Fig 2.

A Brucella abortus mucR mutant is significantly attenuated in the mouse model. (A) Brucella abortus 2308, the mucR isogenic mutant strain (ΔmucR), and the complemented mucR mutant strain (ΔmucR::pC³030) were tested for survival and replication in primary murine macrophages. Macrophages were isolated from the peritoneal cavities of C57BL/6 mice, and the cells were infected with opsonized Brucella strains. Extracellular bacteria were killed by gentamicin treatment. At the indicated times, the macrophages were lysed, and serial dilutions were plated on blood agar to determine the number of viable intracellular brucellae. The asterisks indicate significant differences in survival and replication between parental strain 2308 and the mucR mutant strain (t test; P < 0.05). (B) Spleen colonization of mice experimentally infected with Brucella strains. C57BL/6 mice were infected intraperitoneally with approximately 5 × 10⁴ CFU of B. abortus 2308 or the mucR mutant. At 1 and 4 weeks postinfection, the mice were sacrificed, and the serial dilutions of spleen homogenates were plated on blood agar to determine the number of brucellae colonizing the spleen. The asterisks indicate significant differences in spleen colonization between parental strain 2308 and the mucR mutant strain (t test; P < 0.05).