Histological cross-sections of HAE cultures inoculated with wild type (wt), pilA, pilT and pscC strains. Representative images taken at 3, 6, and 12 hours post-infection are shown. Wild type P. aeruginosa rarely adhered to the ciliated mucosal surfaces but local infection foci could be detected after 3 hours. After breaching the mucosal barrier, the wild type strain interacted efficiently with the basolateral surfaces of ciliated cells and the underlying basal epithelial cells. Bacterial adherence was associated with host cell rounding and detachment. By 12 hours, the wild type infection appeared to spread between cells to encompass the entire HAE culture. In contrast, the non-piliated pilA mutant, the piliated non-retractile pilT mutant and the T3S mutant (pscC) did not interact with the epithelium or cause invasive infection. However, unlike the pilA mutant, the pilT and pscC mutants retained the ability to interact with shed or extruding epithelial cells (bottom right panels).