FIG. 4.

Comparison of isogenic pairs of plasmid-carrying and plasmid-cured strains of S. flexneri. The negative control (−) (gray bar) represents PMN transmigration to HBSS(+) buffer in the absence of bacteria or a chemotactic stimulus. A positive control was established as described in the legend to Fig. 2 ([30.72 ± 5.32] × 10⁴ CE). Data are means and SD for four monolayers in a single experiment and are representative of four separate experiments, all showing the same result.