Bacterial propagation below an epithelial monolayer.

<p>(<b>A</b>) A wound was made in MDCK monolayers and bacteria were subsequently introduced in the medium. Invasion from the wound was recorded in the basal compartment by confocal microscopy at different time points, as illustrated in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005377#ppat.1005377.s005" target="_blank">S4 Fig</a> The wounded monolayers were infected with the wild type or with mutants lacking T3SS (Δ<i>pscF</i>), flagellum (Δ<i>fliC</i>) or pili (Δ<i>pilY1</i>). The invasion surfaces were measured in 8 fields. The data represent the averaged percentages of invaded surfaces (+ SEM) of total field surface minus the wounded area. (<b>B</b>) MDCK-EGFP monolayers were infected with CHA and bacteria progression was recorded by confocal microscopy in the basal compartment (<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005377#ppat.1005377.s014" target="_blank">S8 Movie</a>). Bacteria were tracked using ImageJ software MTrackJ. Once bacteria assembled in rafts, the leading bacterium was recorded. The box-plots represent the instantaneous velocities recorded in 4 movies for each condition. N = 640 velocities from 40 trajectories at 4–5.5 hpi, and n = 455 velocities from 20 trajectories beyond 7 hpi. Data were significantly different at 4–5.5 and beyond 7 hpi, using Mann-Whitney's test (p < 0.001). (<b>C</b>) Similar experiment with Δ<i>fliC</i> (see <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005377#ppat.1005377.s015" target="_blank">S9 Movie</a>). Box-plot showing the instantaneous velocities (n = 1360) of Δ<i>fliC</i> from 35 trajectories in 4 different movies.