FIG 3.

T3SS-1 is not functional in S. Paratyphi A grown to the late logarithmic phase aerobically. S. Typhimurium SL1344 (STM) and S. Paratyphi A 45157 (SPA) and their isogenic invA and invG null mutant strains were grown to the late logarithmic phase aerobically (A and B) or in LB supplemented with 0.17 M NaCl under microaerobic conditions (C and D), as described for Fig. 1, and used to infect Caco-2 cells. Under these conditions, the invasion rates of S. Paratyphi A were 0.06% ± 0.02% and 5.1% ± 1.7% (from the infection inoculum), respectively. Salmonella invasion was determined at 2 h p.i. using the gentamicin protection assay and is shown relative to the invasion of the wild-type background. One-way analysis of variance (ANOVA) with Dunnett's multiple-comparison test was implemented to compare the invasion of the different strains to that of the wild type. ***, P < 0.0001; ns, not significant.