Virulence of B. abortus 2308 Δomp10 in the mouse model. Liver pathological section (A1-F1), the effect of 2308 on liver (A1, D1), the effect of Δomp10 on liver (B1, E1), the PBS control (C1, F1); Spleen pathological section (A2-F2), the effect of 2308 on spleen (A2,D2), the effect of Δomp10 on spleen (B2, E2), the PBS control (C2, F2).