(422a) Interkingdom Signaling In E. Coli O157:H7 Infections

The gastrointestinal tract accounts for 30 - 50% of the total neuroendocrine molecules (hormones) produced in the human body. Hormones synthesized in the gut through the enteric nervous system include norepinephrine (Norepi), dopamine, and serotonin. Bacteria, both non-pathogenic microflora residing in the gut as well as entering pathogenic bacteria entering the GI tract, are routinely exposed to these molecules. Therefore, it is not surprising that these bacteria have evolved to recognize the different eukaryotic signals. Indeed, prior studies have shown that norepinephrine can increase the growth rate of the pathogen E. coli O157:H7 (EHEC), as well as up-regulate expression of genes involved in infection. In addition to the hormones, bacteria are also routinely exposed to different prokaryotic signals such as the quorum sensing molecules autoinducer-2 (AI-2) and AI-3, and other stationary phase molecules like indole and its derivatives. Given that bacteria are exposed to and recognize a broad spectrum of molecules, it has been proposed that bacterial colonization of the GI tract (which leads to infections) is the result of both intra-kingdom (i.e., signaling in response to prokaryotic molecules) and inter-kingdom (i.e., signaling initiated by eukaryotic hormones) signaling.

Here, we present the first report of systems-level signaling interaction framework in EHEC infections. We show using a novel two-fluorophore chemotaxis assay that EHEC demonstrates chemotactic migration towards epinephrine (Epi), norepinephrine, and AI-2 while indole repels this pathogen. In addition, the chemo-attractant molecules also resulted in statistically significant increase in phenotypes related to chemotaxis such as motility and biofilm formation, while indole attenuated these phenotypes. The molecular basis underlying the divergent regulation of EHEC infection by eukaryotic and prokaryotic signals was investigated using DNA microarrays. The expression of fifteen genes, including those involved in surface colonization and infection, was divergent in presence of epi/norepi as compared to indole (i.e., genes up-regulated by epi/norepi were down-regulated by indole, and vice-versa). An in vitro adhesion assay was also used to demonstrate that the changes in EHEC chemotaxis, motility, and biofilm formation are mirrored in the extent of adherence to HeLa cells (i.e., infection). In summary, we have presented five independent lines of evidence that strongly that EHEC utilizes inter-kingdom signaling through recognition of epi/norepi during infection, while intra-kingdom signaling through indole decreases the extent of infection. Based on these results, we propose a hypothetical model for describing EHEC colonization and infection in the context of intra- and inter-kingdom signaling.