trans complementation of ΔyopM Y. pestis KIM5 in spleen but not in liver. C57BL/6 mice were infected i.v. with 5 × 103 CFU ΔlacZ Y. pestis KIM5-3003 (parent strain in terms of the yopM gene) or ΔyopM strain separately or as a 1:1 mixture and analyzed for CFU in spleen and liver on days 2, 3, and 4 p.i. Mix-P, ΔlacZ parent strain CFU from mice infected with the mixture; Mix-M, ΔyopM mutant CFU from mice infected with the mixture. The points at time zero represent the doses given to the mice. Each datum point represents the average of values from 8 mice. δ, P < 0.05, and δδ, P < 0.01, for mice infected with Mix-P and P; ψ, P < 0.05, and ψψ, P < 0.01, for mice infected with Mix-M and M; *, P < 0.05, and **, P < 0.01, for mice infected with M and P; #, P < 0.05, and # #, P < 0.01, for mice infected with Mix-M and Mix-P.