Escherichia coli is the predominant nonpathogenic facultative flora of the human intestine. Some E. coli strains, however, have developed the ability to cause disease of the gastrointestinal, urinary, or central nervous system in even the most robust human hosts. Diarrheagenic strains of E. coli can be divided into at least six different categories with corresponding distinct pathogenic schemes. Taken together, these organisms probably represent the most common cause of pediatric diarrhea worldwide. Several distinct clinical syndromes accompany infection with diarrheagenic E. coli categories, including traveler’s diarrhea (enterotoxigenic E. coli), hemorrhagic colitis and hemolytic-uremic syndrome (enterohemorrhagic E. coli), persistent diarrhea (enteroaggregative E. coli), and watery diarrhea of infants (enteropathogenic E. coli). This review discusses the current level of understanding of the pathogenesis of the diarrheagenic E. coli strains and describes how their pathogenic schemes underlie the clinical manifestations, diagnostic approach, and epidemiologic investigation of these important pathogens.

Diarrheagenic Escherichia coli

https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(05)71144-2.pdf

Shiga-toxin-producing Escherichia coli and haemolytic uraemic syndrome

Since their initial recognition 20 years ago, Shiga toxin-producing Escherichia coli (STEC) strains have emerged as an important cause of serious human gastrointestinal disease, which may result in life-threatening complications such as hemolytic-uremic syndrome. Food-borne outbreaks of STEC disease appear to be increasing and, when mass-produced and mass-distributed foods are concerned, can involve large numbers of people. Development of therapeutic and preventative strategies to combat STEC disease requires a thorough understanding of the mechanisms by which STEC organisms colonize the human intestinal tract and cause local and systemic pathological changes. While our knowledge remains incomplete, recent studies have improved our understanding of these processes, particularly the complex interaction between Shiga toxins and host cells, which is central to the pathogenesis of STEC disease. In addition, several putative accessory virulence factors have been identified and partly characterized. The capacity to limit the scale and severity of STEC disease is also dependent upon rapid and sensitive diagnostic procedures for analysis of human samples and suspect vehicles. The increased application of advanced molecular technologies in clinical laboratories has significantly improved our capacity to diagnose STEC infection early in the course of disease and to detect low levels of environmental contamination. This, in turn, has created a potential window of opportunity for future therapeutic intervention.

Pathogenesis and Diagnosis of Shiga Toxin-Producing Escherichia coli Infections

Verocytotoxin (VT)-producing Escherichia coli (VTEC) are a newly recognized group of enteric pathogens which are increasingly being recognized as common causes of diarrhea in some geographic settings. Outbreak studies indicate that most patients with VTEC infection develop mild uncomplicated diarrhea. However, a significant risk of two serious and potentially life-threatening complications, hemorrhagic colitis and the hemolytic uremic syndrome, makes VTEC infection a public health problem of serious concern. The main reservoirs of VTEC appear to be the intestinal tracts of animals, and foods of animal (especially bovine) origin are probably the principal sources for human infection. The term VT refers to a family of subunit exotoxins with high biological activity. Individual VTEC strains elaborate one or both of at least two serologically distinct, bacteriophage-mediated VTs (VT1 and VT2) which are closely related to Shiga toxin and are thus also referred to as Shiga-like toxins. The holotoxins bind to cells, via their B subunits, to a specific receptor which is probably the glycolipid, globotriosyl ceramide (Gb3). Binding is followed by internalization of the A subunit, which, after it is proteolytically nicked and reduced to the A1 fragment, inhibits protein synthesis in mammalian cells by inactivating 60S ribosomal subunits through selective structural modification of 28S ribosomal ribonucleic acid. The mechanism of VTEC diarrhea is still controversial, and the relative roles of locally acting VT and "attaching and effacing adherence" of VTEC to the mucosa have yet to be resolved. There is increasing evidence that hemolytic uremic syndrome and possibly hemorrhagic colitis result from the systemic action of VT on vascular endothelial cells. The role of antitoxic immunity in preventing the systemic complications of VTEC infection is being explored. Antibiotics appear to be contraindicated in the treatment of VTEC infection. The most common VTEC serotype associated with human disease is O157:H7, but over 50 different VT-positive O:H serotypes have now been identified. The best strategies for diagnosing human VTEC infection include testing for the presence of free VT in fecal filtrates and examining fecal cultures for VTEC by means of deoxyribonucleic acid probes that specify genes encoding VT1 and VT2. Both methods are currently confined to specialized laboratories and await commercial development for wider use. In the meantime, most laboratories should continue to screen for the most common human VTEC serotype, O157:H7, using a sorbitol-containing MacConkey medium.

Infection by verocytotoxin-producing Escherichia coli.

Forty pediatric patients with idiopathic hemolytic uremic syndrome (HUS) were investigated for evidence of infection by Verotoxin-producing Escherichia coli (VTEC). Fecal VTEC (belonging to at least six different O serogroups including O26, O111, O113, O121, O145, and O157) or specifically neutralizable free-fecal Verotoxin (VT) or both were detected in 24 (60%) patients but were not detected in 40 matched controls. Ten of 15 of the former developed fourfold or greater rises in VT-neutralizing antibody titers, as did six other patients who were negative for both fecal VTEC and VT. A total of 30 (75%) patients had evidence of VTEC infection by one or more criteria. We concluded that a significant association exists between idiopathic HUS and infection by VTEC. The detection of free-fecal VT was the most important procedure for the early diagnosis of this infection because, in our study, VTEC were never isolated in the absence of fecal VT, whereas fecal VT was often present even when VTEC were undetectable.

The Association Between Idiopathic Hemolytic Uremic Syndrome and Infection by Verotoxin-Producing Escherichia coli

A cytotoxin was found in culture filtrates of a number of Escherichia coli strains that differed from the known heat-stable and heat-labile enterotoxins of E. coli. It was cytotoxic for Vero but not for Y-1 or CHO cells, and its effect on Vero was distinctly different from that of heat-labile enterotoxin. It was labile to heat and antigenically different from heat-labile enterotoxin, and membrane filtration indicated a molecular weight of 10,000 to 30,000.

Vero response to a cytotoxin of Escherichia coli.

The continuous cell line of African green monkey kidney, Vero, showed characteristic morphological changes in response to culture filtrates from toxigenic strains of Escherichia coli. The response compared favorably with that of Y-1 (mouse adrenal) and CHO (Chinese hamster ovary) cells. Vero cells were the simplest and most economical to maintain in the laboratory.

https://iai.asm.org/content/iai/16/2/617.full.pdf

Assay of Escherichia coli heat-labile enterotoxin with vero cells

Isoelectric focusing of a heat-labile cytotoxin of Escherichia coli H30 revealed the presence of two molecular variants, pI 7.2 and a comparatively small quantity of pI 6.8. Predominant component pI 7.2 had a molecular weight of 28,000, induced some fluid accumulation in rabbit ileal loops, and showed no morphological response in Y-1 cells but a strong cytotoxic effect on Vero cells.

Properties of an Escherichia coli cytotoxin.

Five heat-labile, partially purified toxic products of Escherichia coli were distinguished by isoelectric focusing, molecular weight, and neutralization with homologous and heterologous antisera. Only two affected the morphology of Y-1 cells, induced fluid accumulation in rabbit ileal loops, and stimulated production of cyclic AMP in Vero cells; these two did not cross-neutralize and only one showed cross-neutralization with cholera antitoxin. The remaining three products were cytotoxic for Vero cells.

Comparative studies of five heat-labile toxic products of Escherichia coli.

The morphological response of Vero cells to Escherichia coli heat-labile enterotoxin was similar to that of cholera toxin and was accompanied by increases in the intracellular level of cyclic AMP. The effects of both enterotoxins were enhanced by the presence of phosphodiesterase inhibitor and inhibited by heat or specific antisera. Accumulation of cyclic AMP preceded the morphological response.

J I Speirs

Papers

Vero response to a cytotoxin of Escherichia coli.

Assay of Escherichia coli heat-labile enterotoxin with vero cells

Properties of an Escherichia coli cytotoxin.

Comparative studies of five heat-labile toxic products of Escherichia coli.

Stimulation of cyclic AMP secretion in Vero cells by enterotoxins of Escherichia coli and Vibrio cholerae.