Simultaneous exposure to Escherichia coli heat-labile and heat-stable enterotoxins increases fluid secretion and alters cyclic nucleotide and cytokine production by intestinal epithelial cells

Impacts of F18+Escherichia coli on Intestinal Health of Nursery Pigs and Dietary Interventions

This review focused on the impact of F18+E. coli on pig production and explored nutritional interventions to mitigate its deleterious effects. F18+E. coli is a primary cause of PWD in nursery pigs, resulting in substantial economic losses through diminished feed efficiency, morbidity, and mortality. In summary, the F18+E. coli induces intestinal inflammation with elevated IL6 (60%), IL8 (43%), and TNF-α (28%), disrupting the microbiota and resulting in 14% villus height reduction. Besides the mortality, the compromised intestinal health results in a 20% G:F decrease and a 10% ADFI reduction, ultimately culminating in a 28% ADG decrease. Among nutritional interventions to counter F18+E. coli impacts, zinc glycinate lowered TNF-α (26%) and protein carbonyl (45%) in jejunal mucosa, resulting in a 39% ADG increase. Lactic acid bacteria reduced TNF-α (36%), increasing 51% ADG, whereas Bacillus spp. reduced IL6 (27%), increasing BW (12%). Lactobacillus postbiotic increased BW (14%) and the diversity of beneficial bacteria. Phytobiotics reduced TNF-α (23%) and IL6 (21%), enhancing feed efficiency (37%). Additional interventions, including low crude protein formulation, antibacterial minerals, prebiotics, and organic acids, can be effectively used to combat F18+E. coli infection. These findings collectively underscore a range of effective strategies for managing the challenges posed by F18+E. coli in pig production.

Heat-Stable Enterotoxin Secretions Assessed via ICP-MS Reveal Iron-Mediated Regulation of Virulence in CFA/I- and CS6-Expressing ETEC Isolates

Enterotoxigenic Escherichia coli (ETEC) are a significant cause of childhood diarrhea in low-resource settings. ETEC are defined by the production of heat-stable enterotoxin (ST) and/or heat-labile enterotoxin (LT), which alter intracellular cyclic nucleotide signaling and cause the secretion of water and electrolytes into the intestinal lumen. ETEC take cues from chemicals (e.g., glycans, bile salts, and solutes) that may be liberated following enterotoxin activity to recognize entrance into the host. ETEC then alter the expression of surface adhesins called colonization factors (CFs) to attach to the intestinal epithelium, proliferate, and cause disease. Here, we used an in vivo model of oral ST intoxication to determine its impact on luminal ion concentrations via ICP-MS. We also used functional assays, including Western blots, qPCR, and toxin activity assays, to assess the impact of luminal ion flux on CF and toxin expression. Finally, we assessed ETEC strains with CFs CFA/I or CS6 in a streptomycin mouse model of ETEC colonization. ST causes rapid and significant increases in luminal chloride but significant decreases in luminal magnesium and iron. We confirmed that increased sodium chloride suppresses CFA/I production in ETEC H10407 but does not affect CS6 production in ETEC 214-4. CFA/I production in ETEC H10407 is increased when magnesium becomes limiting, although it does not affect CS6 production in ETEC 214-4. Iron restriction via deferoxamine induces CFA/I expression in ETEC H10407 but not CS6 expression in ETEC 214-4. We demonstrate that ST production is suppressed via iron restriction in H10407, 214-4, and over 50 other ETEC clinical isolates. Lastly, we demonstrate that the iron restriction of mice using oral deferoxamine pre-treatment extends the duration of ETEC H10407 (CFA/I⁺) fecal shedding while accelerating ETEC 214-4 (CS6⁺) fecal shedding. Combined, these data suggest that enterotoxins modulate luminal ion flux to influence ETEC virulence including toxin and CF production.

Dual-Use Vaccine for Diarrhoeal Diseases: Cross-Protective Immunogenicity of a Cold-Chain-Free, Live-Attenuated, Oral Cholera Vaccine against Enterotoxigenic Escherichia coli (ETEC) Challenge in BALB/c Mice

In low- and middle-income countries, diarrhoeal diseases are the second most common cause of mortality in children, mainly caused by enterotoxin-producing bacteria, such as Shigella, Vibrio, Salmonella, and Escherichia coli. Cholera and traveller's diarrhoea are caused by Vibrio cholerae (O1 and O139 serogroups) and enterotoxigenic Escherichia coli (ETEC), respectively. The cholera toxin (CT) produced by V. cholerae and the heat-labile enterotoxin (LT) of ETEC are closely related by structure, function, and the immunological response to them. There is no exclusive vaccine for ETEC; however, cholera vaccines based on the CT-B component elicit a short-term cross-protection against ETEC infection. In this context, the cross-protective efficacy of MyChol^TM, a prototype cold-chain-free, live-attenuated, oral cholera vaccine against V. cholerae O139 was evaluated in BALB/c mice. The 100% lethal dose (LD₁₀₀) of 10⁹ CFU/mL of the ETEC H10407 strain was used for the challenge studies. The mice immunised with MyChol™ survived the challenge by producing anti-CT antibodies, which cross-neutralised the LT toxin with no body weight loss and no sign of diarrhoea. Compared to unimmunised mice, the immunised mice elicited the neutralising antitoxin that markedly decreased ETEC colonisation and fluid accumulation caused by ETEC H10407 in the intestines. The immunised mice recorded higher antibody titres, including anti-CT IgG, anti-LT IgG, anti-CT-B IgG, and anti-LTB IgG. Only a two-fold rise in anti-CT/CT-B/LT/LT-B IgA was recorded in serum samples from immunised mice. No bactericidal antibodies against ETEC H10407 were detected. This investigation demonstrates the safety, immunogenicity, and cross-protective efficacy of MyChol^TM against the ETEC H10407 challenge in BALB/c mice.

Feasibility of avian antibodies as prophylaxis against enterotoxigenic escherichia coli colonization

Background

This research aims to evaluate the feasibility of using avian immunoglobulins (IgY) raised against adhesion factors of enterotoxigenic Escherichia coli (ETEC) as prophylaxis of diarrheal illness caused by these pathogens. ETEC requires adhesion to human intestinal epithelial cells as a primary step in establishing enteric infection. Therefore, inhibition of adhesion may prevent such infections and reduce clinical burdens of diarrheal illness.

Methods

IgY samples were prepared from eggs of hens immunized with an adhesin-tip multiepitope fusion antigen (MEFA), developed against nine adhesin tip epitopes derived from clinically relevant ETEC strains. The resulting IgY was evaluated for its ability to inhibit adhesion of ETEC to cell-surface targets. Potential impacts of anti-MEFA IgY on growth of both pathogenic and commensal E. coli isolates were also evaluated.

Results

Enzyme linked immunosorbent assay (ELISA) titers were achieved for IgY targeting each of the nine individual epitopes included in the adhesin-tip MEFA. Furthermore, anti-MEFA titers exceeding 1:2¹⁹ were sustained for at least 23 weeks. All ETEC strains used in design of the adhesin-tip MEFA, and five of five clinical ETEC strains were significantly (P < 0.05) inhibited from adhesion to mammalian cells in culture.

Conclusions

These findings demonstrate that IgY targeting ETEC adhesin-tip MEFA have the potential to disrupt in vitro adherence of ETEC. A formulation containing adhesin-tip MEFA IgY can be considered a potential candidate for in vivo evaluation as prophylaxis of diarrheal diseases. Animal studies of this formulation are planned.

Impaired intestinal stem cell activity in ETEC infection: enterotoxins, cyclic nucleotides, and Wnt signaling

Enterotoxigenic Escherichia coli (ETEC) in humans and animals colonizes the intestine and thereafter secrets heat-stable enterotoxin (ST) with or without heat-labile enterotoxin (LT), which triggers massive fluid and electrolyte secretion into the gut lumen. The crosstalk between the cyclic nucleotide-dependent protein kinase/cystic fibrosis transmembrane conductance regulator (cAMP or cGMP/CFTR) pathway involved in ETEC-induced diarrhea channels, and the canonical Wnt/β-catenin signaling pathway leads to changes in intestinal stem cell (ISC) fates, which are strongly associated with developmental disorders caused by diarrhea. We review how alterations in enterotoxin-activated ion channel pathways and the canonical Wnt/β-catenin signaling pathway can explain inhibited intestinal epithelial activity, characterize alterations in the crosstalk of cyclic nucleotides, and predict harmful effects on ISCs in targeted therapy. Besides, we discuss current deficits in the understanding of enterotoxin-intestinal epithelial cell activity relationships that should be considered when interpreting sequelae of diarrhea.

Enterotoxigenic Escherichia coli enterotoxins regulate epithelial to immune relay of IL-33 and IL-1Ra cytokines

Enterotoxigenic Escherichia coli (ETEC) remain a major cause of diarrheal mortality and morbidity in children in low-resource settings. Few studies have explored the consequences of simultaneous intoxication with heat-stable (ST) and heat-labile (LT) enterotoxins despite the increased prevalence of wild ETEC isolates expressing both toxins. We therefore used a combination of tissue culture and murine models to explore the impact of simultaneous ST+LT intoxication of epithelial and myeloid cell responses. We report that LT induces sustained IL-33 and IL-1Ra responses in T84 intestinal epithelial cells via cAMP-production and protein kinase A activation. We demonstrate that combined ST+LT intoxication hastens epithelial transcriptional responses induced more slowly by LT alone. ST- and LT-mediated luminal fluid accumulation in vivo correlates with significant increases in IL-33 and IL-1Ra in small intestinal mucosal scrapings. Additionally, IL-33 receptor (IL-33R)-deficient mice are less susceptible to ST-mediated secretion. In the immune compartment, IL-33 is sensed by myeloid cells, and LT suppresses IL-33-induced TNFα secretion from macrophages but amplifies IL-33-mediated induction of IL-6 from bone marrow-derived dendritic cells. In conclusion, our studies suggest that enterotoxin-induced IL-33 and IL-1Ra modulate intestinal inflammation and IL-1 receptor signaling in the intestinal mucosa in response to ETEC enterotoxins.

Vaccines for Protecting Infants from Bacterial Causes of Diarrheal Disease

The global diarrheal disease burden for Shigella, enterotoxigenic Escherichia coli (ETEC), and Campylobacter is estimated to be 88M, 75M, and 75M cases annually, respectively. A vaccine against this target trio of enteric pathogens could address about one-third of diarrhea cases in children. All three of these pathogens contribute to growth stunting and have demonstrated increasing resistance to antimicrobial agents. Several combinations of antigens are now recognized that could be effective for inducing protective immunity against each of the three target pathogens in a single vaccine for oral administration or parenteral injection. The vaccine combinations proposed here would result in a final product consistent with the World Health Organization's (WHO) preferred product characteristics for ETEC and Shigella vaccines, and improve the vaccine prospects for support from Gavi, the Vaccine Alliance, and widespread uptake by low- and middle-income countries' (LMIC) public health stakeholders. Broadly protective antigens will enable multi-pathogen vaccines to be efficiently developed and cost-effective. This review describes how emerging discoveries for each pathogen component of the target trio could be used to make vaccines, which could help reduce a major cause of poor health, reduced cognitive development, lost economic productivity, and poverty in many parts of the world.

Elevated Extracellular cGMP Produced after Exposure to Enterotoxigenic Escherichia coli Heat-Stable Toxin Induces Epithelial IL-33 Release and Alters Intestinal Immunity

Enterotoxigenic Escherichia coli (ETEC) is a major diarrheal pathogen in children in low- to middle-income countries. Previous studies identified heat-stable enterotoxin (ST)-producing ETEC as a prevalent diarrheal pathogen in children younger than 5 years.

Enterotoxigenic Escherichia coli (ETEC) is a major diarrheal pathogen in children in low- to middle-income countries. Previous studies identified heat-stable enterotoxin (ST)-producing ETEC as a prevalent diarrheal pathogen in children younger than 5 years. While many studies have evaluated the interaction of ETEC heat-labile enterotoxin (LT) with host epithelium and immunity, few investigations have attempted similar studies with ST. To further understand ST pathogenesis, we examined the impact of ST on cGMP localization, epithelial cell cytokine production, and antibody development following immunization. In addition to robust intracellular cGMP in T84 cells in the presence of phosphodiesterase inhibitors (PDEis) that prevent the breakdown of cyclic nucleotides, we found that prolonged ST intoxication induced extracellular cGMP accumulation in the presence or absence of PDEis. Further, ST intoxication induced luminal cGMP in vivo in mice, suggesting that secreted cGMP may have other cellular functions. Using transcriptome sequencing (RNA-seq) and quantitative PCR (qPCR), we demonstrated that ST intoxication, or treatment with the clinically used ST mimic linaclotide, altered inflammatory cytokine gene expression, including the interleukin 1 (IL-1) family member IL-33, which could also be induced by cell-permeative 8-Br-cGMP. Finally, when present during immunization, ST suppressed induction of antibodies to specific antigens. In conclusion, our studies indicate that ST modulates epithelial cell physiology and the interplay between the epithelial and immune compartments.

Molecular mechanism of Escherichia coli H10407 induced diarrhoea and its control through immunomodulatory action of bioactives from Simarouba amara (Aubl.)

Enterotoxigenic Escherichia coli (ETEC) infection is a major cause of death in children under the age of five in developing countries. ETEC (O78:H11:CFA/I:LT⁺:ST⁺) mechanism has been studied in detail with either heat labile (LT) or heat stable (ST) toxins using in vitro and in vivo models. However, there is no adequate information on ETEC pathogenesis producing both the toxins (LT, ST) in BALB/c mice model. In this study, female mice have been employed to understand ETEC H10407 infection induced changes in physiology, biochemical and immunological patterns up to seven days post-infection and the antidiarrhoeal effect of Simarouba amara (Aubl.) bark aqueous extract (SAAE) has also been looked into. The results indicate that BALB/c is sensitive to ETEC infection resulting in altered jejunum and ileum histomorphology. Withal, ETEC influenced cAMP, PGE2, and NO production resulting in fluid accumulation with varied Na⁺, K⁺, Cl^-, and Ca²⁺ levels. Meanwhile, ETEC subverted expression of IL-1β, intestine alkaline phosphatase (IAP), and myeloperoxidase (MPO) in jejunum and ileum. Our data also indicate the severity of pathogenesis reduction which might be due to attainment of equilibrium after reaching optimum rate of infection. Nevertheless, degree of pathogenesis was highly significant (p < 0.01) in all the studied parameters. Besides that, SAAE was successful in reducing the infectious diarrhoea by inhibiting ETEC H10407 in intestine (jejunum and ileum), and shedding in feces. SAAE decreased cAMP, PGE2, and fluid accumulation effectively and boosted the functional activity of immune system in jejunum and ileum IAP, MPO, IL-1β, and nitric oxide.

Refinement of the CS6-expressing enterotoxigenic Escherichia coli strain B7A human challenge model: A randomized trial

Background

Human challenge models for enterotoxigenic Escherichia coli (ETEC) facilitate vaccine down-selection. The B7A (O148:H28 CS6⁺LT⁺ST⁺) strain is important for vaccine development. We sought to refine the B7A model by identifying a dose and fasting regimen consistently inducing moderate-severe diarrhea.

Methods

An initial cohort of 28 subjects was randomized (1:1:1:1) to receive B7A following an overnight fast at doses of 10⁸ or 10⁹ colony forming units (cfu) or a 90-minute fast at doses of 10⁹ or 10¹⁰ cfu. A second cohort included naïve and rechallenged subjects who had moderate-severe diarrhea and were given the target regimen. Immune responses to important ETEC antigens were assessed.

Results

Among subjects receiving 10⁸ cfu of B7A, overnight fast, or 10⁹ cfu, 90-minute fast, 42.9% (3/7) had moderate-severe diarrhea. Higher attack rates (71.4%; 5/7) occurred in subjects receiving 10⁹ cfu, overnight fast, or 10¹⁰ cfu, 90-minute fast. Upon rechallenge with 10⁹ cfu of B7A, overnight fast, 5/11 (45.5%) had moderate-severe diarrhea; the attack rate among concurrently challenge naïve subjects was 57.9% (11/19). Anti-CS6, O148 LPS and LT responses were modest across all groups.

Conclusions

An overnight fast enabled a reduction in the B7A inoculum dose; however, the attack rate was inconsistent and protection upon rechallenge was minimal.

Phosphodiesterase 5 (PDE5) restricts intracellular cGMP accumulation during enterotoxigenic Escherichia coli infection

Diarrhea caused by enterotoxigenic Escherichia coli (ETEC) has a continuing impact on residents and travelers in underdeveloped countries. Both heat-labile (LT) and heat-stable (ST) enterotoxins contribute to pathophysiology via induction of cyclic nucleotide synthesis, and previous investigations focused on intracellular signal transduction rather than possible intercellular second messenger signaling. We modeled ETEC infection in human jejunal enteroid/organoid monolayers (HEM) and evaluated cyclic nucleotide pools, finding that intracellular cAMP was significantly increased but also underwent apical export, whereas cGMP was minimally retained intracellularly and predominantly effluxed into the basolateral space. LT and virulence factors including EatA, EtpA, and CfaE promoted ST release and enhanced ST-stimulated cGMP production. Intracellular cGMP was regulated by MK-571-sensitive export in addition to degradation by phosphodiesterase 5. HEMs had limited ST-induced intracellular cGMP accumulation compared to T84 or Caco-2 models. Cyclic nucleotide export/degradation demonstrates additional complexity in the mechanism of ETEC infection and may redirect understanding of diarrheal onset.

Preclinical optimization of an enterotoxigenic Escherichia coli adjuvanted subunit vaccine using response surface design of experiments

Enterotoxigenic E. coli (ETEC) is a leading cause of moderate-to-severe diarrhoea. ETEC colonizes the intestine through fimbrial tip adhesin colonization factors and produces heat-stable and/or heat-labile (LT) toxins, stimulating fluid and electrolyte release leading to watery diarrhoea. We reported that a vaccine containing recombinant colonization factor antigen (CfaEB) targeting fimbrial tip adhesin of the colonization factor antigen I (CFA/I) and an attenuated LT toxoid (dmLT) elicited mucosal and systemic immune responses against both targets. Additionally, the toll-like receptor 4 ligand second-generation lipid adjuvant (TLR4-SLA) induced a potent mucosal response, dependent on adjuvant formulation. However, a combination of vaccine components at their respective individual optimal doses may not achieve the optimal immune profile. We studied a subunit ETEC vaccine prototype in mice using a response surface design of experiments (DoE), consisting of 64 vaccine dose-combinations of CfaEB, dmLT and SLA in four formulations (aqueous, aluminium oxyhydroxide, squalene-in-water stable nanoemulsion [SE] or liposomes containing the saponin Quillaja saponaria-21 [LSQ]). Nine readouts focusing on antibody functionality and plasma cell response were selected to profile the immune response of parenterally administered ETEC vaccine prototype. The data were integrated in a model to identify the optimal dosage of each vaccine component and best formulation. Compared to maximal doses used in mouse models (10 µg CfaEB, 1 µg dmLT and 5 µg SLA), a reduction in the vaccine components up to 37%, 60% and 88% for CfaEB, dmLT and SLA, respectively, maintained or even maximized immune responses, with SE and LSQ the best formulations. The DoE approach can help determine the best vaccine composition with a limited number of experiments and may accelerate development of multi-antigen/component ETEC vaccines.

Transcriptomic Study of Porcine Small Intestine Epithelial Cells Reveals Important Genes and Pathways Associated With Susceptibility to Escherichia coli F4ac Diarrhea

BACKGROUND

Diarrhea represents one of the most frequent major problems during piglets' neonatal and post-weaning periods leading to tremendous economic losses in the swine industry. Enterotoxigenic Escherichia coli (ETEC) F4 is regarded as the most important cause of diarrhea in piglets. However, some pigs are naturally resistant to those diarrheas caused by ETEC-F4, because they have no F4 receptors (F4R) on their small intestine epithelial cells that allow F4 fimbriae attachment. Thus, our study characterized a complete transcriptome of small intestine epithelial cells of Large White piglets using RNA-Seq. The aim of the study was to identify DEGs with regard to differences in the F4R phenotypes and SNP (C/T) genotypes at ITGB5 and important pathways associated with ETEC-F4ac susceptibility in small intestine epithelial cells of Large White piglets and derive molecular markers as a result of loss of F4acR in swine.

METHODS

A total of eight samples of small intestine epithelial cells obtained from Large White piglets (35 days old) used in this study were selected on the basis of two criteria. One was the adhesion phenotype to ETEC-F4ac fimbriae, and the other was the comparison of ITGB5 SNP (C > T) genotype sequences across all the samples. The samples were then divided into two groups, non-adhesive with CC genotype (n = 4), and adhesive with TT genotype (n = 4).

RESULTS

More down-regulated DEGs (p < 0.05, |log2FC| > 2) were detected in the comparison of non-adhesive vs. adhesive small intestine epithelial cells in the present study. Six genes, of which two (CNGA4, SLC25A31) exclusively expressed and four (HCN4, MYLK, KCNMA1, and KCNMB1) DEGs with up-regulation pattern in adhesive (F4R positive) pigs were involved in two pathways associated with diarrhea. The DEGs with up-regulation pattern in non-adhesive (F4R negative) pigs were mostly engaged in multiple immune response-related pathways.

CONCLUSION

The results provide insights on the biology of the phenotypes of F4R positive and negative pigs. One gene (MYLK) located on SSC13 locus for F4acR strongly support that it might have played a role in the adhesion phenotype which was obviously detected by adhesion assay in adhesive (F4R positive) group.

LTA1 and dmLT enterotoxin-based proteins activate antigen-presenting cells independent of PKA and despite distinct cell entry mechanisms

Enterotoxin-based proteins are powerful manipulators of mucosal immunity. The A1 domain of heat-labile enterotoxin from E. coli, or LTA1, is a newer adjuvant from this family under investigation for intranasal vaccines. Although LTA1 has been examined in mouse vaccination studies, its ability to directly stimulate immune cells compared to related adjuvant proteins has not been well explored. Here, we perform the first rigorous examination of LTA1’s effect on antigen presenting cells (APC) using a human monocyte cell line THP-1. To better understand LTA1’s stimulatory effects, we compared it to dmLT, or LT-R192G/L211A, a related AB₅ adjuvant in clinical trials for oral or parenteral vaccines. LTA1 and dmLT both activated APCs to upregulate MHC-II (HLA-DR), CD86, cytokine secretion (e.g., IL-1β) and inflammasome activation. The effect of LTA1 on surface marker changes (e.g., MHC-II) was highly dose-dependent whereas dmLT exhibited high MHC-II expression regardless of dose. In contrast, cytokine secretion profiles were similar and dose-dependent after both LTA1 and dmLT treatment. Cellular activation by LTA1 was independent of ganglioside binding, as pre-treatment with purified GM1 blocked the effect of dmLT but not LTA1. Unexpectedly, while activation of the inflammasome and cytokine secretion by LTA1 or dmLT was blocked by the protein kinase A inhibitor H89 (similar to previous reports), these responses were not inhibited by a more specific PKA peptide inhibitor or antagonist; thus Indicating that a novel and unknown mechanism is responsible for inflammasome activation and cytokine secretion by LT proteins. Lastly, LTA1 stimulated a similar cytokine profile in primary human monocytes as it did in THP1 cells, including IL-1β, IL-6, IL-8, MIP-1α, MIP-1β, and TNFα. Thus, we report that LTA1 protein programs a dendritic cell-like phenotype in APCs similar to dmLT in a mechanism that is independent of PKA activation and GM1 binding and entry.

Immunogenicity characterization of genetically fused or chemically conjugated heat-stable toxin toxoids of enterotoxigenic Escherichia coli in mice and pigs

Enterotoxigenic Escherichia coli (ETEC) producing type Ib heat-stable toxin (STa) are a main cause of children's diarrhea and travelers' diarrhea, thus STa needs to be targeted in ETEC vaccine development. However, because this 19-amino acid STa is poorly immunogenic, attempts to genetically fuse or chemically couple it to carrier proteins have been made to enhance STa immunogenicity. In this study, we selected one genetic fusion and one chemical conjugate to comparatively evaluate STa immunogenicity. The genetic fusion is 3xSTaN12S-mnLTR192G/L211A carrying three toxoid (STaN12S) genetically fused to a double mutant LT monomer (mnLTR192G/L211A); the chemical conjugate is BSA-STaA14T, which has toxoid STaA14T chemically coupled to bovine serum albumin (BSA). We immunized mice with the STa toxoid fusion and chemical conjugates, and examined antibody responses. Furthermore, we immunized pigs and evaluated derived antibodies for efficacy to passively provide protection against ETEC diarrhea using a piglet model. Data showed that mice subcutaneously immunized with BSA-STaA14T or 3xSTaN12S-mnLTR192G/L211A developed a strong anti-STa antibody, and the induced antibodies exhibited equivalent toxin-neutralizing activities. Pigs immunized with 3xSTaN12S-mnLTR192G/L211A or BSA-STaA14T developed similar levels of anti-STa antibodies; piglets with passively acquired antibodies induced by the genetic fusion appeared better protected against STa + ETEC. Results from the current study indicate that the fusion and conjugate approaches are viable options for facilitating STa immunogenicity and developing ETEC vaccines.

Intradermal or Sublingual Delivery and Heat-Labile Enterotoxin Proteins Shape Immunologic Responses to a CFA/I Fimbria-Derived Subunit Antigen Vaccine against Enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is a major cause of infectious diarrhea in children, travelers, and deployed military personnel. As such, development of a vaccine would be advantageous for public health. One strategy is to use subunits of colonization factors combined with antigen/adjuvant toxoids as an ETEC vaccine. Here, we investigated the intradermal (i.d.) or sublingual (s.l.) delivery of CFA/I fimbrial antigens, including CfaEB and a CfaE-heat-labile toxin B subunit (LTB) chimera admixed with double mutant heat-labile toxin (LT) LT-R192G/L211A (dmLT). In addition, we compared dmLT with other LT proteins to better understand the generation of adjuvanted fimbrial and toxoid immunity as well as the influence on any local skin reactogenicity. We demonstrate that immunization with dmLT admixed with CfaEB induces robust serum and fecal antibody responses to CFA/I fimbriae and LT but that i.d. formulations are not optimal for s.l. delivery. Improved s.l. vaccination outcomes were observed when higher doses of dmLT (1 to 5 μg) were admixed with CfaEB or, even better, when a CfaE-LTB chimera antigen was used instead. Serum anti-CFA/I total antibodies, detected by enzyme-linked immunosorbent assay, were the best predictor of functional antibodies, based on the inhibition of red blood cell agglutination by ETEC. Immunization with other LT proteins or formulations with altered B-subunit binding during i.d. immunization (e.g., by addition of 5% lactose, LTA1, or LT-G33D) minimally altered the development of antibody responses and cytokine recall responses but reduced skin reactogenicity at the injection site. These results reveal how formulations and delivery parameters shape the adaptive immune responses to a toxoid and fimbria-derived subunit vaccine against ETEC.

Development of an enterotoxigenic Escherichia coli vaccine based on the heat-stable toxin

Infection with enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrhea-related illness and death among children under 5 years of age in low– and middle-income countries (LMIC). Recent studies have found that it is the ETEC subtypes that produce the heat-stable enterotoxin (ST), irrespective of whether they also secrete the heat-labile enterotoxin (LT), which contribute most importantly to the disease burden in children from LMIC. Therefore, adding an ST toxoid would importantly complement ongoing ETEC vaccine development efforts. The ST’s potent toxicity, its structural similarity to the endogenous peptides guanylin and uroguanylin, and its poor immunogenicity have all complicated the advancement of ST-based vaccine development. Recent remarkable progress, however, including the unprecedented screening for optimal ST mutants, mapping of cross-reacting ST epitopes and improved ST-carrier coupling strategies (bioconjugation and genetic fusion), enables the rational design of safe, immunogenic, and well-defined ST-based vaccine candidates.

Enterotoxigenic Escherichia coli-blood group A interactions intensify diarrheal severity

Enterotoxigenic Escherichia coli (ETEC) infections are highly prevalent in developing countries, where clinical presentations range from asymptomatic colonization to severe cholera-like illness. The molecular basis for these varied presentations, which may involve strain-specific virulence features as well as host factors, has not been elucidated. We demonstrate that, when challenged with ETEC strain H10407, originally isolated from a case of cholera-like illness, blood group A human volunteers developed severe diarrhea more frequently than individuals from other blood groups. Interestingly, a diverse population of ETEC strains, including H10407, secrete the EtpA adhesin molecule. As many bacterial adhesins also agglutinate red blood cells, we combined the use of glycan arrays, biolayer inferometry, and noncanonical amino acid labeling with hemagglutination studies to demonstrate that EtpA is a dominant ETEC blood group A-specific lectin/hemagglutinin. Importantly, we have also shown that EtpA interacts specifically with glycans expressed on intestinal epithelial cells from blood group A individuals and that EtpA-mediated bacterial-host interactions accelerate bacterial adhesion and effective delivery of both the heat-labile and heat-stable toxins of ETEC. Collectively, these data provide additional insight into the complex molecular basis of severe ETEC diarrheal illness that may inform rational design of vaccines to protect those at highest risk.

Heat-Labile Enterotoxin-Induced PERK-CHOP Pathway Activation Causes Intestinal Epithelial Cell Apoptosis

Enterotoxigenic Escherichia coli (ETEC) is a leading cause of diarrhea among children and travelers in developing countries, and heat-labile enterotoxin (LT) is one of the most important virulence factors. The pathogenesis of and virulence factors associated with ETEC have been well-characterized; however, the extent to which ETEC damages host cells remains unclear. In this study, we found that LT could induce decreases in intestinal epithelial cell viability and induce apoptosis in a dose- and time- dependent manner in both HCT-8 and Caco-2 cells. We analyzed the expression profiles of apoptosis-related proteins via protein array technology and found that Bax, p-p53(S46), cleaved caspase-3, and TNFRI/TNFRSF1A expression levels were significantly up-regulated in wild-type ETEC- but not in ΔLT ETEC-infected HCT-8 cells. Bax is essential for endoplasmic reticulum (ER) stress-triggered apoptosis, and our RNAi experiments showed that the PERK-eIF2-CHOP pathway and reactive oxygen species (ROS) are also main participants in this process. LT-induced ROS generation was decreased in CHOP-knockdown HCT-8 cells compared to that in control cells. Moreover, pretreatment with the ROS inhibitor NAC down-regulated GRP78, CHOP, Bim, and cleaved caspase-3 expression, resulting in a reduction in the apoptosis rate from 36.2 to 20.3% in LT-treated HCT-8 cells. Furthermore, ROS inhibition also attenuated LT-induced apoptosis in the small intestinal mucosa in the ETEC-inoculation mouse model.

Effects of Ex Vivo Infection with ETEC on Jejunal Barrier Properties and Cytokine Expression in Probiotic-Supplemented Pigs

BACKGROUND AND AIM

Enterotoxigenic Escherichia coli (ETEC) strains are involved in piglet post-weaning diarrhea. Prophylactic measures including probiotics have been examined in infection experiments with live piglets. In the present study, we have tested whether the early effects of ETEC infection can also be evoked and studied in a model in which ETEC is added to whole mucosal tissues ex vivo, and whether this response can be modulated by prior supplementation of the piglets with probiotics.

METHODS

Jejunal barrier and transport properties of Enterococcus faecium-supplemented or control piglets were assessed in Ussing chambers. Part of the epithelia was challenged with an ETEC strain at the mucosal side. Fluxes of fluorescein as a marker of paracellular permeability, and the expression of selected tight junction (TJ) proteins and of proinflammatory cytokines were measured.

RESULTS

The addition of ETEC ex vivo induced an increase in transepithelial resistance peaking in the first 2 h with a concomitant reduction in fluorescein fluxes, indicating tightening effects on barrier function. The response of short-circuit current after stimulation with PGE₂ or glucose was reduced in epithelia treated with ETEC. ETEC induced a decrease in the TJ protein claudin-4 in the control diet group after 280 min and an increase in the mRNA expression of the proinflammatory cytokines interleukin-8 and TNF-α in both groups after 180 min.

CONCLUSIONS

The addition of ETEC ex vivo affected barrier function and transport properties of the jejunal tissues and enhanced cytokine expression. The differences in claudin-4 expression in the jejunum might indicate a beneficial effect of E. faecium prefeeding.

Foodborne enterotoxigenic Escherichia coli: from gut pathogenesis to new preventive strategies involving probiotics

Enterotoxigenic Escherichia coli (ETEC) are a major cause of traveler's diarrhea and infant mortality in developing countries. Given the rise of antibiotic resistance worldwide, there is an urgent need for the development of new preventive strategies. Among them, a promising approach is the use of probiotics. Although many studies, mostly performed under piglet digestive conditions, have shown the beneficial effects of probiotics on ETEC by interfering with their survival, virulence or adhesion to mucosa, underlying mechanisms remain unclear. This review describes ETEC pathogenesis, its modulation by human gastrointestinal cues as well as novel preventive strategies with a particular emphasis on probiotics. The potential of in vitro models simulating human digestion in elucidating probiotic mode of action will be discussed.

Campomanesia adamantium Peel Extract in Antidiarrheal Activity: The Ability of Inhibition of Heat-Stable Enterotoxin by Polyphenols

Campomanesia adamantium (Myrtaceae) is a medicinal plant distributed in Brazilian Cerrado. Different parts of this plant are used in popular medicine for treatment of several diseases like fever, diarrhea, hypercholesterolemia and rheumatism. The aim of this work was to evaluate the inhibition of heat-stable enterotoxin type A (STa) by gallic acid present in the peel of C. adamantium fruit and assays to assess the antidiarrheal activity, anti-inflammatory and cytotoxic properties of peel extract using the T84 cell line model. The possible inhibition exerted by the gallic acid of the peel extract on the STa peptide was inferred by molecular dynamics simulations. The antidiarrheal effects were investigated measuring cGMP accumulation in cells after stimulation by STa toxin and antibacterial activity was assessed. The anti-inflammatory activity was assessed by inhibition of COX-1 and COX-2. MTT and LDH assays were used to evaluate any possible cytotoxic action while the CyQUANT test was used to investigate the effect on cell proliferation. A representation showing how the possible interactions between STa and the gallic acid of the extract might reduce the action of the enterotoxin is presented. C. adamantium peel extract significantly decreased the levels of cGMP in T84 cells. However, no effect on the species of microorganisms was observed. The extract also inhibited COX-1 (IC₅₀ 255.70 ± 0.04 ng/mL) and COX-2 (IC₅₀ 569.50 ± 0.11 ng/mL) enzymes. Cytotoxicity assay have shown significant changes in cells treated with the extract, which inhibited the cell proliferation until 72 hours of treatment. Direct interactions of phenolic compounds present in the extract with the STa toxin may limit its activity. Curative effect in the diarrhea treatment and its anti-inflammatory action is based on the pharmacological properties, mechanism of action of the C. adamantium peel extract, and no toxic effects of the peel extract presented on this work.

Electron Acceptors Induce Secretion of Enterotoxigenic Escherichia coli Heat-Labile Enterotoxin under Anaerobic Conditions through Promotion of GspD Assembly

Heat-labile enterotoxin (LT), the major virulence factor of enterotoxigenic Escherichia coli (ETEC), can lead to severe diarrhea and promotes ETEC adherence to intestinal epithelial cells. Most previous in vitro studies focused on ETEC pathogenesis were conducted under aerobic conditions, which do not reflect the real situation of ETEC infection because the intestine is anoxic. In this study, the expression and secretion of LT under anaerobic or microaerobic conditions were determined; LT was not efficiently secreted into the supernatant under anaerobic or microaerobic conditions unless terminal electron acceptors (trimethylamine N-oxide dihydrate [TMAO] or nitrate) were available. Furthermore, we found that the restoration effects of TMAO and nitrate on LT secretion could be inhibited by amytal or ΔtorCAD and ΔnarG E. coli strains, indicating that LT secretion under anaerobic conditions was dependent on the integrity of the respiratory chain. At the same time, electron acceptors increase the ATP level of ETEC, but this increase was not the main reason for LT secretion. Subsequently, the relationship between the integrity of the respiratory chain and the function of the type II secretion system was determined. The GspD protein, the secretin of ETEC, was assembled under anaerobic conditions and was accompanied by LT secretion when TMAO or nitrate was added. Our data also demonstrated that TMAO and nitrate could not induce the GspD assembly and LT secretion in ΔtorCAD and ΔnarG strains, respectively. Moreover, GspD assembly under anaerobic conditions was assisted by the pilot protein YghG.

Status of vaccine research and development for enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is one of the most common bacterial causes of diarrhea-associated morbidity and mortality, particularly among infants and young children in developing countries. Still, the true impact on child and traveler health is likely underestimated. There are currently no licensed vaccines for ETEC, but studies indicate high public health impact, cost-effectiveness, and feasibility of immune protection through vaccination. ETEC vaccine development remains a World Health Organization priority. Traditionally, ETEC vaccine development efforts have focused on inducing antitoxin and anticolonization antigen immunity, as studies indicate that antibodies against both antigen types can contribute to protection and thus have potential for vaccines. Leading cellular vaccine candidates are ETVAX (a mixture of four inactivated strains) and ACE527 (a mixture of three live attenuated strains), both of which have been found to be safe and immunogenic in Phase 1/2 trials. ETVAX is the furthest along in development with descending-age studies already underway in Bangladesh. Other ETEC vaccine candidates based on protein subunits, toxoids (both LT and ST), or novel, more broadly conserved ETEC antigens are also under development. Of these, a protein adhesin-based subunit approach is the most advanced. Impact and economic models suggest favorable vaccine cost-effectiveness, which may help expand market interest in ETEC vaccines. Combination vaccine formulations may help improve the economic case for development and use, and better point-of-care diagnostics will help to raise awareness of the true health burden of ETEC and highlight the potential public health benefit of ETEC vaccine introduction. Better diagnostics and vaccine demand forecasting will also improve vaccine development financing and support accelerated uptake once a licensed vaccine becomes available.

The different ecological niches of enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is a water and food-borne pathogen that infects the small intestine of the human gut and causes diarrhoea. Enterotoxigenic E. coli adheres to the epithelium by means of colonization factors and secretes two enterotoxins, the heat labile toxin and/or the heat stable toxin that both deregulate ion channels and cause secretory diarrhoea. Enterotoxigenic E. coli as all E. coli, is a versatile organism able to survive and grow in different environments. During transmission and infection, ETEC is exposed to various environmental cues that have an impact on survivability and virulence. The ability to cope with exposure to different stressful habitats is probably shaping the pool of virulent ETEC strains that cause both endemic and epidemic infections. This review will focus on the ecology of ETEC in its different habitats and interactions with other organisms as well as abiotic factors.