E. coli Facilitates Murine Campylobacter Infection Figure 3. Kinetic analyses of C. jejuni colonization in fecal samples of infant mice. Conventionally colonized 3-weeks-old infant (3W; open circles) and 3-months-old adult (3M; solid circles) mice were orally infected with C. jejuni strain ATCC 43431 (A) or B2 (B) as described in Methods. Kinetic analyses of pathogen densities were performed by quantification of live C. jejuni in fecal samples by cultural analysis (CFU, colony forming units) at day (d) 6 p.i. ** indicates significant differences (p,0.01) of C. jejuni 43431 loads in infected infant mice at d1 versus d3, d5, and d6 p.i. (C) E. coli loads in colonic samples taken from na¨ıve 3-weeks-old infant mice (3W, open diamonds) were compared to conventionally colonized 3-months- old adult mice (3M, open circles). (D) Kinetic analyses of disease activity of conventionally colonized 3-weeks-old infant mice following infection with C. jejuni strain ATCC 43431 (43431, open circles, n = 10) or B2 (solid circles, n = 12) were performed applying a standardized clinical score (see Methods). Numbers of animals harboring C. jejuni or E. coli out of the total number of analyzed animals are given in parentheses. Days past infection, medians (black bars) and significance levels (P-values) determined by Mann-Whitney-U test are indicated. Data shown were pooled from at least three independent experiments. doi:10.1371/journal.pone.0035988.g003 composition. In the present study we investigated the suscepti- bility of an initially resistant host to C. jejuni during acute and chronic intestinal inflammation. In our acute T. gondii-induced ileitis model colonization resistance against C. jejuni was completely abolished and the pathogen colonized the entire GI tract with high counts. Moreover, C. jejuni and commensal E. coli translocated into MLNs, spleen, and liver. Strikingly, C. jejuni could be cultured from cardiac blood samples in .90% of infected animals displaying severe ileitis indicating bacteremia and subsequent sepsis. The impact of intestinal inflammation in overcoming colonization resistance was further supported by the finding that IL-102/2 mice suffering from chronic colitis were susceptible to C. jejuni infection. This is well in line with previous findings of Mansfield et al. showing that C. jejuni induced significant clinical signs of enterocolitis following infection of IL- 102/2 mice [41]. However, in the IL-102/2 mice analyzed here PLoS ONE | www.plosone.org 6 May 2012 | Volume 7 | Issue 5 | e35988