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Non-specific resistance of mice to Pasteurella haemolytica
Abstract:
A technique for challenge infection of mice with Pasteurella haemolytica is described. Mice were challenged intraperitoneally with P haemolytica in gastric mucin, and viable counts were performed 6 h later on liver suspensions. Viable counts of P haemolytica in the livers of unvaccinated control mice had increased 6 h after infection. Mice were injected subcutaneously with a commercial pasteurella vaccine at various time intervals before challenge. In those given vaccine two weeks, one week, 48 h and 1 h before challenge, viable counts of P haemolytica in the liver increased as for control mice. However, if the time interval between administration of vaccine and challenge was 12 or 24h, viable counts of P haemolytica in the liver decreased after challenge. Subcutaneous inoculation with the nonbacterial components of the vaccine 24 h before challenge did not cause such an effect. Inobulation with the vaccine 24h before challenge with Escherichia coli resulted in an increase in the LD50 for that organism, indicating that the effect is probably non-specific.
Insights
A novel mouse model for Pasteurella haemolytica infection shows that vaccination 12-24 hours before challenge enhances survival. This protective effect appears non-specific, suggesting broader immune modulation.
Area of Science:
- Veterinary Microbiology
- Immunology
Background:
- Pasteurella haemolytica is a significant pathogen in animal respiratory diseases.
- Developing effective challenge models is crucial for evaluating vaccines and understanding host-pathogen interactions.
Purpose of the Study:
- To establish a reliable challenge infection model for Pasteurella haemolytica in mice.
- To investigate the efficacy of a commercial Pasteurella vaccine at various pre-challenge intervals.
Main Methods:
- Mice were infected intraperitoneally with Pasteurella haemolytica suspended in gastric mucin.
- Bacterial viable counts in liver homogenates were assessed 6 hours post-infection.
- Mice received a commercial Pasteurella vaccine at different times before challenge.
Main Results:
- Unvaccinated mice showed increased bacterial counts, confirming successful infection.
- Vaccination 12 or 24 hours prior to challenge significantly reduced bacterial viable counts in the liver.
- Vaccination at other time points (1h, 48h, 1 week, 2 weeks) did not confer protection.
- The protective effect was not observed with non-bacterial vaccine components alone.
- Pre-challenge with the vaccine against Escherichia coli also showed increased LD50, suggesting a non-specific effect.
Conclusions:
- A 12-24 hour vaccination window confers transient protection against Pasteurella haemolytica challenge in mice.
- The observed protection may be mediated by a non-specific immune response rather than specific immunity.
- This model provides a valuable tool for studying bacterial infections and vaccine-induced immune responses.