Enteropathogenic Escherichia coli O111ab:H2 penetrates the small bowel epithelium in an infant with acute diarrhoea

Persistent diarrhea: still a serious public health problem in developing countries

Diarrhea is still responsible for high rates of morbidity and mortality in children under 5 years of age. The prolongation of the acute episode may cause digestive and absorptive malfunction and, consequently, malnutrition, raising the risk of death. The objective of this review is to supply the most recent knowledge in the field of persistent diarrhea and to contribute to the decrease of its incidence. Some possible etiologic agents may be involved, including viruses, bacteria, and parasites. Treatment must be addressed to avoid malabsorption of the nutrients of the diet, associated with replacement of the hydroelectrolytic losses, to prevent its prolongation. In the great majority of the episodes, antibiotics are not indicated. Breastfeeding, introduction of safe dietary strategies to prevent protein-energy malnutrition, and improvement of sanitary conditions and hygiene are measures to be promoted with the objective of decreasing the morbidity/mortality of the diarrheic disease in children less than 5 years of age.

In vitro evolution of an archetypal enteropathogenic Escherichia coli strain

Enteropathogenic Escherichia coli (EPEC) is a leading cause of infantile diarrhea in developing countries. EPEC strain E2348/69 is used worldwide as a prototype to study EPEC genetics and disease. However, isolates of E2348/69 differ phenotypically, reflecting a history of in vitro selection. To identify the genomic and phenotypic changes in the prototype strain, we sequenced the genome of the nalidixic acid-resistant (Nal(r)) E2348/69 clone. We also sequenced a recent nleF mutant derived by one-step PCR mutagenesis from the Nal(r) strain. The sequencing results revealed no unintended changes between the mutant and the parent strain. However, loss of the pE2348-2 plasmid and 3 nonsynonymous mutations were found in comparison to the published streptomycin-resistant (Str(r)) E2348/69 reference genome. One mutation is a conservative amino acid substitution in ftsK. Another, in gyrA, is a mutation known to result in resistance to nalidixic acid. The third mutation converts a stop codon to a tryptophan, predicted to result in the fusion of hflD, the lysogenization regulator, to purB. The purB gene encodes an adenylosuccinate lyase involved in purine biosynthesis. The Nal(r) clone has a lower growth rate than the Str(r) isolate when cultured in minimal media, a difference which is corrected upon addition of adenine or by genetic complementation with purB. Addition of adenine or genetic complementation also restored the invasion efficiency of the Nal(r) clone. This report reconciles longstanding inconsistencies in phenotypic properties of an archetypal strain and provides both reassurance and cautions regarding intentional and unintentional evolution in vitro.

Attaching-effacing bacteria in animals

Enteric bacteria with a demonstrable or potential ability to form attaching-effacing lesions, so-called attaching-effacing (AE) bacteria, have been found in the intestinal tracts of a wide variety of warm-blooded animal species, including man. In some host species, for example cattle, pigs, rabbits and human beings, attaching-effacing Escherichia coli (AEEC) have an established role as enteropathogens. In other host species, AE bacteria are of less certain significance. With continuing advances in the detection and typing of AE strains, the importance of these bacteria for many hosts is likely to become clearer. The pathogenic effects of AE bacteria result from adhesion to the intestinal mucosa by a variety of mechanisms, culminating in the formation of the characteristic intimate adhesion of the AE lesion. The ability to induce AE lesions is mediated by the co-ordinated expression of some 40 bacterial genes organized within a so-called pathogenicity island, known as the "Locus for Enterocyte Effacement". It is also believed that the production of bacterial toxins, principally Vero toxins, is a significant virulence factor for some AEEC strains. Recent areas of research into AE bacteria include: the use of Citrobacter rodentium to model human AEEC disease; quorum-sensing mechanisms used by AEEC to modulate virulence gene expression; and the potential role of adhesion in the persistent colonization of the intestine by AE bacteria. This review of AE bacteria covers their molecular biology, their occurrence in various animal species, and the diagnosis, pathology and clinical aspects of animal diseases with which they are associated. Reference is made to human pathogens where appropriate. The focus is mainly on natural colonization and disease, but complementary experimental data are also included.

Saccharomyces boulardii preserves the barrier function and modulates the signal transduction pathway induced in enteropathogenic Escherichia coli-infected T84 cells

Use of the nonpathogenic yeast Saccharomyces boulardii in the treatment of infectious diarrhea has attracted growing interest. The present study designed to investigate the effect of this yeast on enteropathogenic Escherichia coli (EPEC)-associated disease demonstrates that S. boulardii abrogated the alterations induced by an EPEC strain on transepithelial resistance, [(3)H]inulin flux, and ZO-1 distribution in T84 cells. Moreover, EPEC-mediated apoptosis of epithelial cells was delayed in the presence of S. boulardii. The yeast did not modify the number of adherent bacteria but lowered by 50% the number of intracellular bacteria. Infection by EPEC induced tyrosine phosphorylation of several proteins in T84 cells, including p46 and p52 SHC isoforms, that was attenuated in the presence of S. boulardii. Similarly, EPEC-induced activation of the ERK1/2 mitogen-activated protein (MAP) kinase pathway was diminished in the presence of the yeast. Interestingly, inhibition of the ERK1/2 pathway with the specific inhibitor PD 98059 decreased EPEC internalization, suggesting that modulation of the ERK1/2 MAP pathway might account for the lowering of the number of intracellular bacteria observed in the presence of S. boulardii. Altogether, this study demonstrated that S. boulardii exerts a protective effect on epithelial cells after EPEC adhesion by modulating the signaling pathway induced by bacterial infection.

Citrobacter rodentium infection in mice elicits a mucosal Th1 cytokine response and lesions similar to those in murine inflammatory bowel disease

Citrobacter rodentium is a classically noninvasive pathogen of mice that is similar to enteropathogenic Escherichia coli (EPEC) in man. Following oral infection of young mice, the organism colonizes the distal colon, and within 1 week the colonic mucosa doubles in thickness and there is massive epithelial cell hyperplasia. Since T-cell responses in mouse models of inflammatory bowel disease (IBD) also cause epithelial hyperplasia, we have investigated the possibility that C. rodentium promotes similar T-cell responses in the mucosa, thereby increasing epithelial shedding, transmission, and replication of the organism. Beginning 6 days after infection, bacteria were observed to be in close association with the epithelial surface and were also visible scattered throughout the lamina propria and in the submucosa. There was a CD3(+)-cell infiltrate into the colonic lamina propria and epithelium as well as mucosal thickening and crypt hyperplasia. The majority of CD3(+) cells were CD4(+) and were not gammadelta+. Reverse transcription-PCR analysis of cytokines also revealed a highly polarized Th1 response (interleukin-12, gamma interferon, and tumor necrosis factor alpha) in the mucosa and a large increase in the epithelial cell mitogen keratinocyte growth factor. None of the changes were seen in mice inoculated with bacteria lacking intimin (which is necessary for colonization), but they were seen in mice inoculated with C. rodentium complemented with intimin from EPEC. This is the first example of a classically noninvasive bacterial pathogen which elicits a strong mucosal Th1 response and which produces pathology similar to that seen in mouse models of IBD, which is also characterized by a strong Th1 response. These results also suggest that the colonic mucosa responds in a stereotypic way to Th1 responses.

Generation of Escherichia coli intimin derivatives with differing biological activities using site-directed mutagenesis of the intimin C-terminus domain

Intimins, encoded by eae genes, are outer membrane proteins involved in attaching-effacing (A/E) lesion formation and host cell invasion by pathogenic bacteria, including enteropathogenic Escherichia coli (EPEC) and Citrobacter rodentium. A series of intimins, harbouring specific mutations close to the C-terminus, were constructed using pCVD438, which encodes the eae gene from EPEC strain E2348/69. These mutant plasmids were introduced into EPEC strain CVD206 and C. rodentium strain DBS255, which both contain deletion mutations in their eae genes. CVD206, CVD206(pCVD438) and CVD206(pCVD438) derivatives were assessed for their ability to promote A/E lesion formation or invasion of HEp-2 cells and to induce A/E lesions on fresh human intestinal in vitro organ cultures (IVOC). The pathogenicity of C. rodentium DBS255 harbouring these plasmid derivatives was also studied in mice. Here, we report that intimin-mediated A/E lesion formation can be segregated from intimin-mediated HEp-2 cell invasion. Moreover, adherence to IVOC, EPEC-induced microvillus elongation and colonization of the murine intestine by C. rodentium were also modulated by the modified intimins.

Mechanisms of gut damage by Escherichia coli

This chapter primarily concerns three main categories of diarrhoeagenic Escherichia coli, enteropathogenic (EPEC), enterohaemorrhagic (EHEC) and enteroaggregative (EAEC) E. coli. They have distinctive virulence factors and vary in the enteropathies they produce. The molecular biological approach has opened up the complex way in which they interact with the intestine. EPEC and EHEC show a subversive approach to colonization in that they adapt the host cell to their requirements in the formation of the attaching effacing lesion. EAEC appear to co-opt the host defence system to produce a biofilm-like colony and currently go unrecognized in routine laboratories.

Attaching and effacing enteropathogenic Escherichia coli O18ab invades epithelial cells and causes persistent diarrhea

A case of persistent diarrhea following Escherichia coli O18ab gastroenteritis is reported. Electron microscopy of a biopsy of the small intestine showed effacement of the brush border, attachment of bacteria to the epithelial cells with pedestal formation, and bacteria within the enterocytes. The bacterial isolate was an enteropathogenic E. coli isolate which did not contain the adherence factor (EAF) but possessed the attaching-effacing eae gene, was able to invade HeLa cells in a gentamicin invasion assay, and also invaded rabbit intestinal cells. Results suggest that E. coli organisms of the O18ab serotype may cause diarrhea by an as yet unknown pathogenic mechanism, involving attaching to and effacing of enterocytes followed by invasion of the epithelial cells.

The cell-binding domain of intimin from enteropathogenic Escherichia coli binds to beta1 integrins

Bacteria interact with mammalian cells surface molecules, such as integrins, to colonize tissues and evade immunological detection. Herein, the ability of intimin, an outer membrane protein from enteropathogenic Escherichia coli, to bind beta1 integrins was investigated. Solid-phase binding assays revealed binding of the carboxyl-terminal 280 amino acids of intimin (Int280) to alpha4beta1 and alpha5beta1 integrins. The binding required divalent ions (in particular, it was enhanced by Mn2+) and was inhibited by an RGD-containing peptide. Nonderivatized Int280, but not Int280CS (like Int280 but with Cys-937 replaced by Ser) blocked the binding of biotinylated Int280 to integrins. Int280 did not efficiently inhibit beta1 integrin binding of invasin from Yersinia pseudotuberculosis. Both intimin and invasin, immobilized on plastic surfaces, mediated adherence of resting or phorbol 12-myristate 13-acetate-activated human CD4(+) T cells, whereas fibronectin mediated the adherence of only activated T cells. T cell binding to intimin and invasin was integrin mediated because it was specifically blocked by an RGD-containing peptide and by antibodies directed against the integrin subunits beta1, alpha4, and alpha5. These results demonstrate a specific integrin binding activity for intimin that is related to, but distinct from, that of invasin.

Royal Society of Tropical Medicine and Hygiene meeting at Manson House, London, 14 December 1995. Enteropathogenic Escherichia coli--mucosal infection models

The formation of attaching and effacing (A/E) lesions is central to the pathogenesis of enteropathogenic Escherichia coli (EPEC)-mediated disease in humans and Citrobacter rodentium-mediated transmissible colonic hyperplasia in mice. Closely related outer membrane proteins, known as intimins, are required for formation of the A/E lesion by both EPEC and C. rodentium. In this study we found similar ultrastructural damage in small intestinal biopsies from an EPEC-infected child and large bowel specimens from C. rodentium-infected mice. The C. rodentium-infected large bowel biopsies revealed massive hyperplastic reactions and the infected human small intestinal biopsies showed an increase in total crypt cell number and mitotic index. EPEC-infected small intestinal organ cultures revealed bacteria adhering in a localized pattern and evidence of A/E lesions. Covaspheres coated with a biologically active cell-binding domain of intimin also adhered to cells in a localized fashion but did not induce the characteristic A/E lesions.

Concomitant bacteraemia as a risk factor for diarrhoeal disease mortality in Karachi: a case-control study of hospitalized children

The objective of this study was to evaluate risk factors for death due to diarrhoea among hospitalized children at the Aga Khan University Hospital (AKUH), Karachi. We conducted a retrospective case-control study of all diarrhoea deaths at AKUH over the period 1988-93. For each death, the next two consecutive admissions matched for gender and type of diarrhoea were identified as controls. Data were analysed by univariate methods and logistic regression analysis. A total of 42 deaths and 84 matched controls were identified. Blood cultures at admission were obtained in all deaths and 94% of controls. The rates of isolation of organisms from blood cultures were significantly higher among deaths [38 versus 9%, odds ratio (OR) 6.5, 95% confidence interval (CI) 2.2-19.9], the majority of which were Gram-negative Enterobacteriaceae (94 versus 57%, Fisher's exact test p < 0.02). Conditional logistic regression revealed that several clinical and laboratory features of systemic infection were associated with a significantly increased risk of mortality, such as anorexia (OR 3.9, 95% CI 1.4-10.9), drowsiness (OR 4.4, 95% CI 1.3-15.3), respiratory distress (OR 7.0, 95% CI 1.4 36.6), anaemia (OR 5.8, 95% CI 2.0-16.6) and a positive blood culture (OR 8.7, 95% CI 2.5-30.7). Our data suggest that bacteraemia with Enterobacteriaceae is common among hospitalized malnourished children with diarrhoea and systemic infection may be an important risk factor for mortality.