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Proc Natl Acad Sci U S A. 2018 Sep 18;115(38):E8968-E8976. doi: 10.1073/pnas.1808982115. Epub 2018 Aug 20.

Enterotoxigenic E. coli virulence gene regulation in human infections.

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Department of Molecular Biosciences, The University of Texas at Austin, Austin, TX 78712.
Enteric Diseases Department, Naval Medical Research Center, Silver Spring, MD 20910.
Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205.
Immunology, Henry M. Jackson Foundation for the Advancement of Military Medicine, Bethesda, MD 20817.
Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814.
Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA 30602;
Center of Vaccines and Immunology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602.
Department of Microbiology, College of Arts and Sciences, University of Georgia, Athens, GA 30602.


Enterotoxigenic Escherichia coli (ETEC) is a global diarrheal pathogen that utilizes adhesins and secreted enterotoxins to cause disease in mammalian hosts. Decades of research on virulence factor regulation in ETEC has revealed a variety of environmental factors that influence gene expression, including bile, pH, bicarbonate, osmolarity, and glucose. However, other hallmarks of the intestinal tract, such as low oxygen availability, have not been examined. Further, determining how ETEC integrates these signals in the complex host environment is challenging. To address this, we characterized ETEC's response to the human host using samples from a controlled human infection model. We found ETEC senses environmental oxygen to globally influence virulence factor expression via the oxygen-sensitive transcriptional regulator fumarate and nitrate reduction (FNR) regulator. In vitro anaerobic growth replicates the in vivo virulence factor expression profile, and deletion of fnr in ETEC strain H10407 results in a significant increase in expression of all classical virulence factors, including the colonization factor antigen I (CFA/I) adhesin operon and both heat-stable and heat-labile enterotoxins. These data depict a model of ETEC infection where FNR activity can globally influence virulence gene expression, and therefore proximity to the oxygenated zone bordering intestinal epithelial cells likely influences ETEC virulence gene expression in vivo. Outside of the host, ETEC biofilms are associated with seasonal ETEC epidemics, and we find FNR is a regulator of biofilm production. Together these data suggest FNR-dependent oxygen sensing in ETEC has implications for human infection inside and outside of the host.


ETEC; FNR; cfa; enterotoxigenic E. coli; toxin

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[Available on 2019-03-18]
[Indexed for MEDLINE]

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