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Published on: January 17, 2014
Bacteriologic and histologic features in mice after intranasal inoculation of Brucella melitensis
M G Mense1, L L Van De Verg, A K Bhattacharjee
1Department of Diagnostic Pathology, Walter Reed Army Institute of Research, Silver Spring, MD 20910-7500, USA.
Objective:
To characterize effects of intranasal inoculation of virulent Brucella melitensis strain 16M in mice.
Animals:
Female Balb/c mice, 6 to 8 weeks old.
Procedure:
Studies were designed to elucidate gross morphologic lesions, bacterial burden in target organs, and histologic changes in tissues following experimental intranasal inoculation of mice with B melitensis 16M, which could be used to characterize a model for testing vaccine efficacy.
Results:
Measurable splenomegaly was evident at 3 and 7 weeks after inoculation. A demonstrable increase in splenic colony-forming units (CFU) from infected mice increased over time with increasing dose when comparing inocula of 10(3), 10(4), and 10(5) CFU. Recovery of brucellae from the lungs was possible early in infection with 10(1), 10(3), and 10(5) CFU, but only the group inoculated with 10(5) CFU consistently yielded quantifiable bacteria. At a dose of 10 CFU, few organisms were located in the spleen. Bacteria were recovered up to 140 days after inoculation in mice given 10(3) CFU. At an inoculum of 10(5) CFU, bacterial counts were highest early in infection. Histologic examination of tissues revealed an increase in white pulp and marginal zone in the spleen and lymphohistiocytic hepatitis.
Conclusion And Clinical Relevance:
Changes in the spleen and liver increased with increases in dose and with increased time following intranasal inoculation with B melitensis 16M. Surprisingly, histologic changes were not observed in the lungs of inoculated mice.
Insights
Intranasal inoculation of virulent Brucella melitensis strain 16M in mice caused dose-dependent spleen and liver changes. This study establishes a mouse model for Brucella vaccine efficacy testing.
Area of Science:
- Microbiology
- Immunology
- Pathology
Background:
- Brucella melitensis is a significant zoonotic pathogen.
- Intranasal inoculation is a potential route for vaccine delivery.
- A robust animal model is needed for evaluating Brucella vaccines.
Purpose of the Study:
- To characterize the effects of intranasal inoculation with virulent Brucella melitensis strain 16M in mice.
- To establish a model for testing vaccine efficacy against Brucella infection.
Main Methods:
- Female Balb/c mice were intranasally inoculated with varying doses of Brucella melitensis 16M (10^1 to 10^5 CFU).
- Gross morphologic lesions, bacterial burden in target organs (spleen, lungs), and histologic changes were assessed.
- Splenomegaly, splenic colony-forming units (CFU), and tissue histology were evaluated at different time points.
Main Results:
- Splenomegaly and increased splenic CFU were observed, correlating with dose and time post-inoculation.
- Brucella were recoverable from lungs early in infection, with higher doses yielding quantifiable bacteria.
- Histologic examination revealed splenic white pulp and marginal zone expansion, and lymphohistiocytic hepatitis.
Conclusions:
- Intranasal inoculation with Brucella melitensis 16M induces dose- and time-dependent changes in the spleen and liver.
- The observed pathology supports the use of this model for evaluating vaccine efficacy.
- Unexpectedly, no significant histologic changes were noted in the lungs.
