Fig 4.

Bacterial internalization is enhanced by the Ysa T3SS. Wild-type and mutant strains were assayed to measure the percentage of internalized bacteria as described in Materials and Methods. The percent intracellular bacteria was determined for each strain and normalized to the average for the wild-type (WT) strain in each assay (WT set to 100%); error bars represent the standard deviations. Strains tested are all pYV⁻ and carry in-frame deletions of a single ysp gene (ΔyspA-P) or all 9 ysp genes (Δysp9). The data are averages of at least 2 assays (n ≥ 8). Student's t test was performed to assess statistical significance. *, P = 0.001; **, P ≤ 0.0001.