The <i>aer</i> and <i>tsr</i> genes confer a competitive growth advantage during colitis.

<p>Groups of streptomycin pre-treated mice (<i>N</i> is indicated below the graph in panel A) were inoculated with equal mixtures of the indicated <i>S</i>. Typhimurium strains and organs were collected for analysis four days after infection. Mice were infected either with an equal mixture of two strains (black bars in panel B) or with an equal mixture of the <i>S</i>. Typhimurium wild type (+ wt) and two mutant strains (white bars in panel B). (A) Induction of transcripts encoding the inflammatory markers Kc (encoded by the <i>Kc</i> gene, black bars) and iNOS (encoded by the <i>Nos2</i> gene, white bars) in the murine cecum after infection with the indicated mixtures of <i>S.</i> Typhimurium strains. Expression of <i>Kc</i> and <i>Nos2</i> in the cecal mucosa was determined by quantitative real-time PCR analysis. Bars represent geometric means of <i>Kc</i> and <i>Nos2</i> mRNA copy numbers as fold-change over mRNA levels in mock-infected mice ± standard error. (B) Competitive indices (CI) of <i>S</i>. Typhimurium strains recovered from the colon contents of infected mice. Bars represent geometric means ± standard error. *, <i>P</i><0.05; ns, not significant.