Figure 5. Tir-mediated actin assembly by C. rodentium (Φstx_2dact) promotes colonization of the colonic mucosa.

(A) Fecal shedding by mice infected with the designated strain, represented as the mean CFU (± SEM) of groups of five mice. (*, p<0.05; **, p<0.01; and ***, p<0.001; by repeated measures 2-way ANOVA followed by Bonferroni post-tests). Data represent one of five experiments. (B) Fecal shedding by mice infected with C. rodentium (Φstx_2dact)Δtir/pTir_WT and C. rodentium (Φstx_2dact)Δtir/pTirY471F at six days post-infection (left panel). Luminal colonization was measured by determining CFU/ml of luminal washings (second panel). Intestinal colonization (cecum and colonic) was measured by determining CFU/mg of tissue homogenate at six days post-infection (right two panels). Data represent a compilation of eight experiments, with three-to-ten mice per group. Each data point represents one mouse. Horizontal line indicates the mean. Fold increase represents the fold change between colonization by C. rodentium (Φstx_2dact)Δtir/pTir_WT and C. rodentium (Φstx_2dact)Δtir/pTirY471F. Error bars indicate ± SEM. (**, p<0.01 and ***, p<0.001). (C) Cecal and colonic sections of mice infected with C. rodentium (Φstx_2dact)Δtir/pTir_WT or C. rodentium (Φstx_2dact)Δtir/pTirY471F were taken at ten days post-infection and stained with DAPI (blue) and anti-Citrobacter antibody (green). Fecal shedding by each strain was equivalent at both time points. Mice infected with C. rodentium (Φstx_2dact)Δtir/pTir_WT and C. rodentium (Φstx_2dact)Δtir/pTirY471F had fecal bacterial loads of 4.8×10⁷/g and 3.6×10⁷/g, respectively. Magnification of IF images is 600x. White arrows indicate bacteria.