Fig 5.

Ifp complements cell adhesion function of InvA. (A) Cell adhesion and invasion efficiencies of Y. pseudotuberculosis YP9 (ΔinvA) expressing Ifp (pFU08), Ifp_His6 (pFU140), InvC (pFU209), or InvC_His6 (pFU210) were determined with human epithelial cells. Strains harboring the empty vector plasmid pBADmycA were used as a negative control. About 5 × 10⁶ bacteria were used to challenge 5 × 10⁴ cells, and the samples were incubated for 30 min at 20°C to determine cell attachment or at 37°C to monitor invasion efficiency. The data are presented as means ± standard deviations from three independent experiments performed in triplicate. Data were analyzed by the Student's t test. Asterisks indicate results that differed significantly from those for YPIII pBADmycA (P < 0.05). (B) E. coli K-12 cells harboring the empty vector pBAD-Myc, pFU140 (Ifp⁺), or pFU210 (InvC⁺) were used to infect polarized Caco-2 cells. Adherent bacteria were visualized by scanning electron microscopy and are indicated by white arrows. The black bars indicate 5 μm. (C and D) Monolayers of differentiated Caco-2 cells were challenged with YPIII, YP97 (Δifp), and YP98 (ΔinvC) and incubated for 3 h at 25 and 37°C to monitor cell attachment (C) and invasion (D). The total numbers of adherent and internalized bacteria were determined as described in Materials and Methods. The data represent the means ± standard deviations from three independent assays done in triplicate. Data were analyzed by the Student's t test. The asterisks indicate results that differed significantly from those for YPIII: *, P < 0.05; **, P < 0.01.