Enterotoxigenic Escherichia coli (ETEC) vaccines: Priority activities to enable product development, licensure, and global access

Genome-based assessment of antimicrobial resistance of Escherichia coli recovered from diseased swine in eastern China for a 12-year period

The global rise of antimicrobial resistance (AMR), driven by antibiotic use in healthcare and agriculture, poses a major public health threat. While AMR in clinical settings is well studied, there is a gap in understanding the resistance profiles of Escherichia coli from diseased livestock, particularly regarding zoonotic transmission. This study analyzes 114 E. coli isolates from diseased swine over 12 years, revealing that 99.12% were multidrug-resistant. Resistance was highest for ampicillin and amoxicillin/clavulanic acid (100%), followed by ciprofloxacin (96.49%) and tetracycline (94.74%). Furthermore, 21.05% of isolates were resistant to colistin, and 1.75% to tigecycline. A total of 76 antimicrobial resistance genes (ARGs) were identified, with mcr-1 found in 18.42%, mcr-3 in 4.39%, and tet(X4) in 1.75%. Significant co-occurrence of ARGs and plasmids suggests potential for co-selective dissemination. This study is the first to report enterotoxigenic E. coli (ETEC) strains carrying both mcr-1 and mcr-3 genes. After the 2017 colistin ban in China, mcr-1 detection rates significantly decreased, while florfenicol resistance rates increased in 2018-2021 (94.29%) compared to 2010-2017 (79.55%). This work provides valuable insights into the AMR profiles of E. coli from diseased swine and highlights trends that can inform strategies for monitoring and controlling public health risks associated with zoonotic E. coli transmission.IMPORTANCEThis study highlights the critical role of diseased and deceased swine in the spread of antimicrobial resistance (AMR), providing new insights into the transmission of resistance genes in zoonotic contexts. By analyzing E. coli from diseased swine, we identify key resistance genes such as mcr-1, mcr-3, and tet(X4), which pose significant public health risks, especially regarding last-resort antibiotics like colistin. Moreover, the study identifies novel transmission patterns of mcr genes, including ETEC strains carrying the mcr-3 gene and strains harboring both mcr-1 and mcr-3 genes. The role of plasmids in horizontal gene transfer is also revealed, facilitating rapid AMR spread across species. The long-term persistence of resistant strains highlights the challenges in controlling AMR in livestock. These findings underscore the need for enhanced surveillance and a One Health approach to mitigate AMR risks across animal, human, and environmental health.

Parenteral vaccination with recombinant EtpA glycoprotein impairs enterotoxigenic E. coli colonization

Enterotoxigenic E. coli (ETEC) causes hundreds of millions of cases of acute diarrheal illness in low- and middle-income regions, disproportionately in young children. To date, there is no licensed, broadly protective vaccine against these common but antigenically heterogeneous pathogens. One of the more highly conserved antigens of ETEC, EtpA, is an extracellular glycoprotein adhesin that preferentially binds to A blood group glycans on intestinal epithelia. EtpA contributes to increased severity of illness in A blood group individuals, elicits robust serologic and fecal antibody responses following infection, and has been associated with protection against subsequent infection. However, its utility as a protective antigen needs further examination. In the present studies, we examined whether parenteral vaccination with recombinant EtpA (rEtpA) could afford protection against intestinal colonization in a murine model of ETEC infection. Here, we demonstrate that intramuscular vaccination with rEtpA, adjuvanted with double mutant LT (dmLT), primes IgG predominant mucosal antibody responses to ETEC challenge. Notably, however, both antibody levels and avidity, as well as protection, were dependent on the vaccination schedule. Likewise, through electron microscopy polyclonal epitope mapping (EMPEM), we observed a different repertoire of epitopes targeted by antibodies after a more protracted vaccination schedule. Next, we explored the utility of IM immunization with alum-adjuvanted rEtpA. This elicited strong serologic and fecal IgG responses. Although accompanied by negligible IgA mucosal responses, EtpA alum-adjuvanted IM vaccination nevertheless protected against ETEC intestinal colonization. Collectively, these data suggest that EtpA could expand the portfolio of antigens targeted in ETEC subunit vaccine development.

Global, regional, and national age-sex-specific burden of diarrhoeal diseases, their risk factors, and aetiologies, 1990-2021, for 204 countries and territories: a systematic analysis for the Global Burden of Disease Study 2021

BACKGROUND

Diarrhoeal diseases claim more than 1 million lives annually and are a leading cause of death in children younger than 5 years. Comprehensive global estimates of the diarrhoeal disease burden for specific age groups of children younger than 5 years are scarce, and the burden in children older than 5 years and in adults is also understudied. We used results from the Global Burden of Diseases, Injuries, and Risk Factors Study 2021 to assess the burden of, and trends in, diarrhoeal diseases overall and attributable to 13 pathogens, as well as the contributions of associated risk factors, in children and adults in 204 countries and territories from 1990 to 2021.

METHODS

We used the Cause of Death Ensemble modelling strategy to analyse vital registration data, verbal autopsy data, mortality surveillance data, and minimally invasive tissue sampling data. We used DisMod-MR (version 2.1), a Bayesian meta-regression tool, to analyse incidence and prevalence data identified via systematic reviews, population-based surveys, and claims and inpatient data. We calculated diarrhoeal disability-adjusted life-years (DALYs) as the sum of years of life lost (YLLs) and years lived with disability (YLDs) for each location, year, and age-sex group. For aetiology estimation, we used a counterfactual approach to quantify population-attributable fractions (PAFs). Additionally, we estimated the diarrhoeal disease burden attributable to the independent effects of risk factors using the comparative risk assessment framework.

FINDINGS

In 2021, diarrhoeal diseases caused an estimated 1·17 million (95% uncertainty interval 0·793-1·62) deaths globally, representing a 60·3% (50·6-69·0) decrease since 1990 (2·93 million [2·31-3·73] deaths). The most pronounced decline was in children younger than 5 years, with a 79·2% (72·4-84·6) decrease in diarrhoeal deaths. Global YLLs also decreased substantially, from 186 million (147-221) in 1990 to 51·4 million (39·9-65·9) in 2021. In 2021, an estimated 59·0 million (47·2-73·2) DALYs were attributable to diarrhoeal diseases globally, with 30·9 million (23·1-42·0) of these affecting children younger than 5 years. Leading risk factors for diarrhoeal DALYs included low birthweight and short gestation in the neonatal age groups, child growth failure in children aged between 1-5 months and 2-4 years, and unsafe water and poor sanitation in older children and adults. We estimated that the removal of all evaluated diarrhoeal risk factors would reduce global DALYs from 59·0 million (47·2-73·2) to 4·99 million (1·99-10·0) among all ages combined. Globally in 2021, rotavirus was the predominant cause of diarrhoeal deaths across all ages, with a PAF of 15·2% (11·4-20·1), followed by norovirus at 10·6% (2·3-17·0) and Cryptosporidium spp at 10·2% (7·03-14·3). In children younger than 5 years, the fatal PAF of rotavirus was 35·2% (28·7-43·0), followed by Shigella spp at 24·0% (15·2-37·9) and adenovirus at 23·8% (14·8-36·3). Other pathogens with a fatal PAF greater than 10% in children younger than 5 years included Cryptosporidium spp, typical enteropathogenicEscherichia coli, and enterotoxigenic E coli producing heat-stable toxin.

INTERPRETATION

The substantial decline in the global burden of diarrhoeal diseases since 1990, particularly in children younger than 5 years, supports the effectiveness of health interventions such as oral rehydration therapy, enhanced water, sanitation, and hygiene (WASH) infrastructure, and the introduction and scale-up of rotavirus vaccination. Targeted interventions and preventive measures against key risk factors and pathogens could further reduce this burden. Continued investment in the development and distribution of vaccines for leading pathogens remains crucial.

FUNDING

Bill & Melinda Gates Foundation.

Benzoic acid as a dietary supplement mitigates inflammation and intestinal injury in acute enterotoxigenic Escherichia coli-infected mice without adverse effects in healthy mice

Benzoic acid is a naturally occurring compound found in fruits and is also commercially synthesized as an additive in the food, feed, and pharmaceutical industries. This study investigated the effects of benzoic acid as a dietary supplement on inflammation and intestinal injury in acute Escherichia coli (ETEC)-infected or healthy mice. Thirty-six BALB/c mice were divided into three groups, with 12 mice in each group for a 16-day feeding trial. In group 1, mice were fed a basal diet, six mice were sacrificed, and six mice were intraperitoneally injected with phosphate-buffered saline on day 15. Groups 2 and 3 were fed a basal diet and a diet containing 0.6% benzoic acid, respectively. Half of the mice in each group were sacrificed, while the others were intraperitoneally injected with ETEC on day 15. The results indicated that benzoic acid had no adverse effects on healthy mice regarding growth, organ indices, inflammation, intestinal injury parameters, and cecal short-chain fatty acid levels. Importantly, benzoic acid reduced inflammation in ETEC-infected mice, as evidenced by decreased serum IL-1β, TNF-α, and INF-γ levels, along with increased jejunal TLR-2 and MyD88 mRNA expression. Besides, benzoic acid mitigated intestinal injury in ETEC-infected mice by increasing the jejunal villus height (VH) and the ratio of VH to crypt depth, elevating jejunal Occludin mRNA levels, decreasing serum D-lactate and diamine oxidase levels, and increasing the cecal acetic acid level. 16s rRNA sequencing revealed that benzoic acid altered the β-diversity of ETEC-infected mice and increased the abundances of Erysipelotrichaceae, Faecalibaculum, and Turicibacter in their gut microbiota. Spearman correlation analysis further indicated that the protective effects of benzoic acid against ETEC infection were closely linked to specific gut microbiota, namely Erysipelotrichaceae, Faecalibaculum, Bifidobacterium, and Limosilactobacillus. Collectively, these findings suggest that benzoic acid could serve as a safe dietary supplement for healthy mice and may alleviate inflammation and intestinal injury in mice with acute ETEC infection.

Association of Escherichia coli pathotypes with fecal markers of enteropathy and nutritional status among underweight adults in Bangladesh

Introduction

Environmental enteric dysfunction (EED), a subclinical intestinal disorder, is characterized by chronic fecal-oral exposure to entero-pathogens and could be diagnosed by measuring non-invasive biomarkers. Escherichia coli is the one of the key bacterial enteric pathogens that drives EED, but there is a lack of information on the E. coli pathotypes in relation to the biomarkers of EED in malnourished adults. Here, we intended to measure the possible association of these pathotypes with EED biomarkers and nutritional status of adults residing in a slum in Bangladesh.

Method

Fecal samples were collected from 524 malnourished adults (BMI ≤18.5 kg/m2) living in a slum-setting in Dhaka from March 2016 to September 2019 and analyzed by TaqMan Array Card assays to evaluate the presence of E. coli pathotypes and other entero-pathogens. The multivariable linear regression model was used to assess the association.

Results

In these malnourished adults, the most prevalent pathotype of E. coli was EAEC (61.7%) and the least prevalent was STEC (6.7%). The prevalence of atypical EPEC, ETEC and Shigella/EIEC were 52%, 48.9% and 45.1% respectively. The infection with atypical EPEC had significant positive association with levels of Myeloperoxidase (b = 0.38; 95% CI = 0.11, 0.65; p-value = 0.006). Similarly, a significantly higher concentration of alpha-1-antitrypsin (b = 0.13; 95% CI = 0.03, 0.22; p-value = 0.011) was found in the STEC-infected adults. However, no notable association was found between the E. coli pathotypes and nutritional status of these adult participants. Moreover, Plesiomonas infected adults were more likely to be infected with EAEC (p-value = 0.017), ETEC (p-value <0.001) and STEC (pvalue = 0.002). Significant coinfection was also detected among the pathotypes and other entero-pathogens such as Giardia, Ascaris, Campylobacter, Salmonella, Enterocytozoon bieneusi, and Adenovirus.

Discussion

The study results imply that there is an influence of particular E. coli pathotypes (EPEC and STEC) on intestinal inflammation and gut permeability of the malnourished Bangladeshi adults, but no association with nutritional status is found. Potential pathogenicity of the E. coli pathotypes is also observed when co-infection with other pathogens exists in these adults.

Conserved antigens for enteric vaccines

Enterotoxigenic Escherichia coli (ETEC), Shigella, and Campylobacter have been identified as major causes of diarrheal diseases worldwide. In addition to overt disease and death, they are responsible for stunting in children with the risk of lifelong consequences on health and economic opportunities. All three of these bacterial pathogens, which collectively account for approximately 30 % of the cases of diarrheal diseases, are recognized as antimicrobial resistance (AMR) threats. In spite of the dangers these pathogens represent for both children and adults, there is as yet no licensed vaccine available for any of them. Fortunately, much has been accomplished to identify conserved antigens against each of these pathogens so that now relatively simple vaccines have the potential to be developed into multi-pathogen vaccines which could have a major impact on reduction of diarrheal diseases. Conserved antigens may be used even more efficiently if consolidated and expressed on a cellular vector or as part of a conjugate vaccine. A new mucosal adjuvant, double mutant heat-labile toxin (dmLT), has been shown to not only be among the conserved antigens against ETEC, but to also have properties which drive robust mucosal and systemic immune responses for antigens given orally or intramuscularly. Conserved antigens and the strategies for their use such as co-administration with dmLT will be presented in this review.

Use of a TaqMan Array Card for identification of enterotoxins and colonization factors directly from stool samples in an enterotoxigenic E. coli vaccine study

Enterotoxigenic Escherichia coli (ETEC) is a leading cause of childhood and travelers' diarrhea. The vaccine candidate ETVAX encompasses several ETEC colonization factors (CFs) with a hybrid LT (heat-labile toxin)/cholera toxin B subunit adjuvanted with a double-mutant LT. Stool samples from a Phase 2b ETVAX trial were tested by a PCR-based customized TaqMan Array Card (TAC), including three ETEC toxin genes (LT and heat-stable toxins, STh and STp) and 18 ETEC CFs. Stool samples were also tested with the molecular platform Amplidiag and culture, followed by GM1-enzyme-linked immunosorbent assay (ELISA) and inhibition GM1-ELISA for LT and ST and dot blot for CFs of ETECs identified among six culture isolates (maximum). Compared with Amplidiag, TAC yielded 89.4% sensitivity (320/358) and 96.4% specificity (405/420) for ETEC detection. The two methods demonstrated a good quantitative correlation (quantification cycle R2 = 0.827, P < 0.05). Compared with culture, TAC and Amplidiag each exhibited 96.8% (184/190) sensitivity and identified an additional of 151 and 174 PCR positives in 588 culture-negative stools, respectively. The concordance of stool TAC versus ELISA of ETEC colonies for LT and STh/STp was 85.5% (165/193). TAC demonstrated 98% sensitivity and 92% specificity versus the dot blot results of 793 colonies for the ETVAX CFs CFA/I, CS3, CS5, and CS6. Overall ETEC was detected by TAC in 335 (43.1%) and by Amplidiag in 358 (46.0%) of specimens compared to 190 (24.4%) by culture. We conclude that molecular diagnostic approaches of TAC or Amplidiag increase the detection of ETEC compared with culture, and TAC can also provide vaccine-subtype ETEC data.CLINICAL TRIALSThis study was registered with ClinicalTrials.gov as NCT03729219.IMPORTANCEEnterotoxigenic Escherichia coli (ETEC) is an important cause of childhood and travelers' diarrhea. Vaccines in development utilize specific toxins and colonization factors (CFs) as antigens. Therefore, clinical microbiologic diagnostic methods are needed to discriminate specific toxins and CFs, both for vaccine trials and to guide epidemiology. In this work, we assessed the diagnostic performance of several methods for ETEC: a PCR-based customized TaqMan Array Card (TAC) and the molecular platform Amplidiag on stool and E. coli culture, followed by GM1-enzyme-linked immunosorbent assay for toxins and dot blot for CFs. Stool samples from a Phase 2b ETEC vaccine trial were used. Overall, ETEC was detected by TAC in 335 (43.1%) and by Amplidiag in 358 samples (46.0%) compared to 190 (24.4%) by culture. TAC additionally provided CF data with 98% sensitivity and 92% specificity. We conclude that the molecular diagnostic approaches of TAC or Amplidiag increase the detection of ETEC compared with culture.

Targeting Enterotoxins: Advancing Vaccine Development for Enterotoxigenic Escherichia coli ETEC

Enterotoxigenic Escherichia coli (ETEC) is a major cause of diarrheal disease worldwide, particularly in children in low- and middle-income countries. Its ability to rapidly colonize the intestinal tract through diverse colonization factors and toxins underpins its significant public health impact. Despite extensive research and several vaccine candidates reaching clinical trials, no licensed vaccine exists for ETEC. This review explores the temporal and spatial coordination of ETEC virulence factors, focusing on the interplay between adherence mechanisms and toxin production as critical targets for therapeutic intervention. Advancements in molecular biology and host-pathogen interaction studies have uncovered species-specific variations and cross-reactivity between human and animal strains. In particular, the heat-labile (LT) and heat-stable (ST) toxins have provided crucial insights into molecular mechanisms and intestinal disruption. Additional exotoxins, such as EAST-1 and hemolysins, further highlight the multifactorial nature of ETEC pathogenicity. Innovative vaccine strategies, including multiepitope fusion antigens (MEFAs), mRNA-based approaches, and glycoconjugates, aim to enhance broad-spectrum immunity. Novel delivery methods, like intradermal immunization, show promise in eliciting robust immune responses. Successful vaccination against ETEC will offer an effective and affordable solution with the potential to greatly reduce mortality and prevent stunting, representing a highly impactful and cost-efficient solution to a critical global health challenge.

Safety and immunogenicity in humans of enterotoxigenic Escherichia coli double mutant heat-labile toxin administered intradermally

Enterotoxigenic Escherichia coli (ETEC) diarrhea is associated with a high burden of disease globally, for which no licensed vaccine is available. A Phase 1, double-blind, dose-escalation (0.1-2.0 µg) study was conducted to evaluate the safety and immunogenicity of double mutant heat-labile toxin LTR192G/L211A (dmLT) delivered intradermally (ID) to healthy adults. Subjects received up to three immunizations at three-week intervals. The vaccine was safe, although it induced mild local and some gastrointestinal adverse events, as well as frequent hyperpigmentation at the injection site. High levels of serum IgG and IgA, LT neutralizing antibodies, and IgG and IgA antibodies in lymphocyte supernatant were elicited post-vaccination, most prominently at the largest dose (2.0 μg). Rates of responses were the highest in subjects who received the largest dose (2.0 μg) and multiple immunizations. The ETEC dmLT vaccine was safe and highly immunogenic, inducing long-lasting systemic and mucosal responses when administered by the ID route. Trial registration Clinical Trials NCT02531685.

Proportions of IgA antibodies targeting glycosylated epitopes of secreted Escherichia coli mucinase YghJ in initial plasmablast response differ from salivary and intestinally secreted IgA

Mucosal infections normally cause an immune response including activation of antigen-specific B cells in regional mucosa-associated lymphoid tissue. After recirculation of plasmablasts, and maturation at mucosal surfaces or bone marrow, plasma cells produce secretory or systemic IgA. It remains uncertain to what extent secretory and systemic IgA share the same target specificities. For vaccine candidate optimization, it is important to know whether IgA targeting of glycosylated epitopes of a protein antigen vary between mucosal and systemic sites. We evaluated glycosylated epitope specificity of systemic and mucosally secreted IgA against YghJ, a potential vaccine candidate antigen secreted by most pathogenic Escherichia coli. IgA from intestinal lavage, saliva, serum, and blood-derived antibody in lymphocyte supernatants (ALS) were collected from 21 volunteers following experimental infection with enterotoxigenic E. coli. Methods for preparing IgA from saliva and ALS were developed, and multiplex bead flow cytometric immunoassays were used to determine levels of IgA targeting natively glycosylated YghJ and estimating what proportion of these antibodies specifically targeted glycosylated epitopes. Following infection, anti-YghJ IgA levels increased substantially for most volunteers across all four specimen types. Target specificity of ALS IgA correlated well with serum IgA, but not with mucosally secreted IgA. Furthermore, glycosylation-specific proportion of salivary IgA was higher than, and did not correlate with, intestinally secreted IgA. These results indicate a new degree of complexity to our understanding of epitope-targeting and tissue specificity of mucosal antibody responses. Our findings also suggest that all features of an intestinal IgA response may not be well reflected in serum, saliva, or ALS, which are commonly used proxy specimens for evaluating intestinal immune responses.

Natural anti-adhesive components against pathogenic bacterial adhesion and infection in gastrointestinal tract: case studies of Helicobacter pylori, Salmonella enterica, Clostridium difficile, and diarrheagenic Escherichia coli

Antimicrobial resistance (AMR) poses a global public health concern. Recognizing the critical role of bacterial adhesion in pathogenesis of infection, anti-adhesive therapy emerges as a promising approach to impede initial bacterial attachment, thus preventing pathogenic colonization and infection. Natural anti-adhesive agents derived from food sources are generally safe and have the potential to inhibit the emergence of resistant bacteria. This comprehensive review explored diverse natural dietary components exhibiting anti-adhesive activities against several model enteric pathogens, including Helicobacter pylori, Salmonella enterica, Clostridium difficile, and three key diarrheagenic Escherichia coli (i.e., enterotoxigenic E. coli, enteropathogenic E. coli, and enterohemorrhagic E. coli). Investigating various anti-adhesive products will advance our understanding of current research of the field and inspire further development of these agents as potential nutraceuticals or adjuvants to improve the efficacy of conventional antibiotics.

A tetravalent peptide efficiently inhibits the intestinal toxicity of heat-labile enterotoxin by targeting the receptor-binding region of the B-subunit pentamer

Infection by enterotoxigenic Escherichia coli (ETEC) causes severe watery diarrhea and dehydration in humans. Heat-labile enterotoxin (LT) is a major virulence factor produced by ETEC. LT is one of AB5-type toxins, such as Shiga toxin (Stx) and cholera toxin (Ctx), and the B-subunit pentamer is responsible for high affinity binding to the LT-receptor, ganglioside GM1, through multivalent interaction. In this report, we found that Glu51 of the B-subunit plays an essential role in receptor binding compared with other amino acids, such as Glu11, Arg13, and Lys91, all of which were previously shown to be involved in the binding. By targeting Glu51, we identified four tetravalent peptides that specifically bind to the B-subunit pentamer with high affinity by screening tetravalent random-peptide libraries, which were tailored to bind to the B-subunit through multivalent interaction. One of these peptides, GGR-tet, efficiently inhibited the cell-elongation phenotype and the elevation of cellular cAMP levels, both induced by LT. Furthermore, GGR-tet markedly inhibited LT-induced fluid accumulation in the mouse ileum. Thus, GGR-tet represents a novel therapeutic agent against ETEC infection.

Enterotoxigenic Escherichia coli in Blantyre, Malawi

We announce the deposition of the first two enterotoxigenic Escherichia coli (ETEC) genomes from Malawi. They were isolated from the faeces of asymptomatically infected children obtained in 2014. Both genomes encode the porcine variant of the heat-labile toxin and no known ETEC colonization factors.

Predominance of enterotoxigenic Escherichia coli among ESBL/plasmid-mediated AmpC-producing strains isolated from diarrheic foals: a public health concern

BACKGROUND

The upsurge of diarrheagenic E. coli pathotypes carrying extended-spectrum beta-lactamases (ESBLs)/plasmid-mediated AmpC β-lactamase (pAmpC) among animals constitutes an emerging threat for humans and animals. This study investigated the burden of ESBL-/pAmpC-producing diarrheagenic E. coli among diarrheic foals and its potential public health implications. Rectal swabs were collected from 80 diarrheic foals. These swabs were processed to isolate and identify ESBL/pAmpC-producing E. coli using a selective culture medium, biochemical tests, phenotypic identification, and molecular identification of ESBL- and pAmpC-encoding genes. Moreover, all ESBL-/pAmpC-producing E. coli isolates were examined for different virulence genes related to diarrheagenic E. coli pathotypes.

RESULTS

Out of 80 examined foals, 26 (32.5%) were confirmed as ESBL-/pAmpC-producing E. coli, of which 14 (17.5%) animals carried only ESBL-producing E. coli, whereas 12 (15%) animals possessed ESBL-pAmpC-producing E. coli. The only detected diarrheagenic pathotype was enterotoxigenic, encoded by the heat-stable enterotoxin gene (ST) with a prevalence rate of 80.8% (21/26). The ST gene was further characterized where STa, STb, and STa + STb were found in one, four, and 16 strains, respectively. Moreover, all enterotoxigenic E. coli (ETEC) isolates exhibited a multidrug-resistance pattern. The phylogenetic analysis of 3 obtained partial STb sequences revealed high genetic relatedness to ETEC isolates retrieved from humans, conferring such sequences' public health significance.

CONCLUSIONS

These findings highlight that diarrheic foals could serve as a potential reservoir for multidrug-resistant ESBL-/pAmpC-producing enterotoxigenic E. coli.

Repeat modules and N-linked glycans define structure and antigenicity of a critical enterotoxigenic E. coli adhesin

Enterotoxigenic Escherichia coli (ETEC) cause hundreds of millions of cases of infectious diarrhea annually, predominantly in children from low-middle income regions. Notably, in children, as well as volunteers challenged with ETEC, diarrheal severity is significantly increased in blood group A (bgA) individuals. EtpA, is a secreted glycoprotein adhesin that functions as a blood group A lectin to promote critical interactions between ETEC and blood group A glycans on intestinal epithelia for effective bacterial adhesion and toxin delivery. EtpA is highly immunogenic resulting in robust antibody responses following natural infection and experimental challenge of volunteers with ETEC. To understand how EtpA directs ETEC-blood group A interactions and stimulates adaptive immunity, we mutated EtpA, mapped its glycosylation by mass-spectrometry (MS), isolated polyclonal (pAbs) and monoclonal antibodies (mAbs) from vaccinated mice and ETEC-infected volunteers, and determined structures of antibody-EtpA complexes by cryo-electron microscopy. Both bgA and mAbs that inhibited EtpA-bgA interactions and ETEC adhesion, bound to the C-terminal repeat domain highlighting this region as crucial for ETEC pathogen-host interaction. MS analysis uncovered extensive and heterogeneous N-linked glycosylation of EtpA and cryo-EM structures revealed that mAbs directly engage these unique glycan containing epitopes. Finally, electron microscopy-based polyclonal epitope mapping revealed antibodies targeting numerous distinct epitopes on N and C-terminal domains, suggesting that EtpA vaccination generates responses against neutralizing and decoy regions of the molecule. Collectively, we anticipate that these data will inform our general understanding of pathogen-host glycan interactions and adaptive immunity relevant to rational vaccine subunit design.

The role of vaccines in reducing antimicrobial resistance: A review of potential impact of vaccines on AMR and insights across 16 vaccines and pathogens

In 2019, an estimated 4.95 million deaths were linked to antimicrobial resistance (AMR). Vaccines can prevent many of these deaths by averting both drug-sensitive and resistant infections, reducing antibiotic usage, and lowering the likelihood of developing resistance genes. However, their role in mitigating AMR is currently underutilized. This article builds upon previous research that utilizes Vaccine Value Profiles-tools that assess the health, socioeconomic, and societal impact of pathogens-to inform vaccine development. We analyze the effects of 16 pathogens, covered by Vaccine Value Profiles, on AMR, and explore how vaccines could reduce AMR. The article also provides insights into vaccine development and usage. Vaccines are crucial in lessening the impact of infectious diseases and curbing the development of AMR. To fully realize their potential, vaccines must be more prominently featured in the overall strategy to combat AMR. This requires ongoing investment in research and development of new vaccines and the implementation of additional prevention and control measures to address this global threat effectively.

Special Issue on Enterotoxigenic Escherichia coli (ETEC) Vaccines: ETEC Infection and Vaccine-Mediated Immunity

Enterotoxigenic Escherichia coli (ETEC) is the most prevalent bacterial pathogen causing young children to suffer acute watery diarrhea in Low- and Middle-Income Countries (LMICs) [...].

Repeat modules and N-linked glycans define structure and antigenicity of a critical enterotoxigenic E. coli adhesin

Enterotoxigenic Escherichia coli (ETEC) cause hundreds of millions of cases of infectious diarrhea annually, predominantly in children from low-middle income regions. Notably, in children, as well as human volunteers challenged with ETEC, diarrheal severity is significantly increased severity in blood group A (bgA) individuals. EtpA, is a secreted glycoprotein adhesin that functions as a blood group A lectin to promote critical interactions between ETEC and blood group A glycans on intestinal epithelia for effective bacterial adhesion and toxin delivery. EtpA is highly immunogenic resulting in robust antibody responses following natural infection and experimental challenge of human volunteers with ETEC. To understand how EtpA directs ETEC-blood group A interactions and stimulates adaptive immunity, we mutated EtpA, mapped its glycosylation by mass-spectrometry (MS), isolated polyclonal (pAbs) and monoclonal antibodies (mAbs) from vaccinated mice and ETEC-infected human volunteers, and determined structures of antibody-EtpA complexes by cryo-electron microscopy. Both bgA and mAbs that inhibited EtpA-bgA interactions and ETEC adhesion, bound to the C-terminal repeat domain highlighting this region as crucial for ETEC pathogen-host interaction. MS analysis uncovered extensive and heterogeneous N-linked glycosylation of EtpA and cryo-EM structures revealed that mAbs directly engage these unique glycan containing epitopes. Finally, electron microscopy-based polyclonal epitope mapping revealed antibodies targeting numerous distinct epitopes on N and C-terminal domains, suggesting that EtpA vaccination generates responses against neutralizing and decoy regions of the molecule. Collectively, we anticipate that these data will inform our general understanding of pathogen-host glycan interactions and adaptive immunity relevant to rational vaccine subunit design.

Colonization factors of human and animal-specific enterotoxigenic Escherichia coli (ETEC)

Colonization factors (CFs) are major virulence factors of enterotoxigenic Escherichia coli (ETEC). This pathogen is among the most common causes of bacterial diarrhea in children in low- and middle-income countries, travelers, and livestock. CFs are major candidate antigens in vaccines under development as preventive measures against ETEC infections in humans and livestock. Recent molecular studies have indicated that newly identified CFs on human ETEC are closely related to animal ETEC CFs. Increased knowledge of pathogenic mechanisms, immunogenicity, regulation, and expression of ETEC CFs, as well as the possible spread of animal ETEC to humans, may facilitate the future development of ETEC vaccines for humans and animals. Here, we present an updated review of CFs in ETEC.

The Incidence and Risk Factors for Enterotoxigenic E. coli Diarrheal Disease in Children under Three Years Old in Lusaka, Zambia

This study aimed to estimate the incidence and risk factors for Enterotoxigenic Escherichia coli (ETEC) diarrhea. This was a prospective cohort study of children recruited in a household census. Children were enrolled if they were 36 months or below. A total of 6828 children were followed up passively for 12 months to detect episodes of ETEC diarrhea. Diarrheal stool samples were tested for ETEC using colony polymerase chain reaction (cPCR). Among the 6828 eligible children enrolled, a total of 1110 presented with at least one episode of diarrhea. The overall incidence of ETEC diarrhea was estimated as 2.47 (95% confidence interval (CI): 2.10-2.92) episodes per 100 child years. Children who were HIV-positive (adjusted Hazard ratio (aHR) = 2.14, 95% CI: 1.14 to 3.99; p = 0.017) and those whose source of drinking water was public tap/borehole/well (aHR = 2.45, 95% CI: 1.48 to 4.06; p < 0.002) were at increased risk of ETEC diarrhea. This study found that children whose mothers have at least senior secondary school education (aHR = 0.49, 95% CI: 0.29 to 0.83; p = 0.008) were at decreased risk of ETEC diarrhea. Our study emphasizes the need for integrated public health strategies focusing on water supply improvement, healthcare for persons living with HIV, and maternal education.

Epidemiology of enterotoxigenic Escherichia coli and impact on the growth of children in the first two years of life in Lima, Peru

Background

Enterotoxigenic E. coli (ETEC) is a leading cause of diarrheal morbidity and mortality in children, although the data on disease burden, epidemiology, and impact on health at the community level are limited.

Methods

In a longitudinal birth cohort study of 345 children followed until 24 months of age in Lima, Peru, we measured ETEC burden in diarrheal and non-diarrheal samples using quantitative PCR (LT, STh, and STp toxin genes), studied epidemiology and measured anthropometry in children.

Results

About 70% of children suffered from one or more ETEC diarrhea episodes. Overall, the ETEC incidence rate (IR) was 73 per 100 child-years. ETEC infections began early after birth causing 10% (8.9-11.1) ETEC-attributable diarrheal burden at the population level (PAF) in neonates and most of the infections (58%) were attributed to ST-ETEC [PAF 7.9% (1.9-13.5)] and LT + ST-ETEC (29%) of which all the episodes were associated with diarrhea. ETEC infections increased with age, peaking at 17% PAF (4.6-27.7%; p = 0.026) at 21 to 24 months. ST-ETEC was the most prevalent type (IR 32.1) with frequent serial infections in a child. The common colonization factors in ETEC diarrhea cases were CFA/I, CS12, CS21, CS3, and CS6, while in asymptomatic ETEC cases were CS12, CS6 and CS21. Only few (5.7%) children had repeated infections with the same combination of ETEC toxin(s) and CFs, suggested genotype-specific immunity from each infection. For an average ETEC diarrhea episode of 5 days, reductions of 0.060 weight-for-length z-score (0.007 to 0.114; p = 0.027) and 0.061 weight-for-age z-score (0.015 to 0.108; p = 0.009) were noted in the following 30 days.

Conclusion

This study showed that ETEC is a significant pathogen in Peruvian children who experience serial infections with multiple age-specific pathotypes, resulting in transitory growth impairment.

Dextran and levan exopolysaccharides from tempeh-associated lactic acid bacteria with bioactivity against enterotoxigenic Escherichia coli (ETEC)

Soybean tempeh contains bioactive carbohydrate that can reduce the severity of diarrhea by inhibiting enterotoxigenic Escherichia coli (ETEC) adhesion to mammalian epithelial cells. Lactic acid bacteria (LAB) are known to be present abundantly in soybean tempeh. Some LAB species can produce exopolysaccharides (EPS) with anti-adhesion bioactivity against ETEC but there has been no report of anti-adhesion bioactive EPS from tempeh-associated LAB. We isolated EPS-producing LAB from tempeh-related sources, identified them, unambiguously elucidated their EPS structure and assessed the bioactivity of their EPS against ETEC. Pediococcus pentosaceus TL, Leuconostoc mesenteroides WA and L. mesenteroides WN produced both dextran (α-1,6 linked glucan; >1000 kDa) and levan (β-2,6 linked fructan; 650-760 kDa) in varying amounts and Leuconostoc citreum TR produced gel-forming α-1,6-mixed linkage dextran (829 kDa). All four isolates produced EPS that could adhere to ETEC cells and inhibit auto-aggregation of ETEC. EPS-PpTL, EPS-LmWA and EPS-LmWN were more bioactive towards pig-associated ETEC K88 while EPS-LcTR was more bioactive against human-associated ETEC H10407. Our finding is the first to report on the bioactivity of dextran against ETEC. Tempeh is a promising source of LAB isolates that can produce bioactive EPS against ETEC adhesion and aggregation.

Progress in methods for the detection of viable Escherichia coli

Escherichia coli (E. coli) is a prevalent enteric bacterium and a necessary organism to monitor for food safety and environmental purposes. Developing efficient and specific methods is critical for detecting and monitoring viable E. coli due to its high prevalence. Conventional culture methods are often laborious and time-consuming, and they offer limited capability in detecting potentially harmful viable but non-culturable E. coli in the tested sample, which highlights the need for improved approaches. Hence, there is a growing demand for accurate and sensitive methods to determine the presence of viable E. coli. This paper scrutinizes various methods for detecting viable E. coli, including culture-based methods, molecular methods that target DNAs and RNAs, bacteriophage-based methods, biosensors, and other emerging technologies. The review serves as a guide for researchers seeking additional methodological options and aiding in the development of rapid and precise assays. Moving forward, it is anticipated that methods for detecting E. coli will become more stable and robust, ultimately contributing significantly to the improvement of food safety and public health.

Epidemiology of Enterotoxigenic Escherichia coli among Children and Adults Seeking Care at Hospitals in Two Geographically Distinct Rural Areas in Bangladesh

Enterotoxigenic Escherichia coli (ETEC) infections undeniably continue to have substantial morbidity and mortality in younger children; however, limited data are available on the disease burden of older children and adults and on ETEC epidemiology by geographical location at the subnational level. Facility-based surveillance over the years was established to identify patients with ETEC diarrhea in two geographically distinct areas in rural Bangladesh, Chhatak in the north and Mathbaria in the southern coastal area. ETEC was highly prevalent in both areas, while the proportions, toxin types and colonization factors varied by location, season and age groups. Children < 5 years old and adults between 20 and 60 years old were at the highest risk of ETEC diarrhea which required urgent care. This study underscores the importance of capturing subnational and seasonal variations in ETEC epidemiology. ETEC vaccine developers and public health stakeholders may need to target adults between 20 and 60 years of age in addition to young children as new vaccines currently under development become licensed and introduction begins.

Efficacy Evaluation of an Intradermally Delivered Enterotoxigenic Escherichia coli CF Antigen I Fimbrial Tip Adhesin Vaccine Coadministered with Heat-Labile Enterotoxin with LT(R192G) against Experimental Challenge with Enterotoxigenic E. coli H10407 in Healthy Adult Volunteers

BACKGROUND

Enterotoxigenic E. coli (ETEC) is a principal cause of diarrhea in travelers, deployed military personnel, and children living in low to middle-income countries. ETEC expresses a variety of virulence factors including colonization factors (CF) that facilitate adherence to the intestinal mucosa. We assessed the protective efficacy of a tip-localized subunit of CF antigen I (CFA/I), CfaE, delivered intradermally with the mutant E. coli heat-labile enterotoxin, LTR192G, in a controlled human infection model (CHIM).

METHODS

Three cohorts of healthy adult subjects were enrolled and given three doses of 25 μg CfaE + 100 ng LTR192G vaccine intradermally at 3-week intervals. Approximately 28 days after the last vaccination, vaccinated and unvaccinated subjects were admitted as inpatients and challenged with approximately 2 × 107 cfu of CFA/I+ ETEC strain H10407 following an overnight fast. Subjects were assessed for moderate-to-severe diarrhea for 5 days post-challenge.

RESULTS

A total of 52 volunteers received all three vaccinations; 41 vaccinated and 43 unvaccinated subjects were challenged and assessed for moderate-to-severe diarrhea. Naïve attack rates varied from 45.5% to 64.7% across the cohorts yielding an overall efficacy estimate of 27.8% (95% confidence intervals: -7.5-51.6%). In addition to reducing moderate-severe diarrhea rates, the vaccine significantly reduced loose stool output and overall ETEC disease severity.

CONCLUSIONS

This is the first study to demonstrate protection against ETEC challenge after intradermal vaccination with an ETEC adhesin. Further examination of the challenge methodology is necessary to address the variability in naïve attack rate observed among the three cohorts in the present study.

Systemic inflammation, enteropathogenic E. Coli, and micronutrient insufficiencies in the first trimester as possible predictors of preterm birth in rural Bangladesh: a prospective study

BACKGROUND

An incomplete understanding of preterm birth is especially concerning for low-middle income countries, where preterm birth has poorer prognoses. While systemic proinflammatory processes are a reportedly normal component of gestation, excessive inflammation has been demonstrated as a risk factor for preterm birth. There is minimal research on the impact of excessive maternal inflammation in the first trimester on the risk of preterm birth in low-middle income countries specifically.

METHODS

Pregnant women were enrolled at the rural Bangladesh site of the National Institute of Child Health Global Network Maternal Newborn Health Registry. Serum samples were collected to measure concentrations of the inflammatory markers C-reactive protein (CRP) and Alpha-1-acid glycoprotein (AGP), and stool samples were collected and analyzed for enteropathogens. We examined associations of maternal markers in the first-trimester with preterm birth using logistic regression models. CRP and AGP were primarily modeled with a composite inflammation predictor.

RESULTS

Out of 376 singleton births analyzed, 12.5% were preterm. First trimester inflammation was observed in 58.8% of all births, and was significantly associated with increased odds of preterm birth (adjusted odds ratio [aOR] = 2.23; 95% confidence interval [CI]: 1.03, 5.16), independent of anemia. Maternal vitamin B12 insufficiency (aOR = 3.33; 95% CI: 1.29, 8.21) and maternal anemia (aOR = 2.56; 95% CI: 1.26, 5.17) were also associated with higher odds of preterm birth. Atypical enteropathogenic E. coli detection showed a significant association with elevated AGP levels and was significantly associated with preterm birth (odds ratio [OR] = 2.36; 95% CI: 1.21, 4.57), but not associated with CRP.

CONCLUSIONS

Inflammation, anemia, and vitamin B12 insufficiency in the first trimester were significantly associated with preterm birth in our cohort from rural Bangladesh. Inflammation and anemia were independent predictors of premature birth in this low-middle income setting where inflammation during gestation was widespread. Further research is needed to identify if infections such as enteropathogenic E. coli are a cause of inflammation in the first trimester, and if intervention for infection would decrease preterm birth.

Colicins and T6SS-based competition systems enhance enterotoxigenic E. coli (ETEC) competitiveness

Diarrheal diseases are still a significant problem for humankind, causing approximately half a million deaths annually. To cause diarrhea, enteric bacterial pathogens must first colonize the gut, which is a niche occupied by the normal bacterial microbiota. Therefore, the ability of pathogenic bacteria to inhibit the growth of other bacteria can facilitate the colonization process. Although enterotoxigenic Escherichia coli (ETEC) is one of the major causative agents of diarrheal diseases, little is known about the competition systems found in and used by ETEC and how they contribute to the ability of ETEC to colonize a host. Here, we collected a set of 94 fully assembled ETEC genomes by performing whole-genome sequencing and mining the NCBI RefSeq database. Using this set, we performed a comprehensive search for delivered bacterial toxins and investigated how these toxins contribute to ETEC competitiveness in vitro. We found that type VI secretion systems (T6SS) were widespread among ETEC (n = 47). In addition, several closely related ETEC strains were found to encode Colicin Ia and T6SS (n = 8). These toxins provide ETEC competitive advantages during in vitro competition against other E. coli, suggesting that the role of T6SS as well as colicins in ETEC biology has until now been underappreciated.

The Controlled Human Infection Model for Enterotoxigenic Escherichia coli

The controlled human infection model (CHIM) for enterotoxigenic Escherichia coli (ETEC) has been instrumental in defining ETEC as a causative agent of acute watery diarrhea, providing insights into disease pathogenesis and resistance to illness, and enabling preliminary efficacy evaluations for numerous products including vaccines, immunoprophylactics, and drugs. Over a dozen strains have been evaluated to date, with a spectrum of clinical signs and symptoms that appear to replicate the clinical illness seen with naturally occurring ETEC. Recent advancements in the ETEC CHIM have enhanced the characterization of clinical, immunological, and microbiological outcomes. It is anticipated that omics-based technologies applied to ETEC CHIMs will continue to broaden our understanding of host-pathogen interactions and facilitate the development of primary and secondary prevention strategies.

A Perspective on the Strategy for Advancing ETVAX®, An Anti-ETEC Diarrheal Disease Vaccine, into a Field Efficacy Trial in Gambian Children: Rationale, Challenges, Lessons Learned, and Future Directions

For the first time in over 20 years, an Enterotoxigenic Escherichia coli (ETEC) vaccine candidate, ETVAX®, has advanced into a phase 2b field efficacy trial for children 6-18 months of age in a low-income country. ETVAX® is an inactivated whole cell vaccine that has gone through a series of clinical trials to provide a rationale for the design elements of the Phase 2b trial. This trial is now underway in The Gambia and will be a precursor to an upcoming pivotal phase 3 trial. To reach this point, numerous findings were brought together to define factors such as safe and immunogenic doses for children, and the possible benefit of a mucosal adjuvant, double mutant labile toxin (dmLT). Considering the promising but still underexplored potential of inactivated whole cells in oral vaccination, we present a perspective compiling key observations from past ETVAX® trials that informed The Gambian trial design. This report will update the trial's status and explore future directions for ETEC vaccine trials. Our aim is to provide not only an update on the most advanced ETEC vaccine candidate but also to offer insights beneficial for the development of other much-needed oral whole-cell vaccines against enteric and other pathogens.

Development of a new candidate vaccine against piglet diarrhea caused by Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is an important type of pathogenic bacteria that causes diarrhea in humans and young livestock. The pathogen has a high morbidity and mortality rate, resulting in significant economic losses in the pig industry. To effectively prevent piglet diarrhea, we developed a new tetravalent genetically engineered vaccine that specifically targets ETEC. To eliminate the natural toxin activity of ST1 enterotoxin and enhance the preventive effect of the vaccine, the mutated ST 1, K88ac, K99, and LT B genes were amplified by PCR and site-specific mutation techniques. The recombinant strain BL21(DE3)(pXKK3SL) was constructed and achieved high expression. Animal experiments showed that the inactivated vaccine had eliminated the natural toxin activity of ST1. The immune protection test demonstrated that the inclusion body and inactivated vaccine exhibited a positive immune effect. The protection rates of the inclusion body group and inactivated vaccine group were 96 and 98%, respectively, when challenged with 1 minimum lethal dose, indicating that the constructed K88ac-K99-3ST1-LTB vaccine achieved a strong immune effect. Additionally, the minimum immune doses for mice and pregnant sows were determined to be 0.2 and 2 mL, respectively. This study suggests that the novel K88ac-K99-3ST1-LTB vaccine has a wide immune spectrum and can prevent diarrhea caused by ETEC through enterotoxin and fimbrial pathways. The aforementioned research demonstrates that the K88ac-K99-3ST1-LTB vaccine offers a new genetically engineered vaccine that shows potential for preventing diarrhea in newborn piglets.

Protective effect of Limosilactobacillus reuteri-fermented yogurt on mouse intestinal barrier injury induced by enterotoxigenic Escherichia coli

BACKGROUND

Enterotoxigenic Escherichia coli (ETEC) is a pathogen that causes traveler's diarrhea, for which an effective vaccine is lacking. Previous studies showed that Limosilactobacillus reuteri could inhibit E. coli, effectively increase the expression of its tight junction protein, and reduce the adhesion of ETEC to the intestinal epithelial Caco-2 cell line. In this study, three kinds of yogurt with different starter cultures were first prepared: Lm. reuteri yogurt (fermented by Lm. reuteri alone), traditional yogurt (fermented by Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus at a ratio of 1:1) and mixed yogurt (fermented by Lm. reuteri, S. thermophilus and L. delbrueckii subsp. bulgaricus at a ratio of 1:1:1). The physiological properties, oxidative stress, intestinal barrier function, tight junction protein, pathological conditions and intestinal microbiota composition were investigated.

RESULTS

The data showed that Lm. reuteri-fermented yogurt pregavage could effectively alleviate the intestinal barrier impairment caused by ETEC in mice. It alleviated intestinal villus shortening and inflammatory cell infiltration, decreased plasma diamine oxidase concentration and increased claudin-1 and occludin expression in the jejunum of ETEC-infected mice. In addition, Lm. reuteri-fermented yogurt significantly reduced the ETEC load in fecal samples, reversed the increase in Pseudomonadota abundance and decreased Bacteroidota abundance caused by ETEC infection. Furthermore, the composition of the intestinal microbiota could maintain a stable state similar to that in healthy mice.

CONCLUSION

These findings indicate that Lm. reuteri-fermented yogurt could alleviate intestinal barrier damage, inhibit ETEC growth and maintain the stability of the intestinal microbiota during ETEC infection. © 2023 Society of Chemical Industry.

Contribution of the Rapid LAMP-Based Diagnostic Test (RLDT) to the Evaluation of Enterotoxigenic Escherichia coli (ETEC) and Shigella in Childhood Diarrhea in the Peri-Urban Area of Ouagadougou, Burkina Faso

The estimates of enterotoxigenic Escherichia coli (ETEC) and Shigella burden in developing countries are limited by the lack of rapid, accessible, and sensitive diagnostics and surveillance tools. We used a "Rapid LAMP based Diagnostic Test (RLDT)" to detect ETEC and Shigella in diarrheal and non-diarrheal stool samples from a 12-month longitudinal cohort of children under five years of age in a peri-urban area of Ouagadougou in Burkina Faso (West Africa). To allow comparison with the RLDT-Shigella results, conventional culture methods were used to identify Shigella strains in the stool samples. As conventional culture alone cannot detect ETEC cases, a subset of E. coli-like colonies was tested using conventional PCR to detect ETEC toxins genes. Of the 165 stool samples analyzed for ETEC, 24.9% were positive when using RLDT against 4.2% when using culture followed by PCR. ETEC toxin distribution when using RLDT was STp 17.6% (29/165), LT 11.5% (19/165), and STh 8.5% (14/165). Of the 263 specimens tested for Shigella, 44.8% were positive when using RLDT against 23.2% when using culture. The sensitivity and specificity of the RLDT compared to culture (followed by PCR for ETEC) were 93.44% and 69.8% for Shigella and 83.7% and 77.9% for ETEC, respectively. This study indicates that both Shigella and ETEC are substantially underdiagnosed when using conventional culture and highlights the potential contribution of the new RLDT method to improve enteric disease burden estimation and to guide future efforts to prevent and control bacterial enteric infection and disease.

Safety and immunogenicity of ETVAX®, an oral inactivated vaccine against enterotoxigenic Escherichia coli diarrhoea: a double-blinded, randomized, placebo-controlled trial amongst Finnish travellers to Benin, West Africa

BACKGROUND

No licensed human vaccines are available against enterotoxigenic Escherichia coli (ETEC), a major diarrhoeal pathogen affecting children in low- and middle-income countries and foreign travellers alike. ETVAX®, a multivalent oral whole-cell vaccine containing four inactivated ETEC strains and the heat-labile enterotoxin B subunit (LTB), has proved promising in Phase 1 and Phase 1/ 2 studies.

METHODS

We conducted a Phase 2b double-blinded, randomized, placebo-controlled trial amongst Finnish travellers to Benin, West Africa. This report presents study design and safety and immunogenicity data. Volunteers aged 18-65 years were randomized 1:1 to receive ETVAX® or placebo. They visited Benin for 12 days, provided stool and blood samples and completed adverse event (AE) forms. IgA and IgG antibodies to LTB and O78 lipopolysaccharide (LPS) were measured by electrochemiluminescence.

RESULTS

The AEs did not differ significantly between vaccine (n = 374) and placebo (n = 375) recipients. Of the solicited AEs, loose stools/diarrhoea (26.7/25.9%) and stomach ache (23.0/20.0%) were reported most commonly. Of all possibly/probably vaccine-related AEs, the most frequent were gastrointestinal symptoms (54.0/48.8%) and nervous system disorders (20.3/25.1%). Serious AEs were recorded for 4.3/5.6%, all unlikely to be vaccine related. Amongst the ETVAX® recipients, LTB-specific IgA antibodies increased 22-fold. For the 370/372 vaccine/placebo recipients, the frequency of ≥2-fold increases against LTB was 81/2.4%, and against O78 LPS 69/2.7%. The majority of ETVAX® recipients (93%) responded to either LTB or O78.

CONCLUSIONS

This Phase 2b trial is the largest on ETVAX® undertaken amongst travellers to date. ETVAX® showed an excellent safety profile and proved strongly immunogenic, which encourages the further development of this vaccine.

Vaccine value profile for enterotoxigenic Escherichia coli (ETEC)

Enterotoxigenic Escherichia coli (ETEC) is one of the leading bacterial causes of diarrhoea, especially among children in low-resource settings, and travellers and military personnel from high-income countries. WHO's primary strategic goal for ETEC vaccine development is to develop a safe, effective, and affordable ETEC vaccine that reduces mortality and morbidity due to moderate-to-severe diarrhoeal disease in infants and children under 5 years of age in LMICs, as well as the long-term negative health impact on infant physical and cognitive development resulting from infection with this enteric pathogen. An effective ETEC vaccine will also likely reduce the need for antibiotic treatment and help limit the further emergence of antimicrobial resistance bacterial pathogens. The lead ETEC vaccine candidate, ETVAX, has shown field efficacy in travellers and has moved into field efficacy testing in LMIC infants and children. A Phase 3 efficacy study in LMIC infants is projected to start in 2024 and plans for a Phase 3 trial in travellers are under discussion with the U.S. FDA. Licensing for both travel and LMIC indications is projected to be feasible in the next 5-8 years. Given increasing recognition of its negative impact on child health and development in LMICs and predominance as the leading etiology of travellers' diarrhoea (TD), a standalone vaccine for ETEC is more cost-effective than vaccines targeting other TD pathogens, and a viable commercial market also exists. In contrast, combination of an ETEC vaccine with other vaccines for childhood pathogens in LMICs would maximize protection in a more cost-effective manner than a series of stand-alone vaccines. This 'Vaccine Value Profile' (VVP) for ETEC is intended to provide a high-level, holistic assessment of available data to inform the potential public health, economic and societal value of pipeline vaccines and vaccine-like products. This VVP was developed by a working group of subject matter experts from academia, non-profit organizations, public private partnerships, and multi-lateral organizations. All contributors have extensive expertise on various elements of the ETEC VVP and collectively aimed to identify current research and knowledge gaps. The VVP was developed using only existing and publicly available information.

Safety, tolerability, and immunogenicity of an oral inactivated ETEC vaccine (ETVAX®) with dmLT adjuvant in healthy adults and children in Zambia: An age descending randomised, placebo-controlled trial

BACKGROUND

Enterotoxigenic Escherichia coli (ETEC) is an important cause of moderate to severe diarrhoea in children for which there is no licensed vaccine. We evaluated ETVAX®, an oral, inactivated ETEC vaccine containing four E. coli strains over-expressing the major colonization factors CFA/I, CS3, CS5, and CS6, a toxoid (LCTBA) and double mutant heat-labile enterotoxin (dmLT) adjuvant for safety, tolerability, and immunogenicity.

METHODS

A double-blind, placebo-controlled, age-descending, dose-finding trial was undertaken in 40 adults, 60 children aged 10-23 months, and 146 aged 6-9 months. Adults received one full dose of ETVAX® and children received 3 doses of either 1/4 or 1/8 dose. Safety was evaluated as solicited and unsolicited events for 7 days following vaccination. Immunogenicity was assessed by evaluation of plasma IgA antibody responses to CFA/I, CS3, CS5, CS6, and LTB, and IgG responses to LTB.

RESULTS

Solicited adverse events were mostly mild or moderate with only 2 severe fever reports which were unrelated to the vaccine. The most common events were abdominal pain in adults (26.7 % in vaccinees vs 20 % in placebos), and fever in children aged 6-9 months (44 % vs 54  %). Dosage, number of vaccinations and decreasing age had no influence on severity or frequency of adverse events. The vaccine induced plasma IgA and IgG responses against LTB in 100 % of the adults and 80-90 % of the children. In the 6-23 months cohort, IgA responses to more than 3 vaccine antigens after 3 doses determined as ≥2-fold rise was significantly higher for 1/4 dose compared to placebo (56.7 % vs 27.2 %, p = 0.01). In the 6-9 months cohort, responses to the 1/4 dose were significantly higher than 1/8 dose after 3 rather than 2 doses.

CONCLUSION

ETVAX® was safe, tolerable, and immunogenic in Zambian adults and children. The 1/4 dose induced significantly stronger IgA responses and is recommended for evaluation of protection in children.

CLINICAL TRIALS REGISTRATION

The trial is registered with the Pan African Clinical Trials Registry (PACTR Ref. 201905764389804) and a description of this clinical trial is available on: https://pactr.samrc.ac.za/Trial Design.

Guanylate cyclase-C Signaling Axis as a theragnostic target in colorectal cancer: a systematic review of literature

Introduction

Colorectal cancer (CRC) is a devastating disease that affects millions of people worldwide. Recent research has highlighted the crucial role of the guanylate cyclase-C (GC-C) signaling axis in CRC, from the early stages of tumorigenesis to disease progression. GC-C is activated by endogenous peptides guanylin (GU) and uroguanylin (UG), which are critical in maintaining intestinal fluid homeostasis. However, it has been found that these peptides may also contribute to the development of CRC. This systematic review focuses on the latest research on the GC-C signaling axis in CRC.

Methods

According to the aim of the study, a systematic literature search was conducted on Medline and PubMed databases. Ultimately, a total of 40 articles were gathered for the systematic review.

Results

Our systematic literature search revealed that alterations in GC-C signaling compartments in CRC tissue have demonstrated potential as diagnostic, prognostic, and therapeutic markers. This research highlights a potential treatment for CRC by targeting the GC-C signaling axis. Promising results from recent studies have explored the use of this signaling axis to develop new vaccines and chimeric antigen receptors that may be used in future clinical trials.

Conclusion

The findings presented in this review provide compelling evidence that targeting the GC-C signaling axis may be an advantageous approach for treating CRC.

Mitigating the effects of climate change on human health with vaccines and vaccinations

Climate change represents an unprecedented threat to humanity and will be the ultimate challenge of the 21st century. As a public health consequence, the World Health Organization estimates an additional 250,000 deaths annually by 2030, with resource-poor countries being predominantly affected. Although climate change's direct and indirect consequences on human health are manifold and far from fully explored, a growing body of evidence demonstrates its potential to exacerbate the frequency and spread of transmissible infectious diseases. Effective, high-impact mitigation measures are critical in combating this global crisis. While vaccines and vaccination are among the most cost-effective public health interventions, they have yet to be established as a major strategy in climate change-related health effect mitigation. In this narrative review, we synthesize the available evidence on the effect of climate change on vaccine-preventable diseases. This review examines the direct effect of climate change on water-related diseases such as cholera and other enteropathogens, helminthic infections and leptospirosis. It also explores the effects of rising temperatures on vector-borne diseases like dengue, chikungunya, and malaria, as well as the impact of temperature and humidity on airborne diseases like influenza and respiratory syncytial virus infection. Recent advances in global vaccine development facilitate the use of vaccines and vaccination as a mitigation strategy in the agenda against climate change consequences. A focused evaluation of vaccine research and development, funding, and distribution related to climate change is required.

Developments in oral enterotoxigenic Escherichia coli vaccines

Enterotoxigenic Escherichia coli (ETEC) is a leading cause of diarrhea in children in developing countries and in travelers. WHO has affirmed ETEC as a priority vaccine target, but there is no licensed ETEC vaccine available yet. We here describe recent, promising developments of different live, inactivated, and subunit ETEC candidate vaccines expressing or containing nontoxic enterotoxin and/or colonization factor antigens with a focus on oral vaccines. Many of the ETEC candidate vaccines have been tested in clinical trials for safety and immunogenicity and some of them also for protective efficacy in field trials or in challenge studies.

Efficacy of an Enterotoxigenic Escherichia coli (ETEC) Vaccine on the Incidence and Severity of Traveler's Diarrhea (TD): Evaluation of Alternative Endpoints and a TD Severity Score

The efficacy of an Oral Whole Cell ETEC Vaccine (OEV) against Travelers' Diarrhea (TD) was reexamined using novel outcome and immunologic measures. More specifically, a recently developed disease severity score and alternative clinical endpoints were evaluated as part of an initial validation effort to access the efficacy of a vaccine intervention for the first time in travelers to an ETEC endemic area. A randomized, double-blind, placebo-controlled trial followed travelers to Guatemala or Mexico up to 28 days after arrival in the country following vaccination (two doses two weeks apart) with an ETEC vaccine. Fecal samples were collected upon arrival, departure, and during TD for pathogen identification. Serum was collected in a subset of subjects to determine IgA cholera toxin B subunit (CTB) antibody titers upon their arrival in the country. The ETEC vaccine's efficacy, utilizing a TD severity score and other alternative endpoints, including the relationship between antibody levels and TD risk, was assessed and compared to the per-protocol primary efficacy endpoint. A total of 1435 subjects completed 7-28 days of follow-up and had available data. Vaccine efficacy was higher against more severe (≥5 unformed stools/24 h) ETEC-attributable TD and when accounting for immunologic take (PE ≥ 50%; p < 0.05). The vaccine protected against less severe (3 and 4 unformed stools/24 h) ETEC-attributable TD when accounting for symptom severity or change in activity (PE = 76.3%, p = 0.01). Immunologic take of the vaccine was associated with a reduced risk of infection with ETEC and other enteric pathogens, and with lower TD severity. Clear efficacy was observed among vaccinees with a TD score of ≥4 or ≥5, regardless of immunologic take (PE = 72.0% and 79.0%, respectively, p ≤ 0.03). The vaccine reduced the incidence and severity of ETEC, and this warrants accelerated evaluation of the improved formulation (designated ETVAX), currently undergoing advanced field testing. Subjects with serum IgA titers to CTB had a lower risk of infection with ETEC and Campylobacter jejuni/coli. Furthermore, the TD severity score provided a more robust descriptor of disease severity and should be included as an endpoint in future studies.

Seroprevalence Study of Conserved Enterotoxigenic Escherichia coli Antigens in Globally Diverse Populations

Enterotoxigenic Escherichia coli (ETEC) are common causes of infectious diarrhea among young children of low-and middle-income countries (LMICs) and travelers to these regions. Despite their significant contributions to the morbidity and mortality associated with childhood and traveler's diarrhea, no licensed vaccines are available. Current vaccine strategies may benefit from the inclusion of additional conserved antigens, which may contribute to broader coverage and enhanced efficacy, given their key roles in facilitating intestinal colonization and effective enterotoxin delivery. EatA and EtpA are widely conserved in diverse populations of ETEC, but their immunogenicity has only been studied in controlled human infection models and a population of children in Bangladesh. Here, we compared serologic responses to EatA, EtpA and heat-labile toxin in populations from endemic regions including Haitian children and subjects residing in Egypt, Cameroon, and Peru to US children and adults where ETEC infections are sporadic. We observed elevated IgG and IgA responses in individuals from endemic regions to each of the antigens studied. In a cohort of Haitian children, we observed increased immune responses following exposure to each of the profiled antigens. These findings reflect the wide distribution of ETEC infections across multiple endemic regions and support further evaluation of EatA and EtpA as candidate ETEC vaccine antigens.

Optimization of Enterotoxigenic Escherichia coli (ETEC) Outer Membrane Vesicles Production and Isolation Method for Vaccination Purposes

The study addresses Enterotoxigenic Escherichia coli (ETEC), a significant concern in low-income countries. Despite its prevalence, there is no licensed vaccine against ETEC. Bacterial vesicle-based vaccines are promising due to their safety and diverse virulence factors. However, cost-effective production requires enhancing vesicle yield while considering altered properties due to isolation methods. The proposed method involves heat treatment and ultrafiltration to recover vesicles from bacterial cultures. Two vesicle types, collected from heat-treated (HT-OMV) or untreated (NT-OMV) cultures, were compared. Vesicles were isolated via ultrafiltration alone ("complete") or with ultracentrifugation ("sediment"). Preliminary findings suggest complete HT-OMV vesicles are suitable for an ETEC vaccine. They express important proteins (OmpA, OmpX, OmpW) and virulence factors (adhesin TibA). Sized optimally (50-200 nm) for mucosal vaccination, they activate macrophages, inducing marker expression (CD40, MHCII, CD80, CD86) and Th1/Th2 cytokine release (IL-6, MCP-1, TNF-α, IL12p70, IL-10). This study confirms non-toxicity in RAW 264.7 cells and the in vivo ability of complete HT-OMV to generate significant IgG2a/IgG1 serum antibodies. Results suggest promise for a cost-effective ETEC vaccine, requiring further research on in vivo toxicity, pathogen-specific antibody detection, and protective efficacy.

Towards a post-pandemic future for global pathogen genome sequencing

Pathogen genome sequencing has become a routine part of our response to active outbreaks of infectious disease and should be an important part of our preparations for future epidemics. In this Essay, we discuss the innovations that have enabled routine pathogen genome sequencing, as well as how genome sequences can be used to understand and control the spread of infectious disease. We also explore the impact of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) pandemic on the field of pathogen genomics and outline the challenges we must address to further improve the utility of pathogen genome sequencing in the future.

Formulation Studies to Develop Low-Cost, Orally-Delivered Secretory IgA Monoclonal Antibodies for Passive Immunization Against Enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is a common cause for diarrheal infections in children in low- and middle-income countries (LMICs). To date, no ETEC vaccine candidates have been approved. Passive immunization with low-cost, oral formulations of secretory IgA (sIgA) against ETEC is an alternative approach to protect high-risk populations in LMICs. Using a model sIgA monoclonal antibody (anti-LT sIgA2-mAb), the stability profiles of different formulations were assessed during storage and in in vitro digestion models (mimicking in vivo oral delivery). First, by employing various physicochemical techniques and a LT-antigen binding assay, three formulations with varying acid-neutralizing capacity (ANC) were evaluated to stabilize sIgA2-mAb during stress studies (freeze-thaw, agitation, elevated temperature) and during exposure to gastric phase digestion. Next, a low-volume, in vitro intestinal digestion model was developed to screen various additives to stabilize sIgA2-mAb in the intestinal phase. Finally, combinations of high ANC buffers and decoy proteins were assessed to collectively protect sIgA2-mAb during in vitro sequential (stomach to intestine) digestion. Based on the results, we demonstrate the feasibility of low-cost, 'single-vial', liquid formulations of sIgA-mAbs delivered orally after infant feeding for passive immunization, and we suggest future work based on a combination of in vitro and in vivo stability considerations.

Production of monoclonal antibody of heat-labile toxin A subunit to identify enterotoxigenic Escherichia coli by epitope mapping using synthetic peptides

Background

Enterotoxigenic Escherichia coli (ETEC) is a major cause of diarrhea through two enterotoxins, a heat-labile toxin and a heat-stable toxin. These toxins alter the cellular signaling pathways, ultimately triggering an increase in chloride secretion and watery diarrhea.

Objective

For the development of an ETEC vaccine, we attempted to construct a peptide-specific monoclonal antibody library against heat-labile enterotoxin A subunit (LT-A) by epitope mapping using synthetic peptides.

Methods

Sera produced by five mice immunized with recombinant LT-A protein were examined for specific recognition with synthetic 15-mer and 34-mer peptides of LT-A proteins using enzyme-linked immunosorbent assay. The analysis revealed that the synthetic peptides number 8, 16, 24, 33, 36, 38, and 39 reacted with an anti-LT-A polyclonal antibody. For the possible prediction of LT-A epitopes, each full-length protein sequence was subjected to BCPreds analysis and three-dimensional protein structure analysis. The data showed that three peptides (synthetic peptide numbers: 33, 36, and 38-39) have identical antigenic specificities with LT-A protein, suggesting the usefulness of these linear peptide epitopes.

Results

Based on these peptides, we produced monoclonal antibodies to improve the specificity of LT-A detection. Monoclonal antibodies produced from two peptides (numbers 33 and 36) showed affinity for an LT-A recombinant antigen. Moreover, peptide epitope prediction analysis showed that the sites of the three peptides were identical to those exhibiting actual antigenicity. Also, it was confirmed that the amino acid sequence that actually showed antigenicity was included in the peptide predicted only by ETEC-LT-A-33. Also, the specificity of the antibody for ETEC-LT-A-33 was validated using bacterial cells, and the neutralizing effect of the antibody was determined by assessing cytokine release in infected HCT-8 cells.

Conclusion

The monoclonal antibodies produced in this study are useful toolsfor vaccine production against ETEC and can be used to identify peptide antigencandidates.

Prevalence of diarrheagenic Escherichia coli and impact on child health in Cap-Haitien, Haiti

BACKGROUND

Diarrheagenic Escherichia coli (DEC) are common pathogens infecting children during their growth and development. Determining the epidemiology and the impact of DEC on child anthropometric measures informs prioritization of prevention efforts. These relationships were evaluated in a novel setting, Cap-Haitien, Haiti.

METHODS

We performed pre-specified secondary analysis of a case-control study of community-dwelling children, 6-36 months of age, enrolled 96 cases with diarrhea and 99 asymptomatic controls. Assessments were performed at enrollment and one month later at follow-up. Established endpoint PCR methodologies targeted DEC gDNA isolated from fecal swabs. The association between DEC and anthropometric z-scores at enrollment was determined using multivariate linear regression. Lastly, we assessed the association between specific biomarkers, choline and docosahexaenoic acid (DHA) and diarrheal burden.

RESULTS

Enterotoxigenic Escherichia coli (ETEC) was identified in 21.9% of cases vs. 16.1% of controls with heat-stable producing ETEC significantly associated with symptomatic disease. Enteroaggregative E. coli (EAEC) was found in 30.2% of cases vs. 27.3% of controls, and typical enteropathogenic E. coli in 6.3% vs. 4.0% of cases and controls, respectively. Multivariate linear regression, controlled for case or control status, demonstrated ETEC and EAEC were significantly associated with reduced weight-age z-score (WAZ) and height-age z-score (HAZ) after adjusting for confounders. An interaction between ETEC and EAEC was observed. Choline and DHA were not associated with diarrheal burden.

CONCLUSIONS

DEC are prevalent in north Haitian children. ETEC, EAEC, household environment, and diet are associated with unfavorable anthropometric measures, with possible synergistic interactions between ETEC and EAEC. Further studies with longer follow up may quantify the contribution of individual pathogens to adverse health outcomes.

Use of an ETEC Proteome Microarray to Evaluate Cross-Reactivity of ETVAX® Vaccine-Induced IgG Antibodies in Zambian Children

Developing a broadly protective vaccine covering most ETEC variants has been elusive. The most clinically advanced candidate yet is an oral inactivated ETEC vaccine (ETVAX^®). We report on the use of a proteome microarray for the assessment of cross-reactivity of anti-ETVAX^® IgG antibodies against over 4000 ETEC antigens and proteins. We evaluated 40 (pre-and post-vaccination) plasma samples from 20 Zambian children aged 10-23 months that participated in a phase 1 trial investigating the safety, tolerability, and immunogenicity of ETVAX^® adjuvanted with dmLT. Pre-vaccination samples revealed high IgG responses to a variety of ETEC proteins including classical ETEC antigens (CFs and LT) and non-classical antigens. Post-vaccination reactivity to CFA/I, CS3, CS6, and LTB was stronger than baseline among the vaccinated compared to the placebo group. Interestingly, we noted significantly high post-vaccination responses to three non-vaccine ETEC proteins: CS4, CS14, and PCF071 (p = 0.043, p = 0.028, and p = 0.00039, respectively), suggestive of cross-reactive responses to CFA/I. However, similar responses were observed in the placebo group, indicating the need for larger studies. We conclude that the ETEC microarray is a useful tool for investigating antibody responses to numerous antigens, especially because it may not be practicable to include all antigens in a single vaccine.

Oral inactivated whole cell vaccine for mucosal immunization: ETVAX case study

Oral immunization is an effective strategy for inducing protective immunity against mucosal enteric pathogens. Although live-attenuated as well as subunit approaches have been explored for vaccination against enteric pathogens, inactivated whole bacterial cells may also be effective in introducing protective immunity. Successfully accomplishing this goal with inactivated whole bacterial cells will require that a complex antigenic repertoire be presented in controlled immunogenic amounts, in a safe and relatively simple and self-contained delivery format. The benefit from immunization with whole cell vaccines can be further enhanced through genetic engineering to over-express selected antigens and also by the use of mucosal adjuvants to direct a more robust immunologic response. These steps are being taken for the development of ETVAX, the most clinically advanced vaccine candidate against the major enteric pathogen, enterotoxigenic Escherichia coli (ETEC) with significant positive impact.

The Diversity of Escherichia coli Pathotypes and Vaccination Strategies against This Versatile Bacterial Pathogen

Escherichia coli (E. coli) is a gram-negative bacillus and resident of the normal intestinal microbiota. However, some E. coli strains can cause diseases in humans, other mammals and birds ranging from intestinal infections, for example, diarrhea and dysentery, to extraintestinal infections, such as urinary tract infections, respiratory tract infections, meningitis, and sepsis. In terms of morbidity and mortality, pathogenic E. coli has a great impact on public health, with an economic cost of several billion dollars annually worldwide. Antibiotics are not usually used as first-line treatment for diarrheal illness caused by E. coli and in the case of bloody diarrhea, antibiotics are avoided due to the increased risk of hemolytic uremic syndrome. On the other hand, extraintestinal infections are treated with various antibiotics depending on the site of infection and susceptibility testing. Several alarming papers concerning the rising antibiotic resistance rates in E. coli strains have been published. The silent pandemic of multidrug-resistant bacteria including pathogenic E. coli that have become more difficult to treat favored prophylactic approaches such as E. coli vaccines. This review provides an overview of the pathogenesis of different pathotypes of E. coli, the virulence factors involved and updates on the major aspects of vaccine development against different E. coli pathotypes.

A Low-Cost, Thermostable, Cell-Free Protein Synthesis Platform for On-Demand Production of Conjugate Vaccines

Cell-free protein synthesis systems that can be lyophilized for long-term, non-refrigerated storage and transportation have the potential to enable decentralized biomanufacturing. However, increased thermostability and decreased reaction cost are necessary for further technology adoption. Here, we identify maltodextrin as an additive to cell-free reactions that can act as both a lyoprotectant to increase thermostability and a low-cost energy substrate. As a model, we apply optimized formulations to produce conjugate vaccines for ∼$0.50 per dose after storage at room temperature (∼22 °C) or 37 °C for up to 4 weeks, and ∼$1.00 per dose after storage at 50 °C for up to 4 weeks, with costs based on raw materials purchased at the laboratory scale. We show that these conjugate vaccines generate bactericidal antibodies against enterotoxigenic Escherichia coli (ETEC) O78 O-polysaccharide, a pathogen responsible for diarrheal disease, in immunized mice. We anticipate that our low-cost, thermostable cell-free glycoprotein synthesis system will enable new models of medicine biosynthesis and distribution that bypass cold-chain requirements.