FIG. 3.

Cytotoxicity time course for HEp-2 cells. Y. pestis KIM5 and mutant derivatives were added to HEp-2 cells, and cell rounding was observed at hours 2 (A, D, and G), 4 (B, E, and H), and 8 (C, F, and I). Strains were grown at 28°C and pH 7 (A to C), 37°C and pH 7 (D to F), or 37°C and pH 6 (G to I) prior to infection of cells. Cytotoxicity was quantified by counting rounded cells in 5 fields/strain (n, ∼500 cells). Δ3 denotes KIM5 Δail Δpla ΔpsaA. *, P < 0.05; **, P < 0.00005; ***, P < 0.000005. Error bars represent standard deviations.