Molecular mechanisms of enterotoxigenic Escherichia coli infection

Methionine deficiency reduces autophagy and accelerates death in intestinal epithelial cells infected with enterotoxigenic Escherichia coli

Infections by enterotoxigenic Escherichia coli (ETEC) result in large economic losses to the swine industry worldwide. Dietary supplementation with amino acids has been considered as a potential mechanism to improve host defenses against infection. The goal of this study was to determine whether methionine deprivation alters ETEC interactions with porcine intestinal epithelial cells. IPEC-1 cells were cultured in media with or without L-methionine. Methionine deprivation resulted in enhanced ETEC adhesion and increased both the cytotoxicity and apoptotic responses of IPEC-1 cells infected with ETEC. Methionine deprivation inhibited IPEC-1 cell autophagic responses, suggesting that the increased cytotoxicity of ETEC to methionine-deprived IPEC-1 cells might be due to defects in autophagy.

Draft Genome Sequence of Enterotoxigenic Escherichia coli Strain W25K

Enterotoxigenic Escherichia coli (ETEC) is a major cause of diarrheal disease in humans and newly weaned pigs. Here, we report the draft genome sequence of ETEC strain W25K, which causes diarrhea in piglets.

Contribution of the highly conserved EaeH surface protein to enterotoxigenic Escherichia coli pathogenesis

Enterotoxigenic Escherichia coli (ETEC) strains are among the most common causes of diarrheal illness worldwide. These pathogens disproportionately afflict children in developing countries, where they cause substantial morbidity and are responsible for hundreds of thousands of deaths each year. Although these organisms are important targets for enteric vaccines, most development efforts to date have centered on a subset of plasmid-encoded fimbrial adhesins known as colonization factors and heat-labile toxin (LT). Emerging data suggest that ETEC undergoes considerable changes in its surface architecture, sequentially deploying a number of putative adhesins during its interactions with the host. We demonstrate here that one putative highly conserved, chromosomally encoded adhesin, EaeH, engages the surfaces of intestinal epithelial cells and contributes to bacterial adhesion, LT delivery, and colonization of the small intestine.

Novel antigens for enterotoxigenic Escherichia coli vaccines

Enterotoxigenic Escherichia coli (ETEC) are the most common bacterial pathogens causing diarrhea in developing countries where they lead to hundreds of thousands of deaths, mostly in children. These organisms are a leading cause of diarrheal illness in travelers to endemic countries. ETEC pathogenesis, and consequently vaccine approaches, have largely focused on plasmid-encoded enterotoxins or fimbrial colonization factors. To date these approaches have not yielded a broadly protective vaccine. However, recent studies suggest that ETEC pathogenesis is more complex than previously appreciated and involves additional plasmid and chromosomally encoded virulence molecules that can be targeted in vaccines. Here, we review recent novel antigen discovery efforts, potential contribution of these proteins to the molecular pathogenesis of ETEC and protective immunity, and the potential implications for development of next generation vaccines for important pathogens. These proteins may help to improve the effectiveness of future vaccines by making them simpler and possibly broadly protective because of their conserved nature.

Phenotypic and genotypic characterization of enterotoxigenic Escherichia coli clinical isolates from northern Colombia, South America

Enterotoxigenic Escherichia coli (ETEC) are major causes of childhood diarrhea in low and middle income countries including Colombia, South America. To understand the diversity of ETEC strains in the region, clinical isolates obtained from northern Colombia children were evaluated for multiple locus sequencing typing, serotyping, classical and nonclassical virulence genes, and antibiotic susceptibility. Among 40 ETEC clinical isolates evaluated, 21 (52.5%) were positive for LT gene, 13 (32.5%) for ST gene, and 6 (15%) for both ST and LT. The most prevalent colonization surface antigens (CS) were CS21 and CFA/I identified in 21 (50%) and 13 (32.5%) isolates, respectively. The eatA, irp2, and fyuA were the most common nonclassical virulence genes present in more than 60% of the isolates. Ampicillin resistance (80% of the strains) was the most frequent phenotype among ETEC strains followed by trimethoprim-sulfamethoxazole resistance (52.5%). Based on multiple locus sequencing typing (MLST), we recognize that 6 clonal groups of ETEC clinical isolates circulate in Colombia. ETEC clinical isolates from children in northern Colombia are highly diverse, yet some isolates circulating in the community belong to well-defined clonal groups that share a unique set of virulence factors, serotypes, and MLST sequence types.

Genome Sequence of Enterotoxigenic Escherichia coli Strain B2C

Enterotoxigenic Escherichia coli (ETEC) is a major cause of diarrheal disease around the globe, causing an estimated 380,000 deaths annually. The disease is caused by a wide variety of strains. Here, we report the genome sequence of ETEC strain B2C, which was isolated from an American soldier in Vietnam.

Pathogenesis of human enterovirulent bacteria: lessons from cultured, fully differentiated human colon cancer cell lines

Hosts are protected from attack by potentially harmful enteric microorganisms, viruses, and parasites by the polarized fully differentiated epithelial cells that make up the epithelium, providing a physical and functional barrier. Enterovirulent bacteria interact with the epithelial polarized cells lining the intestinal barrier, and some invade the cells. A better understanding of the cross talk between enterovirulent bacteria and the polarized intestinal cells has resulted in the identification of essential enterovirulent bacterial structures and virulence gene products playing pivotal roles in pathogenesis. Cultured animal cell lines and cultured human nonintestinal, undifferentiated epithelial cells have been extensively used for understanding the mechanisms by which some human enterovirulent bacteria induce intestinal disorders. Human colon carcinoma cell lines which are able to express in culture the functional and structural characteristics of mature enterocytes and goblet cells have been established, mimicking structurally and functionally an intestinal epithelial barrier. Moreover, Caco-2-derived M-like cells have been established, mimicking the bacterial capture property of M cells of Peyer's patches. This review intends to analyze the cellular and molecular mechanisms of pathogenesis of human enterovirulent bacteria observed in infected cultured human colon carcinoma enterocyte-like HT-29 subpopulations, enterocyte-like Caco-2 and clone cells, the colonic T84 cell line, HT-29 mucus-secreting cell subpopulations, and Caco-2-derived M-like cells, including cell association, cell entry, intracellular lifestyle, structural lesions at the brush border, functional lesions in enterocytes and goblet cells, functional and structural lesions at the junctional domain, and host cellular defense responses.

Survey of antibiotic-resistant bacteria isolated from bottlenose dolphins Tursiops truncatus in the southeastern USA

Contamination of coastal waters can carry pathogens and contaminants that cause diseases in humans and wildlife, and these pathogens can be transported by water to areas where they are not indigenous. Marine mammals may be indicators of potential health effects from such pathogens and toxins. Here we isolated bacterial species of relevance to humans from wild bottlenose dolphins Tursiops truncatus and assayed isolated bacteria for antibiotic resistance. Samples were collected during capture-release dolphin health assessments at multiple coastal and estuarine sites along the US mid-Atlantic coast and the Gulf of Mexico. These samples were transported on ice and evaluated using commercial systems and aerobic culture techniques routinely employed in clinical laboratories. The most common bacteria identified were species belonging to the genus Vibrio, although Escherichia coli, Shewanella putrefaciens, and Pseudomonas fluorescens/putida were also common. Some of the bacterial species identified have been associated with human illness, including a strain of methicillin-resistant Staphylococcus aureus (MRSA) identified in 1 sample. Widespread antibiotic resistance was observed among all sites, although the percentage of resistant isolates varied across sites and across time. These data provide a baseline for future comparisons of the bacteria that colonize bottlenose dolphins in the southeastern USA.

Gut microbiome composition and function in experimental colitis during active disease and treatment-induced remission

Dysregulated immune responses to gut microbes are central to inflammatory bowel disease (IBD), and gut microbial activity can fuel chronic inflammation. Examining how IBD-directed therapies influence gut microbiomes may identify microbial community features integral to mitigating disease and maintaining health. However, IBD patients often receive multiple treatments during disease flares, confounding such analyses. Preclinical models of IBD with well-defined disease courses and opportunities for controlled treatment exposures provide a valuable solution. Here, we surveyed the gut microbiome of the T-bet(-/-) Rag2(-/-) mouse model of colitis during active disease and treatment-induced remission. Microbial features modified among these conditions included altered potential for carbohydrate and energy metabolism and bacterial pathogenesis, specifically cell motility and signal transduction pathways. We also observed an increased capacity for xenobiotics metabolism, including benzoate degradation, a pathway linking host adrenergic stress with enhanced bacterial virulence, and found decreased levels of fecal dopamine in active colitis. When transferred to gnotobiotic mice, gut microbiomes from mice with active disease versus treatment-induced remission elicited varying degrees of colitis. Thus, our study provides insight into specific microbial clades and pathways associated with health, active disease and treatment interventions in a mouse model of colitis.

Different assay conditions for detecting the production and release of heat-labile and heat-stable toxins in enterotoxigenic Escherichia coli isolates

Enterotoxigenic Escherichia coli (ETEC) produce heat-labile (LT) and/or heat-stable enterotoxins (ST). Despite that, the mechanism of action of both toxins are well known, there is great controversy in the literature concerning the in vitro production and release of LT and, for ST, no major concerns have been discussed. Furthermore, the majority of published papers describe the use of only one or a few ETEC isolates to define the production and release of these toxins, which hinders the detection of ETEC by phenotypic approaches. Thus, the present study was undertaken to obtain a better understanding of ST and LT toxin production and release under laboratory conditions. Accordingly, a collection of 90 LT-, ST-, and ST/LT-producing ETEC isolates was used to determine a protocol for toxin production and release aimed at ETEC detection. For this, we used previously raised anti-LT antibodies and the anti-ST monoclonal and polyclonal antibodies described herein. The presence of bile salts and the use of certain antibiotics improved ETEC toxin production/release. Triton X-100, as chemical treatment, proved to be an alternative method for toxin release. Consequently, a common protocol that can increase the production and release of LT and ST toxins could facilitate and enhance the sensitivity of diagnostic tests for ETEC using the raised and described antibodies in the present work.

Enterotoxigenic Escherichia coli secretes a highly conserved mucin-degrading metalloprotease to effectively engage intestinal epithelial cells

Enterotoxigenic Escherichia coli (ETEC) is a leading cause of death due to diarrheal illness among young children in developing countries, and there is currently no effective vaccine. Many elements of ETEC pathogenesis are still poorly defined. Here we demonstrate that YghJ, a secreted ETEC antigen identified in immunoproteomic studies using convalescent patient sera, is required for efficient access to small intestinal enterocytes and for the optimal delivery of heat-labile toxin (LT). Furthermore, YghJ is a highly conserved metalloprotease that influences intestinal colonization of ETEC by degrading the major mucins in the small intestine, MUC2 and MUC3. Genes encoding YghJ and its cognate type II secretion system (T2SS), which also secretes LT, are highly conserved in ETEC and exist in other enteric pathogens, including other diarrheagenic E. coli and Vibrio cholerae bacteria, suggesting that this mucin-degrading enzyme may represent a shared virulence feature of these important pathogens.

EatA, an immunogenic protective antigen of enterotoxigenic Escherichia coli, degrades intestinal mucin

Enterotoxigenic Escherichia coli (ETEC) is a major cause of morbidity and mortality due to infectious diarrhea in developing countries for which there is presently no effective vaccine. A central challenge in ETEC vaccinology has been the identification of conserved surface antigens to formulate a broadly protective vaccine. Here, we demonstrate that EatA, an immunogenic secreted serine protease of ETEC, contributes to virulence by degrading MUC2, the major protein present in the small intestinal mucous layer, and that removal of this barrier in vitro accelerates toxin access to the enterocyte surface. In addition, we demonstrate that vaccination with the recombinant secreted passenger domain of EatA (rEatAp) elicits high titers of antibody and is protective against intestinal infection with ETEC. These findings may have significant implications for development of both subunit and live-attenuated vaccines against ETEC and other enteric pathogens, including Shigella flexneri, that express similar proteins.

Development and accuracy of quantitative real-time polymerase chain reaction assays for detection and quantification of enterotoxigenic Escherichia coli (ETEC) heat labile and heat stable toxin genes in travelers' diarrhea samples

Enterotoxigenic Escherichia coli (ETEC), the leading bacterial pathogen of travelers' diarrhea, is routinely detected by an established DNA hybridization protocol that is neither sensitive nor quantitative. Quantitative real-time polymerase chain reaction (qPCR) assays that detect the ETEC toxin genes eltA, sta1, and sta2 in clinical stool samples were developed and tested using donor stool inoculated with known quantities of ETEC bacteria. The sensitivity of the qPCR assays is 89%, compared with 22% for the DNA hybridization assay, and the limits of detection are 10,000-fold lower than the DNA hybridization assays performed in parallel. Ninety-three clinical stool samples, previously characterized by DNA hybridization, were tested using the new ETEC qPCR assays. Discordant toxin profiles were observed for 22 samples, notably, four samples originally typed as ETEC negative were ETEC positive. The qPCR assays are unique in their sensitivity and ability to quantify the three toxin genes in clinical stool samples.

Enterotoxigenic Escherichia coli infection and intestinal thiamin uptake: studies with intestinal epithelial Caco-2 monolayers

Infections with enteric pathogens like enterotoxigenic Escherichia coli (ETEC) is a major health issue worldwide and while diarrhea is the major problem, prolonged, severe, and dual infections with multiple pathogens may also compromise the nutritional status of the infected individuals. There is almost nothing currently known about the effect of ETEC infection on intestinal absorptions of water-soluble vitamins including thiamin. We examined the effect of ETEC infection on intestinal uptake of the thiamin using as a model the human-derived intestinal epithelial Caco-2 cells. The results showed that infecting confluent Caco-2 monolayers with live ETEC (but not with boiled/killed ETEC or nonpathogenic E. coli) or treatment with bacterial culture supernatant led to a significant inhibition in thiamin uptake. This inhibition appears to be caused by a heat-labile and -secreted ETEC component and is mediated via activation of the epithelial adenylate cyclase system. The inhibition in thiamin uptake by ETEC was associated with a significant reduction in expression of human thiamin transporter-1 and -2 (hTHTR1 and hTHTR2) at the protein and mRNA levels as well as in the activity of the SLC19A2 and SLC19A3 promoters. Dual infection of Caco-2 cells with ETEC and EPEC (enteropathogenic E. coli) led to compounded inhibition in intestinal thiamin uptake. These results show for the first time that infection of human intestinal epithelial cells with ETEC causes a significant inhibition in intestinal thiamin uptake. This inhibition is mediated by a secreted heat-labile toxin and is associated with a decrease in the expression of intestinal thiamin transporters.

Enterotoxigenic Escherichia coli: Orchestrated host engagement

The enterotoxigenic Escherichia coli are a pervasive cause of serious diarrheal illness in developing countries. Presently, there is no vaccine to prevent these infections, and many features of the basic pathogenesis of these organisms remain poorly understood. Until very recently most pathogenesis studies had focused almost exclusively on a small subset of known "classical" virulence genes, namely fimbrial colonization factors and the heat-labile (LT) and heat stable (ST) enterotoxins. However, recent investigations of pathogen-host interactions reveal a surprisingly complex and intricately orchestrated engagement involving the interplay of classical and "novel" virulence genes, as well as participation of genes highly conserved in the E. coli species. These studies may inform further rational approaches to vaccine development for these important pathogens.

A dodecameric ring-like structure of the N0 domain of the type II secretin from enterotoxigenic Escherichia coli

In many bacteria, secretins from the type II secretion system (T2SS) function as outer membrane gated channels that enable passage of folded proteins from the periplasm into the extracellular milieu. Cryo-electron microscopy of the T2SS secretin GspD revealed previously the dodecameric cylindrical architecture of secretins, and crystal structures of periplasmic secretin domains showed a modular domain organization. However, no high-resolution experimental data has as yet been provided about how the entire T2SS secretin or its domains are organized in a cylindrical fashion. Here we present a crystal structure of the N0 domain of the T2SS secretin GspD from enterotoxigenic Escherichia coli containing a helix with 12 subunits per turn. The helix has an outer diameter of ∼125Å and a pitch of only 24Å which suggests a model of a cylindrical dodecameric N0 ring whose dimensions correspond with the cryo-electron microscopy map of Vibrio cholerae GspD. The N0 domain is known to interact with the HR domain of the inner membrane T2SS protein GspC. When the new N0 ring model is combined with the known N0·HR crystal structure, a dodecameric double-ring of twelve N0-HR heterodimers is obtained. In contrast, the previously observed compact N0-N1 GspD module is not compatible with the N0 ring. Interestingly, a N0-N1 T3SS homolog is compatible with forming a N0-N1 dodecameric ring, due to a different N0-vs-N1 orientation. This suggests that the dodecameric N0 ring is an important feature of T2SS secretins with periplasmic domains undergoing considerable motions during exoprotein translocation.

C57-CD40 ligand deficient mice: a potential model for enterotoxigenic Escherichia coli (H10407) colonization

Enterotoxigenic Escherichia coli (ETEC) are a major cause of diarrheal disease in humans, calves and pigs. In humans, these infections mainly occur in developing countries leading to a high diarrheal morbidity and infant mortality and to travellers' diarrhea. ETEC strains constitute a phenotypically and genetically diverse pathotype with as common characteristics the production of heat-labile (LT) and/or heat-stable enterotoxins (ST) as well as of one or more fimbrial colonization factors. Despite the global importance of these pathogens, a broadly ETEC protective vaccine is not yet available, partially due to the lack of a suitable animal model for human ETEC. Such model would allow to test more ETEC molecules as potential vaccine candidates. The C57-CD40 ligand deficient (C57-cd40l(-/-)) mouse has been successfully used to develop infection models of intestinal pathogens, but little is known about its humoral immune response. Therefore, the aims of this study were to characterize the humoral immune response of C57 and C57-cd40l(-/-) mice and to determine the persistence of ETEC H10407 and two of its variants after oral inoculation. The serum IgM, IgG and IgA and faecal IgG and IgA concentrations, of twelve mice per mouse strain (C57 and C57-cd40l(-/-)), were determined by ELISA. All serum immunoglobulins and the faecal IgG concentration were significantly lower in C57-cd40l(-/-) than in C57 mice. In contrast the faecal IgA concentration was significantly higher in the C57-cd40l(-/-) mice. This high intestinal IgA concentration might be a compensatory T cell-independent production of IgA production. Both mouse strains were orally inoculated with 5×10(8) ETEC H10407 (LT(+), ST-colonization factor antigen I (CFA/I)(+)) and ETEC in animal faeces was established by culture followed by st and lt loci identification by PCR until day 14 post infection. Most C57 mice eliminated the strain within 3 days whereas infection remained in C57-cd40l(-/-) mice until day 14. Subsequently both mouse strains were inoculated with ETEC H10407 variants and followed up until day 113. Likewise C57 mice eliminated both ETEC variants within 4 days. All C57-cd40l(-/-) mice had eliminated the LT(-) variant at day 31, whereas the ST-CFA/I(-) variant remained in mice stools until day 113. These observations suggest that C57-cd40l(-/-) mice are permissive for ETEC H10407 colonization.

Clinical implications of enteroadherent Escherichia coli

Pathogenic Escherichia coli that colonize the small intestine primarily cause gastrointestinal illness in infants and travelers. The main categories of pathogenic E. coli that colonize the epithelial lining of the small intestine are enterotoxigenic E. coli, enteropathogenic E. coli, and enteroaggregative E. coli. These organisms accomplish their pathogenic process by a complex, coordinated multistage strategy, including nonintimate adherence mediated by various adhesins. These so called "enteroadherent E. coli" categories subsequently produce toxins or effector proteins that are either secreted to the milieu or injected to the host cell. Finally, destruction of the intestinal microvilli results from the intimate adherence or the toxic effect exerted over the epithelia, resulting in water secretion and diarrhea. In this review, we summarize the current state of knowledge regarding these enteroadherent E. coli strains and the present clinical understanding of how these organisms colonize the human intestine and cause disease.

Molecular characterization of enterotoxigenic Escherichia coli isolates recovered from children with diarrhea during a 4-year period (2007 to 2010) in Bolivia

Enterotoxigenic Escherichia coli (ETEC) is an important cause of childhood diarrhea. This study aimed to characterize ETEC strains isolated from Bolivian children aged <5 years according to enterotoxin profile, colonization factors (CFs), suggested virulence genes, and severity of disease. A total of 299 ETEC isolates recovered from children with diarrhea and 55 ETEC isolates from children without diarrhea (controls) were isolated over a period of 4 years. Strains expressing heat-labile toxin (LT) or heat-stable toxin (ST) alone were about equally common and twice as common as ETEC producing both toxins (20%). ETEC strains expressing human ST (STh) were more common in children aged <2 years, while ETEC strains expressing LT plus STh (LT/STh) were more frequent in 2- to 5-year-old children. Severity of disease was not related to the toxin profile of the strains. CF-positive isolates were more frequently identified in diarrheal samples than in control samples (P = 0.02). The most common CFs were CFA/I and CS14. CFA/I ETEC strains were more frequent in children aged <2 years than CS1+CS3 isolates and CS14 isolates, which were more prevalent in 2- to 5-year-old children. The presence of suggested ETEC virulence genes (clyA, eatA, tia, tibC, leoA, and east-1) was not associated with disease. However, east-1 was associated with LT/STh strains (P < 0.001), eatA with STh strains (P < 0.001), and tia with LT/STh strains (P < 0.001). A minor seasonal peak of ETEC infections was identified in May during the cold-dry season and coincided with the peak of rotavirus infections; this pattern is unusual for ETEC and may be important for vaccination strategies in Bolivia.

Genotypic characterization of enterotoxigenic Escherichia coli strains causing traveler's diarrhea

This study aims to characterize the presence of virulence factors of enterotoxigenic Escherichia coli (ETEC) causing traveler's diarrhea. Among 52 ETEC isolates, the most common toxin type was STh, and the most frequent colonization factors (CFs) were CS21, CS6, and CS3. On the other hand, the nonclassical virulence factors EAST1 and EatA were frequently present.

Transcriptional modulation of enterotoxigenic Escherichia coli virulence genes in response to epithelial cell interactions

Enterotoxigenic Escherichia coli (ETEC) strains are a leading cause of morbidity and mortality due to diarrheal illness in developing countries. There is currently no effective vaccine against these important pathogens. Because genes modulated by pathogen-host interactions potentially encode putative vaccine targets, we investigated changes in gene expression and surface morphology of ETEC upon interaction with intestinal epithelial cells in vitro. Pan-genome microarrays, quantitative reverse transcriptase PCR (qRT-PCR), and transcriptional reporter fusions of selected promoters were used to study changes in ETEC transcriptomes. Flow cytometry, immunofluorescence microscopy, and scanning electron microscopy were used to investigate alterations in surface antigen expression and morphology following pathogen-host interactions. Following host cell contact, genes for motility, adhesion, toxin production, immunodominant peptides, and key regulatory molecules, including cyclic AMP (cAMP) receptor protein (CRP) and c-di-GMP, were substantially modulated. These changes were accompanied by visible changes in both ETEC architecture and the expression of surface antigens, including a novel highly conserved adhesin molecule, EaeH. The studies reported here suggest that pathogen-host interactions are finely orchestrated by ETEC and are characterized by coordinated responses involving the sequential deployment of multiple virulence molecules. Elucidation of the molecular details of these interactions could highlight novel strategies for development of vaccines for these important pathogens.

Enterotoxigenic Escherichia coli prevents host NF-κB activation by targeting IκBα polyubiquitination

The NF-κB pathway regulates innate immune responses to infection. NF-κB is activated after pathogen-associated molecular patterns are detected, leading to the induction of proinflammatory host responses. As a countermeasure, bacterial pathogens have evolved mechanisms to subvert NF-κB signaling. Enterotoxigenic Escherichia coli (ETEC) causes diarrheal disease and significant morbidity and mortality for humans in developing nations. The extent to which this important pathogen subverts innate immune responses by directly targeting the NF-κB pathway is an understudied topic. Here we report that ETEC secretes a heat-stable, proteinaceous factor that blocks NF-κB signaling normally induced by tumor necrosis factor (TNF), interleukin-1β, and flagellin. Pretreating intestinal epithelial cells with ETEC supernatant significantly blocked the degradation of the NF-κB inhibitor IκBα without affecting IκBα phosphorylation. Data from immunoprecipitation experiments suggest that the ETEC factor functions by preventing IκBα polyubiquitination. Inhibiting clathrin function blocked the activity of the secreted ETEC factor, suggesting that this yet-uncharacterized activity may utilize clathrin-dependent endocytosis to enter host cells. These data suggest that ETEC evades the host innate immune response by directly modulating NF-κB signaling.

Structure of the CFA/III major pilin subunit CofA from human enterotoxigenic Escherichia coli determined at 0.90 Å resolution by sulfur-SAD phasing

CofA, a major pilin subunit of colonization factor antigen III (CFA/III), forms pili that mediate small-intestinal colonization by enterotoxigenic Escherichia coli (ETEC). In this study, the crystal structure of an N-terminally truncated version of CofA was determined by single-wavelength anomalous diffraction (SAD) phasing using five sulfurs in the protein. Given the counterbalance between anomalous signal strength and the undesired X-ray absorption of the solvent, diffraction data were collected at 1.5 Å resolution using synchrotron radiation. These data were sufficient to elucidate the sulfur substructure at 1.38 Å resolution. The low solvent content (29%) of the crystal necessitated that density modification be performed with an additional 0.9 Å resolution data set to reduce the phase error caused by the small sulfur anomalous signal. The CofA structure showed the αβ-fold typical of type IVb pilins and showed high structural homology to that of TcpA for toxin-coregulated pili of Vibrio cholerae, including spatial distribution of key residues critical for pilin self-assembly. A pilus-filament model of CofA was built by computational docking and molecular-dynamics simulation using the previously reported filament model of TcpA as a structural template. This model revealed that the CofA filament surface was highly negatively charged and that a 23-residue-long loop between the α1 and α2 helices filled the gap between the pilin subunits. These characteristics could provide a unique binding epitope for the CFA/III pili of ETEC compared with other type IVb pili.

Cooperative role of antibodies against heat-labile toxin and the EtpA Adhesin in preventing toxin delivery and intestinal colonization by enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrheal disease in developing countries, where it is responsible for hundreds of thousands of deaths each year. Vaccine development for ETEC has been hindered by the heterogeneity of known molecular targets and the lack of broad-based sustained protection afforded by existing vaccine strategies. In an effort to explore the potential role of novel antigens in ETEC vaccines, we examined the ability of antibodies directed against the ETEC heat-labile toxin (LT) and the recently described EtpA adhesin to prevent intestinal colonization in vivo and toxin delivery to epithelial cells in vitro. We demonstrate that EtpA is required for the optimal delivery of LT and that antibodies against this adhesin play at least an additive role in preventing delivery of LT to target intestinal cells when combined with antibodies against either the A or B subunits of the toxin. Moreover, vaccination with a combination of LT and EtpA significantly impaired intestinal colonization. Together, these results suggest that the incorporation of recently identified molecules such as EtpA could be used to enhance current approaches to ETEC vaccine development.

Risks associated with high-dose Lactobacillus rhamnosus in an Escherichia coli model of piglet diarrhoea: intestinal microbiota and immune imbalances

Probiotic could be a promising alternative to antibiotics for the prevention of enteric infections; however, further information on the dose effects is required. In this study, weanling piglets were orally administered low- or high-dose Lactobacillus rhamnosus ACTT 7469 (10¹⁰ CFU/d or 10¹² CFU/d) for 1 week before F4 (K88)-positive Escherichia coli challenge. The compositions of faecal and gastrointestinal microbiota were recorded; gene expression in the intestines was assessed by real-time PCR; serum tumour necrosis factor-α (TNF-α) concentrations and intestinal Toll-like receptor 4 (TLR4) were detected by ELISA and immunohistochemistry, respectively. Unexpectedly, high-dose administration increased the incidence of diarrhoea before F4⁺ETEC challenge, despite the fact that both doses ameliorated F4⁺ETEC-induced diarrhoea with increased Lactobacillus and Bifidobacterium counts accompanied by reduced coliform shedding in faeces. Interestingly, L. rhamnosus administration reduced Lactobacillus and Bifidobacterium counts in the colonic contents, and the high-dose piglets also had lower Lactobacillius and Bacteroides counts in the ileal contents. An increase in the concentration of serum TNF-α induced by F4⁺ETEC was observed, but the increase was delayed by L. rhamnosus. In piglets exposed to F4⁺ETEC, jejunal TLR4 expression increased at the mRNA and protein levels, while jejunal interleukin (IL)-8 and ileal porcine β-defensins 2 (pBD2) mRNA expression increased; however, these increases were attenuated by administration of L. rhamnosus. Notably, expression of jejunal TLR2, ileal TLR9, Nod-like receptor NOD1 and TNF-α mRNA was upregulated in the low-dose piglets after F4⁺ETEC challenge, but not in the high-dose piglets. These findings indicate that pretreatment with a low dose of L. rhamnosus might be more effective than a high dose at ameliorating diarrhoea. There is a risk that high-dose L. rhamnosus pretreatment may negate the preventative effects, thus decreasing the prophylactic benefits against potential enteric pathogens. Our data suggest a safe threshold for preventative use of probiotics in clinical practice.

Isolation and epidemiological characterization of heat-labile enterotoxin-producing Escherichia fergusonii from healthy chickens

Escherichia fergusonii has been associated with a wide variety of intestinal and extraintestinal infections in both humans and animals. The aim of this study was to demonstrate the presence of heat-labile enterotoxin (LT)-producing E. fergusonii in healthy chickens and its plasmid-mediated LT toxin gene transfer to other Enterobacteriaceae. We tested faecal samples from 184 chicken flocks (consisting of 109 broilers and 75 layers) of 78 commercial chicken farms for the presence of the LT gene using a polymerase chain reaction-based screening and identified samples from 43 flocks (23.4%) as positive for the LT gene. We subsequently isolated and identified E. fergusonii harboring the LT gene from all LT-positive samples and observed 21 various biochemical types. The plasmids encoding LT in 16 (37.2%) of the 43 isolates were conjugally transferred to the recipient strain Escherichia coli J53. Southern hybridization showed that all plasmids from the transconjugants carried the eltAB gene (Ent plasmid) and belonged to the narrow-host-range IncF type. In addition, all the E. fergusonii strains identified were classified into 17 pulsed-field gel electrophoresis (PFGE) types, and it is likely that there was an association between the PFGE types and geographical location or breed of flocks. In conclusion, this is the first study to demonstrate that LT-producing E. fergusonii strains were present in the faeces of healthy chickens and that plasmid-mediated virulence genes can be transferred to E. coli and may have a great potential to cause human disease.

Heat-labile enterotoxin-induced activation of NF-κB and MAPK pathways in intestinal epithelial cells impacts enterotoxigenic Escherichia coli (ETEC) adherence

Enterotoxigenic Escherichia coli (ETEC) causes human morbidity and mortality in developing nations and is an emerging threat to food safety in developed nations. The ETEC heat-labile enterotoxin (LT) not only causes diarrheal disease by deregulating host adenylate cyclase, but also enhances ETEC adherence to intestinal epithelial cells. The mechanism governing this LT pro-adherence phenotype is unclear. Here we investigated intestinal epithelial cell signal transduction pathways activated by ETEC and quantified the relative importance of these host pathways to LT-induced ETEC adherence. We show that ETEC activates both NF-κB and mitogen-activated protein kinase signalling pathways through mechanisms that are primarily dependent upon LT. LT-induced NF-κB activation depends upon the cAMP-dependent activation of the Ras-like GTPase Rap1 but is independent of protein kinase A (PKA). By using inhibitors of these pathways, we demonstrate that inhibiting the p38 mitogen-activated protein kinase prevents LT from increasing ETEC adherence. By contrast, the LT pro-adherence phenotype appears unrelated to both LT-induced Rap1 activity and to subsequent NF-κB activation. We speculate that LT may alter host signal transduction to induce the presentation of ligands for ETEC adhesins in such a way that promotes ETEC adherence. Our findings provide insight into previously unexplored functions of LT and their relative importance to ETEC virulence.

Inhibiting host-pathogen interactions using membrane-based nanostructures

Virulent strains of bacteria and viruses recognize host cells by their plasma membrane receptors and often exploit the native translocation machinery to invade the cell. A promising therapeutic concept for early interruption of pathogen infection is to subvert this pathogenic trickery using exogenously introduced decoys that present high-affinity mimics of cellular receptors. This review highlights emerging applications of molecularly engineered lipid-bilayer-based nanostructures, namely (i) functionalized liposomes, (ii) supported colloidal bilayers or protocells and (iii) reconstituted lipoproteins, which display functional cellular receptors in optimized conformational and aggregative states. These decoys outcompete host cell receptors by preferentially binding to and neutralizing virulence factors of both bacteria and viruses, thereby promising a new approach to antipathogenic therapy.

Outbreak of Shiga toxin-producing Escherichia coli (STEC) O104:H4 infection in Germany causes a paradigm shift with regard to human pathogenicity of STEC strains

An outbreak that comprised 3,842 cases of human infections with enteroaggregative hemorrhagic Escherichia coli (EAHEC) O104:H4 occurred in Germany in May 2011. The high proportion of adults affected in this outbreak and the unusually high number of patients that developed hemolytic uremic syndrome makes this outbreak the most dramatic since enterohemorrhagic E. coli (EHEC) strains were first identified as agents of human disease. The characteristics of the outbreak strain, the way it spread among humans, and the clinical signs resulting from EAHEC infections have changed the way Shiga toxin-producing E. coli strains are regarded as human pathogens in general. EAHEC O104:H4 is an emerging E. coli pathotype that is endemic in Central Africa and has spread to Europe and Asia. EAHEC strains have evolved from enteroaggregative E. coli by uptake of a Shiga toxin 2a (Stx2a)-encoding bacteriophage. Except for Stx2a, no other EHEC-specific virulence markers including the locus of enterocyte effacement are present in EAHEC strains. EAHEC O104:H4 colonizes humans through aggregative adherence fimbrial pili encoded by the enteroaggregative E. coli plasmid. The aggregative adherence fimbrial colonization mechanism substitutes for the locus of enterocyte effacement functions for bacterial adherence and delivery of Stx2a into the human intestine, resulting clinically in hemolytic uremic syndrome. Humans are the only known natural reservoir known for EAHEC. In contrast, Shiga toxin-producing E. coli and EHEC are associated with animals as natural hosts. Contaminated sprouted fenugreek seeds were suspected as the primary vehicle of transmission of the EAHEC O104:H4 outbreak strain in Germany. During the outbreak, secondary transmission (human to human and human to food) was important. Epidemiological investigations revealed fenugreek seeds as the source of entry of EAHEC O104:H4 into the food chain; however, microbiological analysis of seeds for this pathogen produced negative results. The survival of EAHEC in seeds and the frequency of human carriers of EAHEC should be investigated for a better understanding of EAHEC transmission routes.

Analysis of global transcriptional profiles of enterotoxigenic Escherichia coli isolate E24377A

Enterotoxigenic Escherichia coli (ETEC) is an important pathogenic variant (pathovar) of E. coli in developing countries from a human health perspective, causing significant morbidity and mortality. Previous studies have examined specific regulatory networks in ETEC, although little is known about the global effects of inter- and intrakingdom signaling on the expression of virulence and colonization factors in ETEC. In this study, an E. coli/Shigella pan-genome microarray, combined with quantitative reverse transcriptase PCR (qRT-PCR) and RNA sequencing (RNA-seq), was used to quantify the expression of ETEC virulence and colonization factors. Biologically relevant chemical signals were combined with ETEC isolate E24377A during growth in either Luria broth (LB) or Dulbecco's modified Eagle medium (DMEM), and transcription was examined during different phases of the growth cycle; chemical signals examined included glucose, bile salts, and preconditioned media from E. coli/Shigella isolates. The results demonstrate that the presence of bile salts, which are found in the intestine and thought to be bactericidal, upregulates the expression of many ETEC virulence factors, including heat-stable (estA) and heat-labile (eltA) enterotoxin genes. In contrast, the ETEC colonization factors CS1 and CS3 were downregulated in the presence of bile, consistent with findings in studies of other enteric pathogens. RNA-seq analysis demonstrated that one of the most differentially expressed genes in the presence of bile is a unique plasmid-encoded AraC-like transcriptional regulator (peaR); other previously unknown genetic elements were found as well. These results provide transcriptional targets and putative mechanisms that should help improve understanding of the global regulatory networks and virulence expression in this important human pathogen.

Adaptive evolution of class 5 fimbrial genes in enterotoxigenic Escherichia coli and its functional consequences

Class 5 fimbriae of enterotoxigenic Escherichia coli (ETEC) comprise eight serologically discrete colonization factors that mediate small intestinal adhesion. Their differentiation has been attributed to the pressure imposed by host adaptive immunity. We sequenced the major pilin and minor adhesin subunit genes of a geographically diverse population of ETEC elaborating CFA/I (n = 31), CS17 (n = 20), and CS2 (n = 18) and elucidated the functional effect of microevolutionary processes. Between the fimbrial types, the pairwise nucleotide diversity for the pilin or adhesin genes ranged from 35-43%. Within each fimbrial type, there were 17 non-synonymous and 1 synonymous point mutations among all pilin or adhesin gene copies, implying that each fimbrial type was acquired by ETEC strains very recently, consistent with a recent origin of this E. coli pathotype. The 17 non-synonymous allelic differences occurred in the CFA/I pilin gene cfaB (two changes) and adhesin gene cfaE (three changes), and CS17 adhesin gene csbD (12 changes). All but one amino acid change in the adhesins clustered around the predicted ligand-binding pocket. Functionally, these changes conferred an increase in cell adhesion in a flow chamber assay. In contrast, the two mutations in the non-adhesive CfaB subunit localized to the intersubunit interface and significantly reduced fimbrial adhesion in this assay. In conclusion, naturally occurring mutations in the ETEC adhesive and non-adhesive subunits altered function, were acquired under positive selection, and are predicted to impact bacteria-host interactions.

Directed evaluation of enterotoxigenic Escherichia coli autotransporter proteins as putative vaccine candidates

Background

Enterotoxigenic Escherichia coli (ETEC) is a major diarrheal pathogen in developing countries, where it accounts for millions of infections and hundreds of thousands of deaths annually. While vaccine development to prevent diarrheal illness due to ETEC is feasible, extensive effort is needed to identify conserved antigenic targets. Pathogenic Escherichia coli, including ETEC, use the autotransporter (AT) secretion mechanism to export virulence factors. AT proteins are comprised of a highly conserved carboxy terminal outer membrane beta barrel and a surface-exposed amino terminal passenger domain. Recent immunoproteomic studies suggesting that multiple autotransporter passenger domains are recognized during ETEC infection prompted the present studies.

Methodology

Available ETEC genomes were examined to identify AT coding sequences present in pathogenic isolates, but not in the commensal E. coli HS strain. Passenger domains of the corresponding autotransporters were cloned and expressed as recombinant antigens, and the immune response to these proteins was then examined using convalescent sera from patients and experimentally infected mice.

Principal Findings

Potential AT genes shared by ETEC strains, but absent in the E. coli commensal HS strain were identified. Recombinant passenger domains derived from autotransporters, including Ag43 and an AT designated pAT, were recognized by antibodies from mice following intestinal challenge with H10407, and both Ag43 and pAT were identified on the surface of ETEC by flow cytometry. Likewise, convalescent sera from patients with ETEC diarrhea recognized Ag43 and pAT, suggesting that these proteins are expressed during both experimental and naturally occurring ETEC infections and that they are immunogenic. Vaccination of mice with recombinant passenger domains from either pAT or Ag43 afforded protection against intestinal colonization with ETEC.

Conclusions

Passenger domains of conserved autotransporter proteins could contribute to protective immune responses that develop following infection with ETEC, and these antigens consequently represent potential targets to explore in vaccine development.

Diarrheal diseases are responsible for more than 1.5 million deaths annually in developing countries. Enterotoxigenic E. coli (ETEC) are among the most common bacterial causes of diarrhea, accounting for an estimated 300,000–500,000 deaths each year, mostly in young children. There unfortunately is not yet a vaccine that can offer sustained, broad-based protection against ETEC. While most vaccine development effort has focused on plasmid-encoded finger-like ETEC adhesin structures known as colonization factors, additional effort is needed to identify conserved target antigens. Epidemiologic studies suggest that immune responses to uncharacterized, chromosomally encoded antigens could contribute to protection resulting from repeated infections. Earlier studies of immune responses to ETEC infection had identified a class of surface-expressed molecules known as autotransporters (AT). Therefore, available ETEC genome sequences were examined to identify conserved ETEC autotransporters not shared by the commensal E. coli HS strain, followed by studies of the immune response to these antigens, and tests of their utility as vaccine components. Two chromosomally encoded ATs, identified in ETEC, but not in HS, were found to be immunogenic and protective in an animal model, suggesting that conserved AT molecules contribute to protective immune responses that follow natural ETEC infection and offering new potential targets for vaccines.

Serum antibodies protect against intraperitoneal challenge with enterotoxigenic Escherichia coli

To assess whether anticolonization factor antigen I (CFA/I) fimbriae antibodies (Abs) from enterotoxigenic Escherichia coli (ETEC) can protect against various routes of challenge, BALB/c mice were immunized with a live attenuated Salmonella vaccine vector expressing CFA/I fimbriae. Vaccinated mice elicited elevated systemic IgG and mucosal IgA Abs, unlike mice immunized with the empty Salmonella vector. Mice were challenged with wild-type ETEC by the oral, intranasal (i.n.), and intraperitoneal (i.p.) routes. Naïve mice did not succumb to oral challenge, but did to i.n. challenge, as did immunized mice; however, vaccinated mice were protected against i.p. ETEC challenge. Two intramuscular (i.m.) immunizations with CFA/I fimbriae without adjuvant conferred 100% protection against i.p. ETEC challenge, while a single 30 μg dose conferred 88% protection. Bactericidal assays showed that ETEC is highly sensitive to anti-CFA/I sera. These results suggest that parenteral immunization with purified CFA/I fimbriae can induce protective Abs and may represent an alternative method to elicit protective Abs for passive immunity to ETEC.

Adhesin degradation accelerates delivery of heat-labile toxin by enterotoxigenic Escherichia coli

Many enteric pathogens, including enterotoxigenic Escherichia coli (ETEC), produce one or more serine proteases that are secreted via the autotransporter (or type V) bacterial secretion pathway. These molecules have collectively been referred to as SPATE proteins (serine protease autotransporter of the Enterobacteriaceae). EatA, an autotransporter previously identified in ETEC, possesses a functional serine protease motif within its secreted amino-terminal passenger domain. Although this protein is expressed by many ETEC strains and is highly immunogenic, its precise function is unknown. Here, we demonstrate that EatA degrades a recently characterized adhesin, EtpA, resulting in modulation of bacterial adhesion and accelerated delivery of the heat-labile toxin, a principal ETEC virulence determinant. Antibodies raised against the passenger domain of EatA impair ETEC delivery of labile toxin to epithelial cells suggesting that EatA may be an effective target for vaccine development.

Loss of PDZ-adaptor protein NHERF2 affects membrane localization and cGMP- and [Ca2+]- but not cAMP-dependent regulation of Na+/H+ exchanger 3 in murine intestine

Trafficking and regulation of the epithelial brush border membrane (BBM) Na+/H+ exchanger 3 (NHE3) in the intestine involves interaction with four different members of the NHERF family in a signal-dependent and possibly segment-specific fashion. The aim of this research was to study the role of NHERF2 (E3KARP) in intestinal NHE3 BBM localization and second messenger-mediated and receptor-mediated inhibition of NHE3. Immunolocalization of NHE3 in WT mice revealed predominant microvillar localization in jejunum and colon, a mixed distribution in the proximal ileum but localization near the terminal web in the distal ileum. The terminal web localization of NHE3 in the distal ileum correlated with reduced acid-activated NHE3 activity (fluorometrically assessed). NHERF2 ablation resulted in a shift of NHE3 to the microvilli and higher basal fluid absorption rates in the ileum, but no change in overall NHE3 protein or mRNA expression. Forskolin-induced NHE3 inhibition was preserved in the absence of NHERF2, whereas Ca2+ ionophore- or carbachol-mediated inhibition was abolished. Likewise, Escherichia coli heat stable enterotoxin peptide (STp) lost its inhibitory effect on intestinal NHE3. It is concluded that in native murine intestine, the NHE3 adaptor protein NHERF2 plays important roles in tethering NHE3 to a position near the terminal web and in second messenger inhibition of NHE3 in a signal- and segment-specific fashion, and is therefore an important regulator of intestinal fluid transport.

Food poisoning and diarrhea: small intestine effects

Transmission of foodborne pathogens remains a growing concern despite increasing public awareness and heightened federal measures to control infection. Over 76 million cases of acute diarrhea secondary to ingestion of contaminated food occur annually in the United States. Fortunately, most are self-limited and resolve without therapy, but up to 6000 deaths occur on an annual basis. Mechanisms of infection include consumption of a preformed toxin, formation of toxin following ingestion, and direct invasion of intestinal epithelial cells by the infecting organism. Diagnosis is most often confirmed through an accurate history, as cultures are often of low yield.

Analysis of the resistome of a multidrug-resistant NDM-1-producing Escherichia coli strain by high-throughput genome sequencing

The resistome of the multidrug-resistant Escherichia coli strain 271 carrying the plasmid-mediated bla(NDM-1) carbapenemase gene was analyzed by high-throughput genome sequencing. The p271A plasmid carrying the bla(NDM-1) gene was 35.9 kb in size and possessed an IncN-type backbone that harbored a novel replicase gene. Acquisition of the bla(NDM-1) gene on plasmid p271A had been likely the result of a cointegration event involving the transposase of Tn5403. The expression of bla(NDM-1) was associated with the insertion sequence ISAba125 likely originating from Acinetobacter baumannii. E. coli 271 accumulated multiple resistance determinants, including five β-lactamase genes (comprising the extended-spectrum β-lactamase CTX-M-15), two 16S RNA methylase ArmA- and RmtB-encoding genes, and the qepA gene encoding an efflux pump involved in resistance to fluoroquinolones. These resistance genes were located on three additional plasmids, of 160 kb (IncA/C), 130 kb (IncF), and 110 kb (IncI1). In addition, several chromosomally encoded resistance determinants were identified, such as topoisomerase mutations, porin modifications and truncations, and the intrinsic ampC gene of E. coli that was weakly expressed. The multidrug resistance pattern observed for E. coli 271 was therefore the result of combined chromosome- and plasmid-encoded mechanisms.

Enterotoxigenic Escherichia coli CS6 gene products and their roles in CS6 structural protein assembly and cellular adherence

Enterotoxigenic Escherichia coli (ETEC) produces a variety of colonization factors necessary for attachment to the host cell, among which CS6 is one of the most prevalent in ETEC isolates from developing countries. The CS6 operon is composed of 4 genes, cssA, cssB, cssC, and cssD. The molecular mechanism of CS6 assembly and cell surface presentation, and the contribution of each protein to the attachment of the bacterium to intestinal cells remain unclear. In the present study, a series of css gene-deletion mutants of the CS6 operon were constructed in the ETEC genetic background, and their effect on adhesion to host cells and CS6 assembly was studied. Each subunit deletion resulted in a reduction in the adhesion to intestinal cells to the same level of laboratory E. coli strains, and this effect was restored by complementary plasmids, suggesting that the 4 proteins are necessary for CS6 expression. Bacterial cell fractionation and western blotting of the mutant strains suggested that the formation of a CssA-CssB-CssC complex is necessary for recognition by CssD and transport of CssA-CssB to the outer membrane as a colonization factor.

Context-dependent activation kinetics elicited by soluble versus outer membrane vesicle-associated heat-labile enterotoxin

Enterotoxigenic Escherichia coli (ETEC) is the leading cause of traveler's diarrhea and children's diarrhea worldwide. Among its virulence factors, ETEC produces heat-labile enterotoxin (LT). Most secreted LT is associated with outer membrane vesicles that are rich in lipopolysaccharide. The majority of prior studies have focused on soluble LT purified from ETEC periplasm. We investigated the hypothesis that the extracellular vesicle context of toxin presentation might be important in eliciting immune responses. We compared the polarized epithelial cell responses to apically applied soluble LT and LT-containing vesicles (LT(+) vesicles) as well as controls using a catalytically inactive mutant of LT and vesicles lacking LT. Although vesicle treatments with no or catalytically inactive LT induced a modest amount of interleukin-6 (IL-6), samples containing catalytically active LT elicited higher levels. A combination of soluble LT and LT-deficient vesicles induced significantly higher IL-6 levels than either LT or LT(+) vesicles alone. The responses to LT(+) vesicles were found to be independent of the canonical LT pathway, because the inhibition of cyclic AMP response element (CRE)-binding protein (CREB) phosphorylation did not lead to a decrease in cytokine gene expression levels. Furthermore, soluble LT caused earlier phosphorylation of CREB and activation of CRE compared with LT(+) vesicles. Soluble LT also led to the activation of activator protein 1, whereas LT(+) vesicle IL-6 responses appeared to be mediated by NF-κB. In summary, the results demonstrate that soluble LT and vesicle-bound LT elicit ultimately similar cytokine responses through distinct different activation pathways.

Induction of increased permeability of polarized enterocyte monolayers by enterotoxigenic Escherichia coli heat-labile enterotoxin

Enterotoxigenic Escherichia coli (ETEC) is a common cause of acute diarrhea in resource-poor settings. We report that some ETEC strains elicit a reduction in trans-epithelial electrical resistance (TER) in polarized T84 epithelial cell monolayers. The effect was irreversible up to 48 hours after a three-hour infection and was observed with heat-labile enterotoxin (LT)-producing strains, but not with heat-stable enterotoxin (ST)-producing strains. Using purified LT, a mutant with reduced ADP-ribosylating activity, and the LT-B subunit alone, we demonstrate that TER reduction requires a functional enterotoxin. Treatment of monolayers with LT or LT-producing strains of ETEC increases paracellular permeability to fluorescein isothiocyanate-dextran. Our data suggest that LT-producing ETEC strains may induce intestinal barrier dysfunction.

A comparative genomic analysis of diverse clonal types of enterotoxigenic Escherichia coli reveals pathovar-specific conservation

Enterotoxigenic Escherichia coli (ETEC) is a major cause of diarrheal illness in children less than 5 years of age in low- and middle-income nations, whereas it is an emerging enteric pathogen in industrialized nations. Despite being an important cause of diarrhea, little is known about the genomic composition of ETEC. To address this, we sequenced the genomes of five ETEC isolates obtained from children in Guinea-Bissau with diarrhea. These five isolates represent distinct and globally dominant ETEC clonal groups. Comparative genomic analyses utilizing a gene-independent whole-genome alignment method demonstrated that sequenced ETEC strains share approximately 2.7 million bases of genomic sequence. Phylogenetic analysis of this "core genome" confirmed the diverse history of the ETEC pathovar and provides a finer resolution of the E. coli relationships than multilocus sequence typing. No identified genomic regions were conserved exclusively in all ETEC genomes; however, we identified more genomic content conserved among ETEC genomes than among non-ETEC E. coli genomes, suggesting that ETEC isolates share a genomic core. Comparisons of known virulence and of surface-exposed and colonization factor genes across all sequenced ETEC genomes not only identified variability but also indicated that some antigens are restricted to the ETEC pathovar. Overall, the generation of these five genome sequences, in addition to the two previously generated ETEC genomes, highlights the genomic diversity of ETEC. These studies increase our understanding of ETEC evolution, as well as provide insight into virulence factors and conserved proteins, which may be targets for vaccine development.