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Abstract
BackgroundA major outbreak of bloody diarrhea associated with Shiga toxin-producing Escherichia coli O104:H4 occurred early in 2011, to which an unusual number of hemolytic uremic syndrome cases were linked. Due to limited information regarding pathogenesis and/or virulence properties of this particular serotype, we investigated the contribution of the aerobactin iron transport system during in vitro and in vivo conditions.ResultsA bioluminescent reporter construct was used to perform real-time monitoring of E. coli O104:H4 in a mouse model of infection. We verified that our reporter strain maintained characteristics and growth kinetics that were similar to those of the wild-type E. coli strain. We found that the intestinal cecum of ICR (CD-1) mice was colonized by O104:H4, with bacteria persisting for up to 7 days after intragastric inoculation. MALDI-TOF analysis of heat-extracted proteins was performed to identify putative surface-exposed virulence determinants. A protein with a high similarity to the aerobactin iron receptor was identified and further demonstrated to be up-regulated in E. coli O104:H4 when grown on MacConkey agar or during iron-depleted conditions. Because the aerobactin iron acquisition system is a key virulence factor in Enterobacteriaceae, an isogenic aerobactin receptor (iutA) mutant was created and its intestinal fitness assessed in the murine model. We demonstrated that the aerobactin mutant was out-competed by the wild-type E. coli O104:H4 during in vivo competition experiments, and the mutant was unable to persist in the cecum.ConclusionOur findings demonstrate that bioluminescent imaging is a useful tool to monitor E. coli O104:H4 colonization properties, and the murine model can become a rapid way to evaluate bacterial factors associated with fitness and/or colonization during E. coli O104:H4 infections.
Highlights
A major outbreak of bloody diarrhea associated with Shiga toxin-producing Escherichia coli O104:H4 occurred early in 2011, to which an unusual number of hemolytic uremic syndrome cases were linked
Shiga toxin-producing Escherichia coli (STEC) are members of a category of pathogenic E. coli that can cause illness ranging from mild intestinal diarrheal disease to severe kidney complications, such as hemolytic uremic syndrome (HUS; reviewed in [1])
The outbreak was originally thought to have been caused by a STEC strain, but was later shown to be produced as a result of an enteroaggregative E. coli (EAEC) strain that had acquired the genes for production of Shiga toxins [6,7,8,9]
Summary
A major outbreak of bloody diarrhea associated with Shiga toxin-producing Escherichia coli O104:H4 occurred early in 2011, to which an unusual number of hemolytic uremic syndrome cases were linked. Shiga toxin-producing Escherichia coli (STEC) are members of a category of pathogenic E. coli that can cause illness ranging from mild intestinal diarrheal disease to severe kidney complications, such as hemolytic uremic syndrome (HUS; reviewed in [1]). In 2011, an uncommon strain of pathogenic E. coli serotype O104:H4 caused an unusual number of gastroenteritis and HUS cases, occurring predominantly in adults. The outbreak was originally thought to have been caused by a STEC strain, but was later shown to be produced as a result of an enteroaggregative E. coli (EAEC) strain that had acquired the genes for production of Shiga toxins [6,7,8,9]
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