobacterium necrophorum infections in mice.
- Current vaccination strategies using heat-killed bacteria are ineffective against intracerebral F. necrophorum challenge.
- Bacteroides fragilis exhibits unique clearance kinetics in the mouse brain, potentially relevant to its role in human infections.