Animals were euthanized at 24, 48, 72, 96 and 168 h, and the number of colonies recovered from the cecum and counted on antibiotic-containing media

was used to calculate the competition index (CI). The CI is the ratio of mutant to wild-type CFU in output samples/mutant to wild type CFU in the inoculum. A CI value of 1 (shown by the black line) indicates that the mutant competes equally with the wild-type strain. Bars represent the geometric mean with the 95% confidence interval. The CIs of samples from the same intestinal site were compared by the Mann Whitney non-parametric test. Discussion Shiga toxin-producing E. MK-2206 concentration coli O104:H4 is a recently identified emerging pathogen that caused an outbreak resulting in a large number of HUS cases and fatalities in adults. Although the serotype O104:H4 was previously isolated in 2001 from a child presenting HUS [9] and in 2006 from a woman who contracted HUS in Korea [26], the unprecedented number of cases, lethality, and complications resulting from the infection identifies this strain as a public threat to human health. The intestinal disease that arises from the E. coli O104:H4 causing the outbreak seems to be the result of a hybrid infection that developed from recombination of the Shiga toxin genes from STEC O157:H7 into an EAEC strain, which became evident after sequencing the genome of this isolate [3–5]. Despite the extensive body of literature available regarding

STEC and EAEC infections and the study of the pathogenic mechanisms, no data are available on the virulence mechanisms of hybrid strains, as in the case of E. coli O104:H4. Data collected by our group and others demonstrated that Small molecule library in vivo bioluminescence imaging is a valuable tool for providing insights into mechanisms of pathogenesis, with the goal of identifying new virulence or colonization properties [18, 19]. In the current study, it was demonstrated that E. coli O104:H4 infection

in the streptomycin-treated mouse colonization model can be Isotretinoin monitored by using RJC001, a bioluminescent strain of E. coli O104:H4. BLI has been used to study the mechanisms of pathogenesis and treatment efficacies for a number of infectious enteric bacteria. One of the first investigations using BLI was conducted to monitor the virulence differences among strains of Salmonella enterica serovar Typhimurium [27]. In that study, the authors showed the utility of the bioluminescence system by visualizing the efficacy of antibiotic treatment in infected animals. BLI in E. coli has also been used to track EAEC colonization in the streptomycin-treated mouse intestine [28], and the study proposed that the BLI system offers a simple and direct method to study in vitro and in vivo competition between mutants and parental strain. Furthermore, the streptomycin-treated mouse colonization model was previously used to investigate the role of other iron uptake systems (e.g. ferrous iron uptake [Feo] system) in E.