The molecular basis for control of ETEC enterotoxin expression in response to environment and host.

James R J Haycocks,Joseph T Wade,Anne M Stringer,David C Grainger,Prateek Sharma,Frank R Deleo

doi:10.1371/journal.ppat.1004605

Abstract

Enterotoxigenic Escherichia coli (ETEC) cause severe diarrhoea in humans and neonatal farm animals. Annually, 380,000 human deaths, and multi-million dollar losses in the farming industry, can be attributed to ETEC infections. Illness results from the action of enterotoxins, which disrupt signalling pathways that manage water and electrolyte homeostasis in the mammalian gut. The resulting fluid loss is treated by oral rehydration. Hence, aqueous solutions of glucose and salt are ingested by the patient. Given the central role of enterotoxins in disease, we have characterised the regulatory trigger that controls toxin production. We show that, at the molecular level, the trigger is comprised of two gene regulatory proteins, CRP and H-NS. Strikingly, this renders toxin expression sensitive to both conditions encountered on host cell attachment and the components of oral rehydration therapy. For example, enterotoxin expression is induced by salt in an H-NS dependent manner. Furthermore, depending on the toxin gene, expression is activated or repressed by glucose. The precise sensitivity of the regulatory trigger to glucose differs because of variations in the regulatory setup for each toxin encoding gene.

Highlights

Enterotoxigenic Escherichia coli (ETEC) are Gram negative bacteria that cause severe diarrhoea, known as non-vibrio cholera, in humans [1,2]
In each plot genes are illustrated by blue lines, DNA G/C content by a cyan and pink graph, HNS binding is in green and cAMP receptor protein (CRP) binding is shown in orange
CRP binding occurs in expected locations; 96% of the CRP binding sites are associated with the DNA logo shown in Fig. 1B (i.e. the known CRP consensus sequence (13–15))

Summary

Introduction

ETEC are Gram negative bacteria that cause severe diarrhoea, known as non-vibrio cholera, in humans [1,2]. The heat-stable toxin (ST) mimics the human hormone guanylin [6]. Both toxins are secreted by ETEC during infection. LT binds to host cell GM1 gangliosides and is endocytosed [8,9]. This triggers constitutive cAMP production in the affected cell [8]. The ST toxin, encoded by the estA gene, interferes with cell signalling [6]. The combined actions of LT and ST cause loss of H2O, and electrolytes, from epithelial cells into the gut lumen [4]. Despite the existence of molecular mechanisms that allow bacteria to respond to these signals, the consequences for ETEC are unknown

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Discussion

Conclusion