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 103, 104, and 105 CFU. Recovery of brucellae from the lungs was possible early in infection with 101, 103, and 105 CFU, but only the group inoculated with 105 CFU consistently yielded quantifiable bacteria. At a dose of 101 CFU, few organisms were located in the spleen. Bacteria were recovered up to 140 days after inoculation in mice given 103 CFU. At an inoculum of 105 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. (Am J Vet Res 2001;62:398–405)