FIG. 5.

Competition between the wild type and the sitA mutant in a plaque assay. Henle cells were infected with a mixture of equal numbers of wild-type (SM100) and sitA mutant (SM166) S. flexneri bacteria and incubated in the presence of gentamicin to kill extracellular bacteria. In each set of experiments, one of the two strains was marked with lacZ. Bacteria were harvested from the plaques after 72 h of incubation, and the competitive index (ratio of sitA mutant to wild-type bacteria recovered) was determined. Each symbol represents the competitive index in a single experiment. The average competitive index is shown by a horizontal line. The asterisks indicate that the P value (two-tailed t test) for the difference between the observed competitive index and an expected index of 1.0 is <0.02 for SM166 Lac/SM100 and <0.04 for SM166/SM100 Lac.