Enterotoxigenic Escherichia coli - an overview

Abstract

Enterotoxigenic Escherichia coli is an important cause of traveler's diarrhea and diarrheal illnesses in children in the developing world. In this presentation we will focus on the main virulence attributes of this pathogenic category of E. coli, and discuss the evolution of studies conducted in our laboratory. The importance of ETEC as a major cause of diarrhea was recognized in the late 60's. Since then, a large body of information on the epidemiology and pathogenesis of this group of bacteria has been accumulated.ETEC strains are a worldwide cause of acute diarrheal disease in both human and animals, responsible for a high rate of infantile mortality in the developing countries. They are also an important agent of diarrhea among travelers from industrialized countries visiting tropical or subtropical areas of the world.Two virulence attributes that characterize ETEC are the colonization of the small intestine surface and the production of enterotoxins that induce a net secretion of electrolytes and water into the gut lumen.The enterotoxins produced by these organisms belong to two major classes of heat-labile and heatstable toxins (LT and ST, respectively), that differed in regard to structure, antigenicity and mechanisms of action, usually related to cyclic nucleotides (Acheson 1992, Spangler 1992, Sears & Kaper 1996. LT, which is closely related to cholera toxin (CT), is an oligomeric protein of 85 kDa composed by five identical B subunits, arranged in a ring and in one A subunit. The B subunits bind strongly to the intestinal receptor GM1, while the A subunit is responsible for the enzymatic activity of the toxin, and is proteolitically cleaved to yield A 1 and A 2 peptides joined by a disulfide bond. After binding to the host cell membranes, LT enters into the cell through an endocytic process and the A 1 peptide ADP-ribosylates the alpha subunit of the GTPbinding protein Gs, leading to activation of adenylate cyclase in the enterocyte and accumulation of cyclic AMP. The intracellular accumulation of cAMP elicits secretion by crypt cells and decrease absorption by villus tip cells. In this family of toxins two distinct classes were described LT-I and LT-II, that although very similar present some differences specially in the B subunit.In contrast to LTs, the STs are small, monomeric toxins of approximately 5 kDa, and two different classes were also distinguished based on biological and chemical properties: ST-I and ST-II. ST-I is methanol soluble and active in the infant mouse model, and differences in the aminoacid sequence of the toxin led to the identification of two genetic variants ST-Ih and ST-Ip, described initially in association with strains isolated from humans and pigs, respectively. However, subsequent studies showed that both variants can be produced by human ETEC strains, although ST-Ih seems to prevailed. ST-II, which is methanol insoluble and causes a positive response on pig and rat intestinal loops, is associated primarily with diarrheal disease in pigs, but some human ETEC strains expre...

Genotypic and phenotypic characterization of enterotoxigenicEscherichia coli(ETEC) strains isolated in Rio de Janeiro city, Brazil

“…CF-negative ETEC strains corresponded to 63.6% of the isolates analyzed. Studies in di¡erent parts of the world have shown that a considerable number of strains do not possess any known CFs suggesting the presence of as yet undescribed ¢mbrial or a¢mbrial antigens [5,6,28]. The association of speci¢c O and H antigens with strains lacking a de¢ned CF has been already described [8] and, similarly to our results, mainly related to LT strains.…”

“…Although a small number of isolates was included in the present investigation, they comprised all the ETEC recovered during a previous investigation on the occurrence of the different categories of DEC in children, representing 12.7% of the DEC isolates [20]. The results indicate that the ETEC isolates in this particular study exhibited a wide range of phenotypic and genotypic characteristics, which in some cases, were distinct from those of isolates recovered in other Brazilian locations [6,39]. This information is of special value since the available data on ETEC infections in the studied community remains scarce.…”

“…Enterotoxigenic Escherichia coli (ETEC) strains are an important worldwide cause of diarrheal disease in humans, affecting especially children in developing areas and visitors from developed countries [1–4]. Two major virulence determinants have been identified in ETEC strains: enterotoxins and colonization factors antigens (CFAs), which are often encoded by plasmids that also encode heat‐stable (ST) and/or heat‐labile (LT) enterotoxins [5,6]. Distinct types of CFAs have been described in human ETEC isolates and they are mainly constituted by protein fimbriae [7].…”

Critical Role of Zinc in a New Murine Model of Enterotoxigenic Escherichia coli Diarrhea

“…ETEC virulence is associated with colonization of the small intestine and production of one or more toxins that induce secretion of chloride, sodium, and water into the lumen ( 9 ). The two major classes of toxins, the heat-labile toxins (LT) and heat-stable toxins (ST), act by stimulating expression of adenylate and guanylate cyclase, respectively ( 10 , 11 ).…”

Detection of enterotoxigenic K99 (F5) and F41 from fecal sample of calves by molecular and serological methods

“…Two biological classes of enterotoxins, heat labile (LT) and heat stable (STa and STb), are produced by ETEC. Most bovine ETEC produce STa (Guth 2000).…”