FIG. 2.

Rat but not mouse serum is bactericidal to the ΔompX strain. Y. pestis KIM6⁺ and its isogenic ΔompX derivative were grown to mid-exponential phase at 28°C; incubated in 50% normal mice serum (NMS), normal rat serum (NRS), or the respective heat-inactivated sera (HIS) for 0, 1, and 2.5 h at 37°C; and plated on LB agar. Graphs represent surviving bacteria after incubation with NMS and NRS as a percentage of the number of bacteria that survived treatment with HIS (100%). A significant effect of the type of serum for the ΔompX strain was observed (repeated-measures ANOVA, P < 0.001). Results are the mean ± standard errors of the means (SEM) from data derived from two assays performed on separate days (n = 4).