Probiotic <i>E. coli</i> Nissle (EcN) initially induces intestinal inflammation that is qualitatively and quantitatively similar to early responses to <i>Salmonella</i>.

<p><b>A</b>) Polymorphonuclear neutrophils (PMN, magenta) accumulate close to EcN (yellow) in the dome area of murine Peyer’s patches 3 h after intragastric EcN administration. Bacteria are cleared and inflammation resolves within 48 h after administration. The scale bar represents 100 µm. Similar results were obtained for 12 mice in three independent experiments. <b>B</b>) Phenotype of infiltrating CD11b⁺ host cells 3 h post infection. The majority of cells represent PMN’s (Ly-6G^hi Ly-6C^mo), some other cells represent mobile monocytes (Ly-6G^lo Ly-6C^hi). <b>C</b>) Colonization levels of EcN (open triangles) and PMN infiltration (filled circles) in Peyer’s patches at various time intervals post infection (d.t., detection threshold for plating). The data might overestimate actual bacterial tissue loads due to potential contamination with residual luminal EcN especially at early time points after oral administration. Means and standard deviations are shown for groups of three to four mice. Similar data were obtained in four independent experiments. <b>D</b>) PMN infiltration 3 h post EcN administration in wildtype C57BL/6 mice (B6) and mutant mice with various defects in innate immunity. Data for sham-infected B6 are also shown (open circles). Significance of differences to infected B6 was determined using t-test on log-transformed data (**, <i>P</i><0.01; *, <i>P</i><0.05; n.s., <i>P</i>>0.05). Similar data were obtained in two independent experiments.