Fig. 4.

T6SS-1 is critical for efficient intercellular spread. (A) Invasion efficiencies by BtE264 or ΔclpV1 mutants 2 h postinfection in HEK293 cells. (B) HEK293 cells were infected and stained for bacteria (red) and actin (green) 8 h postinfection. (Scale bar, 20 μm.) (C) Time course of intracellular replication in HEK293 cells. (D) Plaque-forming efficiency on HEK293 cell monolayers 18 h after infection. (E) Cytotoxicity assays in HEK293 cells. All assays in A and C–E were performed in triplicate and error bars represent ±SEM. **P < 0.05; *P < 0.005.