Colonization factors among enterotoxigenic Escherichia coli isolates from children with moderate-to-severe diarrhea and from matched controls in the Global Enteric Multicenter Study (GEMS)

Role of cellular effectors in the induction and maintenance of IgA responses leading to protective immunity against enteric bacterial pathogens

The mucosal immune system is a critical first line of defense to infectious diseases, as many pathogens enter the body through mucosal surfaces, disrupting the balanced interactions between mucosal cells, secretory molecules, and microbiota in this challenging microenvironment. The mucosal immune system comprises of a complex and integrated network that includes the gut-associated lymphoid tissues (GALT). One of its primary responses to microbes is the secretion of IgA, whose role in the mucosa is vital for preventing pathogen colonization, invasion and spread. The mechanisms involved in these key responses include neutralization of pathogens, immune exclusion, immune modulation, and cross-protection. The generation and maintenance of high affinity IgA responses require a delicate balance of multiple components, including B and T cell interactions, innate cells, the cytokine milieu (e.g., IL-21, IL-10, TGF-β), and other factors essential for intestinal homeostasis, including the gut microbiota. In this review, we will discuss the main cellular components (e.g., T cells, innate lymphoid cells, dendritic cells) in the gut microenvironment as mediators of important effector responses and as critical players in supporting B cells in eliciting and maintaining IgA production, particularly in the context of enteric infections and vaccination in humans. Understanding the mechanisms of humoral and cellular components in protection could guide and accelerate the development of more effective mucosal vaccines and therapeutic interventions to efficiently combat mucosal infections.

Single domain antibodies from camelids in the treatment of microbial infections

Infectious diseases continue to pose significant global health challenges. In addition to the enduring burdens of ailments like malaria and HIV, the emergence of nosocomial outbreaks driven by antibiotic-resistant pathogens underscores the ongoing threats. Furthermore, recent infectious disease crises, exemplified by the Ebola and SARS-CoV-2 outbreaks, have intensified the pursuit of more effective and efficient diagnostic and therapeutic solutions. Among the promising options, antibodies have garnered significant attention due to their favorable structural characteristics and versatile applications. Notably, nanobodies (Nbs), the smallest functional single-domain antibodies of heavy-chain only antibodies produced by camelids, exhibit remarkable capabilities in stable antigen binding. They offer unique advantages such as ease of expression and modification and enhanced stability, as well as improved hydrophilicity compared to conventional antibody fragments (antigen-binding fragments (Fab) or single-chain variable fragments (scFv)) that can aggregate due to their low solubility. Nanobodies directly target antigen epitopes or can be engineered into multivalent Nbs and Nb-fusion proteins, expanding their therapeutic potential. This review is dedicated to charting the progress in Nb research, particularly those derived from camelids, and highlighting their diverse applications in treating infectious diseases, spanning both human and animal contexts.

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.

MecVax supplemented with CFA MEFA-II induces functional antibodies against 12 adhesins (CFA/I, CS1-CS7, CS12, CS14, CS17, and CS21) and 2 toxins (STa, LT) of enterotoxigenic Escherichia coli (ETEC)

Enterotoxigenic Escherichia coli (ETEC) strains that produce various adhesins and one or two enterotoxins are the leading causes of children's diarrhea and travelers' diarrhea. MecVax, a multivalent ETEC vaccine candidate, consists of two proteins, an adhesin multiepitope fusion antigen (MEFA) that stimulates antibodies to the seven most important ETEC adhesins (CFA/I and CS1-CS6) and a toxoid fusion antigen which stimulates antibodies against ETEC enterotoxins (heat-labile toxin and heat-stable toxin). CFA MEFA-II, another polyvalent MEFA protein, has been demonstrated to stimulate antibodies to another five important ETEC adhesins (CS7, CS12, CS14, CS17, and CS21). We hypothesize that MecVax coverage and efficacy can be expanded if MecVax could stimulate antibodies to all 12 adhesins. In this study, we supplemented MecVax with CFA MEFA-II, examined broad immunity to the 12 targeted ETEC adhesins and 2 ETEC toxins (STa, LT) in mice, and assessed mouse antibody functions for inhibiting the adherence of the 12 adhesins and neutralizing the enterotoxicity of 2 toxins, thus assessing the potential application of a broadly protective pan-ETEC vaccine. Mice intramuscularly immunized with MecVax and CFA MEFA-II developed robust antibody responses to the 12 ETEC adhesins and 2 toxins; furthermore, mouse serum antibodies showed functional activities against the adherence from each of the targeted adhesins and the enterotoxicity of either toxin. Data also indicated that CFA MEFA-II was antigenically compatible with MecVax. These results demonstrated that the inclusion of CFA MEFA-II further expands MecVax broad immunogenicity and protection coverage, suggesting the feasibility of developing a vaccine against all important diarrheal ETEC strains.IMPORTANCEThere are no vaccines licensed for Enterotoxigenic Escherichia coli (ETEC), a leading cause of children's diarrhea and the most common cause of travelers' diarrhea. Since ETEC strains produce over 25 adhesins and 2 distinctive enterotoxins, heterogeneity is a key obstacle to vaccine development. MecVax, a multivalent ETEC vaccine candidate, induces protective antibodies against the seven most important adhesins (CFA/I and CS1-CS6) associated with two-thirds of ETEC clinical cases. However, ETEC prevalence shifts chronically and geographically, and other adhesins are also associated with clinical cases. MecVax would become a pan-ETEC vaccine if it also protects against the remaining important adhesins. This study demonstrated that MecVax supplemented with adhesin protein CFA MEFA-II induces functional antibodies against 12 important ETEC adhesins (CFA/I, CS1-CS7, CS12, CS14, CS17, and CS21), enabling the development of a more broadly protective ETEC vaccine and further validating the application of the MEFA vaccinology platform for multivalent vaccine development.

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.

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.

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.

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.

Protein-based vaccine candidate MecVax broadly protects against enterotoxigenic Escherichia coli intestinal colonization in a rabbit model

There are no vaccines licensed against enterotoxigenic Escherichia coli (ETEC), a leading cause of children's diarrhea and the most common cause of travelers' diarrhea. Multivalent vaccine candidate MecVax unprecedentedly targets two ETEC enterotoxins (heat-stable toxin, STa; heat-labile toxin, LT) and the seven most prevalent ETEC adhesins (colonization factor antigen, CFA/I, coli surface antigens, CS1-CS6) and has been demonstrated preclinically to protect against STa- and LT-mediated ETEC clinical diarrhea and prevent intestinal colonization from ETEC strain H10407 (CFA/I, STa, LT). However, it is unattested whether MecVax broadly protects against intestinal colonization from ETEC strains producing the other six adhesins (CS1-CS6) also targeted by this product. In this study, we immunized rabbits with MecVax and challenged them with heterogeneous ETEC strains that express CS1-CS6 adhesins to evaluate MecVax's efficacy against bacterial intestinal colonization, thus providing broad vaccine protection against ETEC infection. Data revealed that rabbits intramuscularly immunized with MecVax developed robust responses to both ETEC enterotoxins (STa, LT) and seven adhesins (CFA/I, CS1-CS6), and when challenged with ETEC isolates expressing CS1/CS3, CS2/CS3, CS4/CS6, CS5/CS6, or CS6 adhesin, the immunized rabbits prevented over two logs (>99%) of bacteria from colonization in small intestines. Additionally, compared to a CFA-toxoid fusion protein, which is another potential ETEC vaccine antigen to target two ETEC enterotoxins and the seven adhesins, MecVax exhibited better protection against ETEC intestinal colonization. These results, in conjunction with the protection data from early studies, evidenced that MecVax is broadly protective, validating MecVax's candidacy as an effective vaccine against ETEC-associated diarrhea and accelerating ETEC vaccine development.

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.

Circulation of enterotoxigenic Escherichia coli (ETEC) isolates expressing CS23 from the environment to clinical settings

IMPORTANCE

The importance of clean water cannot be overstated. It is a vital resource for maintaining health and well-being. Unfortunately, water sources contaminated with fecal discharges from animal and human origin due to a lack of wastewater management pose a significant risk to communities, as they can become a means of transmission of pathogenic bacteria like enterotoxigenic E. coli (ETEC). ETEC is frequently found in polluted water in countries with a high prevalence of diarrheal diseases, such as Bolivia. This study provides novel insights into the circulation of ETEC between diarrheal cases and polluted water sources in areas with high rates of diarrheal disease. These findings highlight the Choqueyapu River as a potential reservoir for emerging pathogens carrying antibiotic-resistance genes, making it a crucial area for monitoring and intervention. Furthermore, the results demonstrate the feasibility of a low-cost, high-throughput method for tracking bacterial pathogens in low- and middle-income countries, making it a valuable tool for One Health monitoring efforts.

The role of the minor colonization factor CS14 in adherence to intestinal cell models by geographically diverse ETEC isolates

Enterotoxigenic Escherichia coli (ETEC) is a primary causative agent of diarrhea in travelers and young children in low- to middle-income countries. ETEC adheres to small intestinal epithelia via colonization factors (CFs) and secretes heat-stable toxin and/or heat-labile toxin, causing dysregulated ion transport and water secretion. There are over 30 CFs identified, including major CFs associated with moderate-to-severe diarrhea (MSD) and minor CFs for which a role in pathogenesis is less clear. The Global Enteric Multicenter Study identified CS14, a class 5a fimbriae, as the only minor CF significantly associated with MSD and was recommended for inclusion in ETEC vaccines. Despite detection of CS14 in ETEC isolates, the sequence conservation of the CS14 operon, its role in adherence, and functional cross-reactivity to other class 5a fimbriae like CFA/I and CS4 are not understood. Sequence analysis determined that the CS14 operon is >99.9% identical among seven geographically diverse isolates with expanded sequence analysis demonstrating SNPs exclusively in the gene encoding the tip adhesin CsuD. Western blots and electron microscopy demonstrated that CS14 expression required the growth of isolates on CFA agar with the iron chelator deferoxamine mesylate. CS14 expression resulted in significantly increased adherence to cultured intestinal cells and human enteroids. Anti-CS14 antibodies and anti-CS4 antibodies, but not anti-CFA/I antibodies, inhibited the adherence of a subset of ETEC isolates, demonstrating CS14-specific inhibition with partial cross-reactivity within the class 5a fimbrial family. These data provide support for CS14 as an important fimbrial CF and its consideration as a vaccine antigen in future strategies. IMPORTANCE Enterotoxigenic Escherichia coli (ETEC) infection causes profuse watery diarrhea in adults and children in low- to middle-income countries and is a leading cause of traveler's diarrhea. Despite increased use of rehydration therapies, young children especially can suffer long-term effects including gastrointestinal dysfunction as well as stunting and malnutrition. As there is no licensed vaccine for ETEC, there remains a need to identify and understand specific antigens for inclusion in vaccine strategies. This study investigated one adhesin named CS14. This adhesin is expressed on the bacterial surface of ETEC isolates and was recently recognized for its significant association with diarrheal disease. We demonstrated that CS14 plays a role in bacterial adhesion to human target cells, a critical first step in the disease process, and that adherence could be blocked by CS14-specific antibodies. This work will significantly impact the ETEC field by supporting inclusion of CS14 as an antigen for ETEC vaccines.

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.

A Polyvalent Adhesin-Toxoid Multiepitope-Fusion-Antigen-Induced Functional Antibodies against Five Enterotoxigenic Escherichia coli Adhesins (CS7, CS12, CS14, CS17, and CS21) but Not Enterotoxins (LT and STa)

The increasing prevalence and association with moderate-to-severe diarrhea make enterotoxigenic Escherichia coli (ETEC) adhesins CS7, CS12, CS14, CS17, and CS21 potential targets of ETEC vaccines. Currently, there are no vaccines licensed to protect against ETEC, a top cause of children's diarrhea and travelers' diarrhea. Recently, a polyvalent adhesin protein (adhesin MEFA-II) was demonstrated to induce antibodies that inhibited adherence from these five ETEC adhesins and reduced the enterotoxicity of ETEC heat-stable toxin (STa), which plays a key role in causing ETEC-associated diarrhea. To improve adhesin MEFA-II for functional antibodies against STa toxin and the other ETEC toxin, heat-labile toxin (LT), we modified adhesin MEFA-II by adding another STa toxoid and an LT epitope; we examined the new antigen immunogenicity (to five adhesins and two toxins) and more importantly antibody functions against ETEC adherence and STa and LT enterotoxicity. Data show that mice intramuscularly immunized with the new antigen (adhesin MEFA-IIb) developed robust IgG responses to the targeted adhesins (CS7, CS12, CS14, CS17, and CS21) and toxins (STa and LT). Mouse antibodies inhibited the adherence of ETEC strains expressing any of these five adhesins but failed to neutralize STa or LT enterotoxicity. In further studies, rabbits intramuscularly immunized with adhesin MEFA-IIb developed robust antigen-specific antibodies; when challenged with an ETEC isolate expressing CS21 adhesin (JF2101, CS21, and STa), the immunized rabbits showed a significant reduction in intestinal colonization by ETEC bacteria. These data indicate that adhesin MEFA-IIb is broadly immunogenic and induces functional antibodies against the targeted ETEC adhesins but not the toxins.

T helper cell responses in adult diarrheal patients following natural infection with enterotoxigenic Escherichia coli are primarily of the Th17 type

Background

Infection with enterotoxigenic Escherichia coli (ETEC) gives rise to IgA antibodies against both the heat labile toxin (LT) and colonization factors (CFs), which are considered to synergistically protect against ETEC diarrhea. Since the development of ETEC-specific long lived plasma cells and memory B cells is likely to be dependent on T helper (Th) cells, we investigated if natural ETEC diarrhea elicits ETEC-specific Th cells and their relation to IgA responses.

Methods

Th cell subsets were analyzed in adult Bangladeshi patients hospitalized due to ETEC diarrhea by flow cytometric analysis of peripheral blood mononuclear cells (PBMCs) isolated from blood collected day 2, 7, 30 and 90 after hospitalization as well as in healthy controls. The LT- and CF-specific Th responses were determined by analysis of IL-17A and IFN-γ in antigen stimulated PBMC cultures using ELISA. ETEC-specific IgA secreted by circulating antibody secreting cells (plasmablasts) were analyzed by using the antibodies in lymphocyte supernatants (ALS) ELISA-based method and plasma IgA was also measured by ELISA.

Results

ETEC patients mounted significant ALS and plasma IgA responses against LTB and CFs on day 7 after hospitalization. ETEC patients had significantly elevated proportions of memory Th cells with a Th17 phenotype (CCR6+CXCR3-) in blood compared to controls, while frequencies of Th1 (CCR6-CXCR3+) or Th2 (CCR6-CXCR3-) cells were not increased. Antigen stimulation of PBMCs revealed IL-17A responses to LT, most clearly observed after stimulation with double mutant heat labile toxin (dmLT), but also with LT B subunit (LTB), and to CS6 in samples from patients with LT+ or CS6+ ETEC bacteria. Some individuals also mounted IFN-γ responses to dmLT and LTB. Levels of LTB specific IgA antibodies in ALS, but not plasma samples correlated with both IL-17A (r=0.5, p=0.02) and IFN-γ (r=0.6, p=0.01) responses to dmLT.

Conclusions

Our results show that ETEC diarrhea induces T cell responses, which are predominantly of the Th17 type. The correlations between IL-17A and IFN-g and intestine-derived plasmablast responses support that Th responses may contribute to the development of protective IgA responses against ETEC infection. These observations provide important insights into T cell responses that need to be considered in the evaluation of advanced ETEC vaccine candidates.

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.

Polyvalent Protein Adhesin MEFA-II Induces Functional Antibodies against Enterotoxigenic Escherichia coli (ETEC) Adhesins CS7, CS12, CS14, CS17, and CS21 and Heat-Stable Toxin (STa)

There are no licensed vaccines for enterotoxigenic Escherichia coli (ETEC), a common cause of children's diarrhea and travelers' diarrhea. ETEC strains producing enterotoxins (heat-labile toxin, LT; heat-stable toxin, STa) and adhesins CFA/I, CFA/II (CS1-CS3) or CFA/IV (CS4-CS6) attributed to a majority of ETEC-associated diarrheal cases, thus the two toxins (STa, LT) and the seven adhesins (CFA/I, CS1 to CS6) are historically the primary targets in ETEC vaccine development. Recent studies, however, revealed that ETEC strains with adhesins CS14, CS21, CS7, CS17, and CS12 are also prevalent and cause moderate-to-severe diarrhea; these adhesins are now considered antigen targets as well for ETEC vaccines. In this study, we applied the epitope- and structure-based multiepitope-fusion-antigen (MEFA) vaccinology platform and constructed a polyvalent protein to present immuno-dominant continuous B-cell epitopes of these five adhesins (also an STa toxoid); we then characterized this protein antigen's (termed as adhesin MEFA-II) broad immunogenicity and evaluated antibody functions against each targeted adhesin and STa toxin. Data showed that mice intramuscularly immunized with adhesin MEFA-II protein developed robust IgG to the targeted adhesins and toxin STa. Importantly, the antigen-derived antibodies significantly inhibited adherence of ETEC bacteria expressing adhesin CS7, CS12, CS14, CS17, or CS21 and reduced STa enterotoxicity. These results indicated that adhesin MEFA-II protein is broadly immunogenic and induces cross-functional antibodies, suggesting adhesin MEFA-II can be an effective ETEC vaccine antigen; if included in an ETEC vaccine candidate, adhesin MEFA-II can expand vaccine coverage and increase efficacy against ETEC-associated children's diarrhea and travelers' diarrhea. IMPORTANCE An effective vaccine is lacking against ETEC, a primary cause of children's diarrhea and traveler's diarrhea and a threat to global health. The key challenge in ETEC vaccine development is that ETEC bacteria express heterogeneous virulence determinants (>25 adhesins and two toxins). While the current strategy to target the seven most prevalent ETEC adhesins (CFA/I, CS1 to CS6) potentially lead to a vaccine against many clinical cases, the prevalence of ETEC strains shifts chronically and geographically, and ETEC expressing other adhesins, mainly CS7, CS12, CS14, CS17, and CS21, also cause moderate-to-severe diarrhea. However, it is impossible to develop an ETEC vaccine to target as many as 12 adhesins under conventional approaches. This study used a unique vaccinology platform to create a polyvalent antigen and demonstrated the antigen's broad immunogenicity and functions against the targeted ETEC adhesins, enabling the development of a broadly protective vaccine essentially against all of the important ETEC strains.

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.

Colonizing and Virulence Factors in Enterotoxigenic Escherichia coli from Peru

Enterotoxigenic Escherichia coli (ETEC) ranks among the most relevant diarrheagenic pathogens. Efforts to design vaccines to fight ETEC have been focused on colonizing factors (CFs) and atypical virulence factors (AVF). An effective vaccine must account for differences in the regional prevalence of these CFs and AVFs to be truly effective in a given area. In the present study, the presence of 16 CFs and 9 AVFs, as well as the heat-stable (ST) variants (STh or STp), was established by polymerase chain reaction in 205 Peruvian ETEC isolates (120 from diarrhea cases and 85 from healthy controls). Ninety-nine (48.3%) isolates were heat-labile, 63 (30.7%) ST, and 43 (21.0%) presented both toxins. Of ST isolates, 59 (28.8%) possessed STh, 30 (14.6%) STp, five (2.4%) both STh and STp, and 12 (5.8%) were not amplified for any variant tested. The presence of CFs was associated with diarrhea (P < 0.0001). The presence of eatA as well as concomitant presence of CSI, CS3, and CS21 and of C5 and C6 was statistically related to diarrhea cases. The present results suggests that, if effective, a vaccine considering CS6, CS20, and CS21, together with EtpA, would provide protection against 64.4% of the isolates analyzed, whereas the addition of CS12 and EAST1 would lead to 83.9% coverage. Large studies are needed to establish both the ideal candidates to be considered to develop a vaccine effective in the area, and continuous surveillance is needed to detect displacement of circulating isolates that may compromise future vaccines.

The indelible toll of enteric pathogens: Prevalence, clinical characterization, and seasonal trends in patients with acute community-acquired diarrhea in disenfranchised communities

BACKGROUND

There is little information on the epidemiology of enteric pathogens in Lebanon, a low- and middle-income country that suffers from a myriad of public health challenges. To address this knowledge gap, we aimed to assess the prevalence of enteric pathogens, identify risk factors and seasonal variations, and describe associations between pathogens among diarrheic patients in the Lebanese community.

METHODOLOGY AND PRINCIPAL FINDINGS

A multicenter cross-sectional community-based study was conducted in the north of Lebanon. Stool samples were collected from 360 outpatients suffering from acute diarrhea. Based on fecal examination using the BioFire® FilmArray® Gastrointestinal Panel assay, the overall prevalence of enteric infections was 86.1%. Enteroaggregative Escherichia coli (EAEC) was the most frequently identified (41.7%), followed by enteropathogenic E. coli (EPEC) (40.8%) and rotavirus A (27.5%). Notably, two cases of Vibrio cholerae were identified, while Cryptosporidium spp. (6.9%) was the most common parasitic agent. Overall, 27.7% (86/310) of the cases were single infections, and the majority, 73.3% (224/310), were mixed infections. Multivariable logistic regression models showed that enterotoxigenic E. coli (ETEC) and rotavirus A infections were significantly more likely to occur in the fall and winter compared to the summer. Rotavirus A infections significantly decreased with age but increased in patients living in rural areas or suffering from vomiting. We identified strong associations in the co-occurrence of EAEC, EPEC, and ETEC infections and a higher percentage of rotavirus A and norovirus GI/GII infections among EAEC-positive cases.

CONCLUSIONS

Several of the enteric pathogens reported in this study are not routinely tested in Lebanese clinical laboratories. However, anecdotal evidence suggests that diarrheal diseases are on the rise due to widespread pollution and the deterioration of the economy. Therefore, this study is of paramount importance to identify circulating etiologic agents and prioritize dwindling resources to control them and limit outbreaks in the future.

Structural and functional characterization of colonization factors AIBI-CS6 and AIIBII-CS6 of enterotoxigenic Escherichia coli

Over time, the structure and function of the broadly dispersed colonization factor (CF) CS6 of enterotoxigenic Escherichia coli (ETEC) have become more significant. CS6 is composed of tightly-associated subunits, CssA and CssB which due to presence of natural point mutation gave rise to CS6 subtypes. In contrast to the other ETEC CFs, CS6 is an afimbrial, spherical-shaped oligomers of (CssA-CssB)_n complex where 'n' is concentration dependent. In this study, we have compared AIBI-CS6 and AIIBII-CS6 structurally and functionally. The M_w of CssAI was 18.5 kDa but M_w of CssAII was 15.1 kDa. Both CssBI and CssBII had M_w of 15.9 kDa. The substitution of Gly³⁹ with Ala³⁹ in CssAI leads to reduction in Mw from 18.5 to 15.1 kDa. Due to higher M_w of CssAI, the size of AIBI concentration-dependent oligomers should be higher. However, the M_w of AIIBII oligomers were higher and AIIBII also showed higher oligomeric forms compared to AIBI both in native PAGE and electron microscopy. The oligomers of both subtypes could withstand greater temperatures and denaturant concentrations. In terms of cellular response, the levels of inflammatory cytokines were significantly higher in case of AIBI-CS6 expressing ETEC as compared to AIIBII-CS6 expressing ETEC both in vitro and in vivo. When inflammatory cytokines were evaluated after infecting suckling mice with these ETEC strains, the results were consistent. In conclusion, even though there was subtle structural difference between AIBI-CS6 and AIIBII-CS6 due to natural point mutations but ETEC strains expressing these subtypes displayed great variability in pathogenicity.

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.

Strong Association between Diarrhea and Concentration of Enterotoxigenic Escherichia coli Strain TW10722 in Stools of Experimentally Infected Volunteers

Enterotoxigenic Escherichia coli (ETEC) strains are a major cause of diarrheal illness in children and travelers in low- and middle-income countries. When volunteers are infected with ETEC strains, as part of experimental infection studies, some do not develop diarrhea. To improve our understanding of how these volunteers are protected, we investigated the association between stool ETEC DNA concentration, as determined by quantitative PCR, and the development and severity of disease in 21 volunteers who had been experimentally infected with ETEC strain TW10722. We found a strong association between maximum stool ETEC DNA concentration and the development of diarrhea: all of the 11 volunteers who did not develop diarrhea had <0.99% TW10722-specific DNA in their stools throughout the follow-up period of up to 9 days, while all of the 10 volunteers who did develop diarrhea had maximum DNA concentrations of ≥0.99%. Most likely, these maximum stool TW10722 DNA concentrations reflect the level of intestinal colonization and the risk of experiencing diarrhea, thereby, seems to be directly dependent on the level of colonization. Thus, the development and availability of vaccines and other prophylactic measures, even if they only partially reduce colonization, could be important in the effort to reduce the burden of ETEC diarrhea.

A snap-shot of a diarrheal epidemic in Dhaka due to enterotoxigenic Escherichia coli and Vibrio cholerae O1 in 2022

Background

Enterotoxigenic Escherichia coli (ETEC) and Vibrio cholerae O1 are most common bacterial causes of diarrheal diseases in Bangladesh. This analysis projected distribution of ETEC and V. cholerae O1 among diarrheal patients of icddr,b, Dhaka hospital in two diarrheal peaks of 2022.

Methodology

Under the 2% systematic surveillance system, stool samples collected from diarrheal patients of icddr,b hospital were cultured and diagnostic testing was done for ETEC and V. cholerae O1. Comparison of positive cases was done between first peak (March-April) and second peak (October-November) in 2022.

Results

A total of 2,937 stool specimens were tested of which 12% were ETEC and 20% were V. cholerae O1. About 40% of the severe dehydration cases were infected with V. cholerae O1. Predominant ETEC enterotoxin type was 'LT/ST' (41%). The LT enterotoxin significantly increased from 13% to 28% in the second peak (p = 0.015). The predominant colonization factors (CFs) on ETEC were CS5 + CS6 (23%), followed by CS6 (15%). CF-positive isolates was significantly higher in the second peak (36%) than in the first peak (22%) (p = 0.043). Total 14% cases were co-infected with ETEC and V. cholerae O1. Significant differences in the distribution of enterotoxin types were observed (p = 0.029) among the co-infection cases.

Conclusion

Changing patterns of enterotoxin and CFs observed in ETEC pathogens should be taken into consideration for ETEC vaccine development. Considering cholera and ETEC biannual trends in causing diarrheal epidemics and outbreaks, emphasizes the need for thoughts on combination vaccine strategies for preventing acute watery diarrhea due to the two major bacterial pathogens.

Plant-derived nanoparticles as alternative therapy against Diarrheal pathogens in the era of antimicrobial resistance: A review

Diarrhea is a condition in which feces is discharged from the bowels frequently and in a liquid form. It is one of the frequent causes of morbidity and mortality in developing countries. The impact of Diarrhea is worsened by the increasing incidence of antimicrobial resistance among the causative agents, and this is now categorized as a global healthcare challenge. Antimicrobial resistance among Diarrheal pathogens also contributes to extended infection durations, and huge economic loss even in countries with advanced public health policies. The ever-increasing incidence of antimicrobial resistance including the contraindications arising from the administration of antibiotics in some Diarrheal cases highlights a crucial need for the development of novel non-antibiotic alternative agents for therapeutic and biocontrol applications. One such intervention includes the application of plant-derived nanoparticles (PDNPs) with novel antimicrobial properties. Given their small size and large surface area to volume ratio, PDNPs can attack target bacterial cell walls to generate reactive oxygen species that may simultaneously disrupt bacteria cell components such as DNA and proteins leading to cell damage or death. This potential can make it very difficult for pathogenic organisms to develop resistance against these antibacterial agents. In this review, we provide a critical overview on the antimicrobial resistance crisis among Diarrheagenic bacteria. We also discuss the evidence from the existing literature to support the potential associated with the use of PDNPs as alternative therapeutic agents for multidrug resistant and antibiotics administer contraindicated bacteria that are associated with Diarrhea.

Intramuscularly Administered Enterotoxigenic Escherichia coli (ETEC) Vaccine Candidate MecVax Prevented H10407 Intestinal Colonization in an Adult Rabbit Colonization Model

Currently, there are no vaccines licensed for enterotoxigenic Escherichia coli (ETEC), a leading cause of children's diarrhea in developing countries and the most common cause of travelers' diarrhea. A vaccine preventing ETEC bacteria from colonization at small intestines and neutralizing enterotoxin toxicity is expected to be effective against ETEC diarrhea. Protein-based multivalent vaccine candidate MecVax was demonstrated recently to induce antibodies neutralizing heat-labile toxin (LT) and heat-stable toxin (STa) enterotoxicity and inhibiting adherence of seven ETEC adhesins (CFA/I, CS1 to CS6) but also to protect against ETEC toxin-mediated clinical diarrhea in a pig challenge model. To further evaluate MecVax preclinical efficacy against ETEC colonization at small intestines, in this study, we intramuscularly immunized adult rabbits with MecVax, challenged rabbits with ETEC strain H10407 (CFA/I, LT, STa), and examined prevention of bacteria intestinal colonization. Data showed that rabbits immunized with MecVax developed antibodies to both ETEC toxins (LT, STa) and seven adhesins (CFA/I, CS1 to CS6) and had over 99.9% reduction of H10407 intestinal colonization, indicating that the broadly immunogenic ETEC vaccine candidate MecVax is protective against ETEC H10407 intestinal colonization. This study also confirmed that parenteral administration of a protein-based vaccine can prevent bacteria intestinal colonization. Protection against ETEC intestinal colonization demonstrated by this rabbit study, in conjugation with protection against ETEC enterotoxin-mediated clinical diarrhea from a previous pig challenge study, suggested that MecVax can potentially be an effective ETEC vaccine and a combined pig and rabbit challenge model can evaluate ETEC vaccine preclinical efficacy. IMPORTANCE An effective ETEC vaccine would prevent hundreds of millions of diarrhea clinical cases and save nearly 100,000 lives annually. MecVax, a protein-based injectable multivalent ETEC vaccine candidate, has been shown for the first time to induce functional antibodies against both ETEC enterotoxins (STa, LT) produced by all ETEC strains and seven ETEC adhesins (CFA/I, CS1 to CS6) expressed by ETEC strains causing a majority of ETEC diarrhea clinical cases and the moderate-to-severe cases. Moreover, MecVax was demonstrated to protect against ETEC STa or LT toxin-mediated diarrhea in a pig model. If it also protects against ETEC intestinal colonization, MecVax can be validated as an effective ETEC vaccine candidate. This adult rabbit colonization model study showed that intramuscular administration of MecVax effectively prevented intestinal colonization by H10407, perhaps the most virulent ETEC strain, affirming MecVax vaccine candidacy and accelerating vaccine development against ETEC children's diarrhea and travelers' diarrhea.

The role of CFA/I in adherence and toxin delivery by ETEC expressing multiple colonization factors in the human enteroid model

Enterotoxigenic Escherichia coli (ETEC) is a primary causative agent of diarrhea in travelers and young children in low-to-middle-income countries (LMICs). ETEC adhere to intestinal epithelia via colonization factors (CFs) and secrete heat-stable toxin (ST) and/or heat-labile toxin (LT), causing dysregulated cellular ion transport and water secretion. ETEC isolates often harbor genes encoding more than one CF that are targets as vaccine antigens. CFA/I is a major CF that is associated with ETEC that causes moderate-to-severe diarrhea and plays an important role in pathogenesis. The Global Enteric Multicenter Study finding that 78% of CFA/I-expressing ETEC also encode the minor CF CS21 prompted investigation of the combined role of these two CFs. Western blots and electron microscopy demonstrated growth media-dependent and strain-dependent differences in CFA/I and CS21 expression. The critical role of CFA/I in adherence by ETEC strains expressing CFA/I and CS21 was demonstrated using the human enteroid model and a series of CFA/I- and CS21-specific mutants. Furthermore, only anti-CFA/I antibodies inhibited adherence by global ETEC isolates expressing CFA/I and CS21. Delivery of ST and resulting cGMP secretion was measured in supernatants from infected enteroid monolayers, and strain-specific ST delivery and time-dependent cGMP production was observed. Interestingly, cGMP levels were similar across wildtype and CF-deficient strains, reflecting a limitation of this static aerobic infection model. Despite adherence by ETEC and delivery of ST, the enteroid monolayer integrity was not disrupted, as shown by the lack of decrease in transepithelial electrical resistance and the lack of IL-8 cytokines produced during infection. Taken together, these data demonstrate that targeting CFA/I in global clinical CFA/I-CS21 strains is sufficient for adherence inhibition, supporting a vaccine strategy that focuses on blocking major CFs. In addition, the human enteroid model has significant utility for the study of ETEC pathogenesis and evaluation of vaccine-induced functional antibody responses.

Enterotoxigenic Escherichia coli: intestinal pathogenesis mechanisms and colonization resistance by gut microbiota

Enterotoxigenic Escherichia coli (ETEC) is a major cause of diarrhea in children and travelers in developing countries. ETEC is characterized by the ability to produce major virulence factors including colonization factors (CFs) and enterotoxins, that bind to specific receptors on epithelial cells and induce diarrhea. The gut microbiota is a stable and sophisticated ecosystem that performs a range of beneficial functions for the host, including protection against pathogen colonization. Understanding the pathogenic mechanisms of ETEC and the interaction between the gut microbiota and ETEC represents not only a research need but also an opportunity and challenge to develop precautions for ETEC infection. Herein, this review focuses on recent discoveries about ETEC etiology, pathogenesis and clinical manifestation, and discusses the colonization resistances mediated by gut microbiota, as well as preventative strategies against ETEC with an aim to provide novel insights that can reduce the adverse effect on human health.

A multi-epitope fusion antigen candidate vaccine for Enterotoxigenic Escherichia coli is protective against strain B7A colonization in a rabbit model

Enterotoxigenic Escherichia coli (ETEC) strains are a leading cause of children's and travelers' diarrhea. Developing effective vaccines against this heterologous group has proven difficult due to the varied nature of toxins and adhesins that determine their pathology. A multivalent candidate vaccine was developed using a multi-epitope fusion antigen (MEFA) vaccinology platform and shown to effectively elicit broad protective antibody responses in mice and pigs. However, direct protection against ETEC colonization of the small intestine was not measured in these systems. Colonization of ETEC strains is known to be a determining factor in disease outcomes and is adhesin-dependent. In this study, we developed a non-surgical rabbit colonization model to study immune protection against ETEC colonization in rabbits. We tested the ability for the MEFA-based vaccine adhesin antigen, in combination with dmLT adjuvant, to induce broad immune responses and to protect from ETEC colonization of the rabbit small intestine. Our results indicate that the candidate vaccine MEFA antigen elicits antibodies in rabbits that react to seven adhesins included in its construction and protects against colonization of a challenge strain that consistently colonized naïve rabbits.

Oral Immunogenicity of Enterotoxigenic Escherichia coli Outer Membrane Vesicles Encapsulated into Zein Nanoparticles Coated with a Gantrez® AN-Mannosamine Polymer Conjugate

Enterotoxigenic Escherichia coli (ETEC) represents a major cause of morbidity and mortality in the human population. In particular, ETEC infections affect children under the age of five from low-middle income countries. However, there is no licensed vaccine against this pathogen. ETEC vaccine development is challenging since this pathotype expresses a wide variety of antigenically diverse virulence factors whose genes can be modified due to ETEC genetic plasticity. To overcome this challenge, we propose the use of outer membrane vesicles (OMVs) isolated from two ETEC clinical strains. In these OMVs, proteomic studies revealed the presence of important immunogens, such as heat-labile toxin, colonization factors, adhesins and mucinases. Furthermore, these vesicles proved to be immunogenic after subcutaneous administration in BALB/c mice. Since ETEC is an enteropathogen, it is necessary to induce both systemic and mucosal immunity. For this purpose, the vesicles, free or encapsulated in zein nanoparticles coated with a Gantrez®-mannosamine conjugate, were administered orally. Biodistribution studies showed that the encapsulation of OMVs delayed the transit through the gut. These results were confirmed by in vivo study, in which OMV encapsulation resulted in higher levels of specific antibodies IgG2a. Further studies are needed to evaluate the protection efficacy of this vaccine approach.

Intradermally administered enterotoxigenic E. coli vaccine candidate MecVax induces functional serum IgG antibodies against seven adhesins (CFA/I, CS1-CS6) and both toxins (STa, LT)

There are no vaccines licensed for enterotoxigenic Escherichia coli (ETEC), a leading bacterial cause of children's diarrhea and travelers' diarrhea. MecVax, a multivalent E. coli vaccine candidate composed of two epitope- and structure-based polyvalent proteins (toxoid fusion 3xSTa_N12S-mnLT_R192G/L211A and CFA/I/II/IV MEFA), is to induce broad anti-adhesin and antitoxin antibodies against heterogeneous ETEC pathovars. Administered intraperitoneally (IP) or intramuscularly (IM), MecVax was shown to induce antibodies against seven ETEC adhesins (CFA/I, CS1-CS6), which are produced by ETEC pathovars causing over 60% of ETEC-associated diarrheal cases and the moderate-to-severe cases, and both toxins (heat-labile toxin - LT and heat-stable toxin - STa) expressed by all ETEC strains. To further characterize immunogenicity of this protein-based injectable subunit vaccine candidate and to explore other parenteral administration routes for the product, in this study, we intradermally (ID) immunized mice with MecVax and measured antigen-specific antibody responses and further antibody functional activities against the adhesins and toxins targeted by the vaccine. Data showed that mice ID immunized with MecVax developed robust anti-CFA/I, -CS1, -CS2, -CS3, -CS4, -CS5, -CS6, -LT and anti-STa IgG responses. Furthermore, antibodies derived from MecVax via ID route inhibited adherence of ETEC or E. coli strains expressing any of the seven target adhesins (CFA/I, CS1-CS6) and neutralized enterotoxicity of LT and STa toxins. These results confirmed broad immunogenicity of MecVax and suggested that this multivalent ETEC subunit vaccine candidate can be effectively delivered via ID route. IMPORTANCE Enterotoxigenic Escherichia coli (ETEC) is a leading bacterial cause of diarrhea in children living in developing countries and international travelers. Developing an effective vaccine for ETEC diarrhea has been hampered because of challenges of virulence heterogeneity and difficulties of inducing neutralizing antibodies against the key STa toxin. MecVax, a subunit vaccine candidate carrying two polyvalent protein antigens for the first time induces functional antibodies against the most important ETEC adhesins which are associated with a majority of diarrheal cases and the moderate-to-severe cases but also against enterotoxicity of LT and more importantly STa toxin which plays a key role in children's diarrhea and travelers' diarrhea, potentially leading to development of a truly effective ETEC vaccine. Data from this study may also indicated that this ETEC subunit vaccine can be administered effectively via ID route, expanding clinical administration options for this vaccine product.

Genomic Epidemiology and Antimicrobial Susceptibility Profile of Enterotoxigenic Escherichia coli From Outpatients With Diarrhea in Shenzhen, China, 2015-2020

Enterotoxigenic Escherichia coli (ETEC) is the leading cause of severe diarrhea in children and the most common cause of diarrhea in travelers. However, most ETEC infections in Shenzhen, China were from indigenous adults. In this study, we characterized 106 ETEC isolates from indigenous outpatients with diarrhea (77% were adults aged >20 years) in Shenzhen between 2015 and 2020 by whole-genome sequencing and antimicrobial susceptibility testing. Shenzhen ETEC isolates showed a remarkable high diversity, which belonged to four E. coli phylogroups (A: 71%, B1: 13%, E: 10%, and D: 6%) and 15 ETEC lineages, with L11 (25%, O159:H34/O159:H43, ST218/ST3153), novel L2/4 (21%, O6:H16, ST48), and L4 (15%, O25:H16, ST1491) being major lineages. Heat-stable toxin (ST) was most prevalent (76%, STh: 60% STp: 16%), followed by heat-labile toxin (LT, 17%) and ST + LT (7%). One or multiple colonization factors (CFs) were identified in 68 (64%) isolates, with the common CFs being CS21 (48%) and CS6 (34%). Antimicrobial resistance mutation/gene profiles of genomes were concordant with the phenotype testing results of 52 representative isolates, which revealed high resistance rate to nalidixic acid (71%), ampicillin (69%), and ampicillin/sulbactam (46%), and demonstrated that the novel L2/4 was a multidrug-resistant lineage. This study provides novel insight into the genomic epidemiology and antimicrobial susceptibility profile of ETEC infections in indigenous adults for the first time, which further improves our understanding on ETEC epidemiology and has implications for the development of vaccine and future surveillance and prevention of ETEC infections.

Sequence variations in the ETEC CS6 operon affect transcript and protein expression

Enterotoxigenic Escherichia coli (ETEC) is a leading cause of diarrheal disease in developing nations where it accounts for a significant disease burden in children between the ages of 0 to 59 months. It is also the number one bacterial causative agent of traveler’s diarrhea. ETEC infects hosts through the fecal-oral route and utilizes colonization factors (CF) to adhere within the small intestine. Over 25 CFs have been identified; 7 are considered major CFs and a vaccine targeting these is predicted to provide protection against up to 66% of ETEC associated disease. Coli Surface Antigen 6 (CS6) is a major CF and is associated with disease-causing ETEC isolates. Analysis of the CS6 operon sequence led to the identification of two regions of variability among clinical isolates which we predicted exert effects on CS6 transcript and protein expression. A total of 7 recombinant E. coli strains were engineered to encode the CS6 operon in wild-type, hybrid, and mutant configurations. Western blot analysis and RT-qPCR provided evidence to support the importance of an intergenic hairpin structure on CS6 expression. Our results reveal the significance of CS6 sequence selection regarding ETEC vaccine development and present novel information regarding CS6 sequence variation in WT ETEC strains.

Association of enteropathogen detection with diarrhoea by age and high versus low child mortality settings: a systematic review and meta-analysis

BACKGROUND

The odds ratio (OR) comparing pathogen presence in diarrhoeal cases versus asymptomatic controls is a measure for diarrhoeal disease cause that has been integrated into burden of disease estimates across diverse populations. This study aimed to estimate the OR describing the association between pathogen detection in stool and diarrhoea for 15 common enteropathogens by age group and child mortality setting.

METHODS

We did a systematic review to identify case-control and cohort studies published from Jan 1, 1990, to July 9, 2019, which examined at least one enteropathogen of interest and the outcome diarrhoea. The analytical dataset included data extracted from published articles and supplemented with data from the Global Enteric Multicenter Study and the Malnutrition and Enteric Disease study. Random effects meta-analysis models were fit for each enteropathogen, stratified by age group and child mortality level, and adjusted for pathogen detection method and study design to produce summary ORs describing the association between pathogen detection in stool and diarrhoea.

FINDINGS

1964 records were screened and 130 studies (over 88 079 cases or diarrhoea samples and 135 755 controls or non-diarrhoea samples) were available for analysis. Heterogeneity (I2) in unadjusted models was substantial, ranging from 27·6% to 86·6% across pathogens. In stratified and adjusted models, summary ORs varied by age group and setting, ranging from 0·4 (95% CI 0·2-0·6) for Giardia lamblia to 54·1 (95% CI 7·4-393·5) for Vibrio cholerae.

INTERPRETATION

Incorporating effect estimates from diverse data sources into diarrhoeal disease cause and burden of disease models is needed to produce more representative estimates.

FUNDING

WHO, Bill & Melinda Gates Foundation, and National Institutes of Health.

Confronting challenges to enterotoxigenic Escherichia coli vaccine development

The enterotoxigenic Escherichia coli (ETEC) are a diverse and genetically plastic pathologic variant (pathovar) of E. coli defined by their production of heat-labile (LT) and heat-stable (ST) enterotoxins. These pathogens, which came to recognition more than four decades ago in patients presenting with severe cholera-like diarrhea, are now known to cause hundreds of millions of cases of symptomatic infection annually. Children in low-middle income regions of the world lacking access to clean water and basic sanitation are disproportionately affected by ETEC. In addition to acute diarrheal morbidity, these pathogens remain a significant cause of mortality in children under the age of five years and have also been linked repeatedly to sequelae of childhood malnutrition and growth stunting. Vaccines that could prevent ETEC infections therefore remain a high priority. Despite several decades of effort, a licensed vaccine that protects against the breadth of these pathogens remains an aspirational goal, and the underlying genetic plasticity of E. coli has posed a fundamental challenge to development of a vaccine that can encompass the complete antigenic spectrum of ETEC. Nevertheless, novel strategies that include toxoids, a more complete understanding of ETEC molecular pathogenesis, structural details of target immunogens, and the discovery of more highly conserved antigens essential for virulence should accelerate progress and make a broadly protective vaccine feasible.

Safety and immunogenicity of intramuscularly administered CS6 subunit vaccine with a modified heat-labile enterotoxin from enterotoxigenic Escherichia coli

INTRODUCTION

Enterotoxigenic Escherichia coli (ETEC) is a common cause of infectious diarrhoea and a leading cause of morbidity and mortality in children living in resource-limited settings. It is also the leading cause of travellers' diarrhoea among civilian and military travellers. Its dual importance in global public health and travel medicine highlights the need for an effective vaccine. ETEC express colonization factors (CFs) that mediate adherence to the small intestine. An epidemiologically prevalent CF is coli surface antigen 6 (CS6). We assessed the safety and immunogenicity of a CS6-targeted candidate vaccine, CssBA, co-administered intramuscularly with the double-mutant heat-labile enterotoxin, dmLT [LT(R192G/L211A)].

METHODS

This was an open-label trial. Fifty subjects received three intramuscular injections (Days 1, 22 and 43) of CssBA alone (5 µg), dmLT alone (0.1 µg) or CssBA (5, 15, 45 µg) + dmLT (0.1 and 0.5 µg). Subjects were actively monitored for adverse events for 28 days following the third vaccination. Antibody responses (IgG and IgA) were characterized in the serum and from lymphocyte supernatants (ALS) to CS6 and the native ETEC heat labile enterotoxin, LT.

RESULTS

Across all dose cohorts, the vaccine was safe and well-tolerated with no vaccine-related severe or serious adverse events. Among vaccine-related adverse events, a majority (98%) were mild with 79% being short-lived vaccine site reactions. Robust antibody responses were induced in a dose-dependent manner with a clear dmLT adjuvant effect. Response rates in subjects receiving 45 µg CssBA and 0.5 µg dmLT ranged from 50 to 100% across assays.

CONCLUSION

This is the first study to demonstrate the safety and immunogenicity of CssBA and/or dmLT administered intramuscularly. Co-administration of the two components induced robust immune responses to CS6 and LT, paving the way for future studies to evaluate the efficacy of this vaccine target and development of a multivalent, subunit ETEC vaccine.

Virulence Factors of Enteric Pathogenic Escherichia coli: A Review

Escherichia coli are remarkably versatile microorganisms and important members of the normal intestinal microbiota of humans and animals. This harmless commensal organism can acquire a mixture of comprehensive mobile genetic elements that contain genes encoding virulence factors, becoming an emerging human pathogen capable of causing a broad spectrum of intestinal and extraintestinal diseases. Nine definite enteric E. coli pathotypes have been well characterized, causing diseases ranging from various gastrointestinal disorders to urinary tract infections. These pathotypes employ many virulence factors and effectors subverting the functions of host cells to mediate their virulence and pathogenesis. This review summarizes new developments in our understanding of diverse virulence factors associated with encoding genes used by different pathotypes of enteric pathogenic E. coli to cause intestinal and extraintestinal diseases in humans.

Structure of the master regulator Rns reveals an inhibitor of enterotoxigenic Escherichia coli virulence regulons

Enteric infections caused by the gram-negative bacteria enterotoxigenic Escherichia coli (ETEC), Vibrio cholerae, Shigella flexneri, and Salmonella enterica are among the most common and affect billions of people each year. These bacteria control expression of virulence factors using a network of transcriptional regulators, some of which are modulated by small molecules as has been shown for ToxT, an AraC family member from V. cholerae. In ETEC the expression of many types of adhesive pili is dependent upon the AraC family member Rns. We present here the 3 Å crystal structure of Rns and show it closely resembles ToxT. Rns crystallized as a dimer via an interface similar to that observed in other dimeric AraC's. Furthermore, the structure of Rns revealed the presence of a ligand, decanoic acid, that inhibits its activity in a manner similar to the fatty acid mediated inhibition observed for ToxT and the S. enterica homologue HilD. Together, these results support our hypothesis that fatty acids regulate virulence controlling AraC family members in a common manner across a number of enteric pathogens. Furthermore, for the first time this work identifies a small molecule capable of inhibiting the ETEC Rns regulon, providing a basis for development of therapeutics against this deadly human pathogen.

Development and Comparison of a Panel of Modified CS17 Fimbrial Tip Adhesin Proteins as Components for an Adhesin-Based Vaccine against Enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is a leading cause of diarrhea in travelers and children in resource-limited countries. ETEC colonization factors, fimbrial tip adhesins and enterotoxins are key virulence factors, and thus have been studied as vaccine candidates. Some prevalent colonization factors, including CFA/I and CS17, belong to the class 5 family. We previously found that passive oral administration of hyperimmune bovine colostral IgG (bIgG) raised against dscCfaE (donor strand complemented CFA/I tip adhesin) protected volunteers against CFA/I⁺ ETEC challenge, while anti-dscCsbD bIgG (CS17 tip adhesin) did not confer protection. These findings led us to develop and optimize a panel of alternative CsbD-based vaccine candidates based on allele matching and in silico protein engineering. Physicochemical characterizations revealed that an optimized vaccine candidate dscCsbD_LSN139(P218A/G3) had the greatest thermal stability among the six tested dscCsbD adhesins, whereas the overall secondary structures and solubility of these adhesins had no obvious differences. Importantly, dscCsbD_LSN139(P218A/G3) elicited significantly higher CS17⁺ ETEC hemagglutination inhibition titers in sera from mice intranasally immunized with the panel of dscCsbD adhesins, while no significant difference was observed among heterologous neutralizing titers. Our results strongly advocate for the incorporation of these modifications into a new generation of CsbD-based ETEC vaccine candidates.

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

Diarrhoeal disease attributable to enterotoxigenic Escherichia coli (ETEC) causes substantial morbidity and mortality predominantly in paediatric populations in low- and middle-income countries. In addition to acute illness, there is an increasing appreciation of the long-term consequences of enteric infections, including ETEC, on childhood growth and development. Provision of potable water and sanitation and appropriate clinical care for acute illness are critical to reduce the ETEC burden. However, these interventions are not always practical and may not achieve equitable and sustainable coverage. Vaccination may be the most cost-effective and equitable means of primary prevention; however, additional data are needed to accelerate the investment and guide the decision-making process for ETEC vaccines. First, to understand and quantify the ETEC disease burden, additional data are needed on the association between ETEC infection and physical and cognitive stunting as well as delayed educational attainment. Furthermore, the role of inappropriate or inadequate antibiotic treatment of ETEC-attributable diarrhoea may contribute to the development of antimicrobial resistance (AMR) and needs further elucidation. An ETEC vaccine that mitigates acute diarrhoeal illness and minimizes the longer-term disease manifestations could have significant public health impact and be a cost-effective countermeasure. Herein we review the ETEC vaccine pipeline, led by candidates compatible with the general parameters of the Preferred Product Characteristics (PPC) recently developed by the World Health Organization. Additionally, we have developed an ETEC Vaccine Development Strategy to provide a framework to underpin priority activities for researchers, funders and vaccine manufacturers, with the goal of addressing globally unmet data needs in the areas of research, product development, and policy, as well as commercialization and delivery. The strategy also aims to guide prioritization and co-ordination of the priority activities needed to minimize the timeline to licensure and use of ETEC vaccines, especially in in low- and middle-income countries, where they are most urgently needed.

Distribution of virulence factors and its relatedness towards the antimicrobial response of enterotoxigenic Escherichia coli strains isolated from patients in Kolkata, India

AIM

Enterotoxigenic Escherichia coli (ETEC) is one of the most widely recognized diarrhoeal pathogens in developing countries. The advancement of ETEC vaccine development depends on the antigenic determinants of the ETEC isolates from a particular geographical region. So, the aim here was to comprehend the distribution of virulence determinants of the clinical ETEC strains of this region. Additionally, an attempt was made to find any correlation with the antimicrobial response pattern.

METHODS AND RESULTS

Multiplex PCR was employed to identify virulence determinants followed by confirmatory singleplex PCR. For observation of antibiotic response, the Kirby-Bauer method was used. Out of 379 strains, 46% of strains harboured both the enterotoxins ST and LT, whereas 15% were LT only. Among the major colonization factors (CFs), CS6 (41%) was the most prevalent followed by CFA/I (35%) and CFA/III was the lowest (3%). Among the minor CFs, CS21 (25%) was most prevalent, while CS15 showed the lowest (3%) presence. Among the non-classical virulence factors, EatA (69%) was predominant. ETEC strains harbouring CS6 showed resistance towards the commonly used drug Ciprofloxacin (70%).

CONCLUSION

CS6 and elt+est toxin genes co-occurred covering 51% of the isolates. CS21 was found in most strains with est genes (43%). EatA was found to occur frequently when ST was present alone or with LT. CS6-harbouring strains showed an independent correlation to antimicrobial resistance.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study would aid in identifying the commonly circulating ETEC isolates of Kolkata, India, and their prevalent virulence determinants. Knowledge of antibiotic resistance patterns would also help in the appropriate use of antibiotics. Furthermore, the study would aid in identifying the multivalent antigens suitable for region-specific ETEC vaccines with maximum coverage.

Updates on defining and detecting diarrheagenic Escherichia coli pathotypes

PURPOSE OF REVIEW

Several types of Escherichia coli cause acute diarrhea in humans and are responsible for a large burden of disease globally. The purpose of this review is to summarize diarrheagenic Escherichia coli (DEC) pathotype definitions and discuss existing and emerging molecular, genomic, and gut microbiome methods to detect, define, and study DEC pathotypes.

RECENT FINDINGS

DEC pathotypes are currently diagnosed by molecular detection of unique virulence genes. However, some pathotypes have defied coherent molecular definitions because of imperfect gene targets, and pathotype categories are complicated by hybrid strains and isolation of pathotypes from asymptomatic individuals. Recent progress toward more efficient, sensitive, and multiplex DEC pathotype detection has been made using emerging PCR-based technologies. Genomics and gut microbiome detection methods continue to advance rapidly and are contributing to a better understanding of DEC pathotype diversity and functional potential.

SUMMARY

DEC pathotype categorizations and detection methods are useful but imperfect. The implementation of molecular and sequence-based methods and well designed epidemiological studies will continue to advance understanding of DEC pathotypes. Additional emphasis is needed on sequencing DEC genomes from regions of the world where they cause the most disease and from the pathotypes that cause the greatest burden of disease globally.

Protection From Natural Immunity Against Enteric Infections and Etiology-Specific Diarrhea in a Longitudinal Birth Cohort

BACKGROUND

The degree of protection conferred by natural immunity is unknown for many enteropathogens, but it is important to support the development of enteric vaccines.

METHODS

We used the Andersen-Gill extension of the Cox model to estimate the effects of previous infections on the incidence of subsequent subclinical infections and diarrhea in children under 2 using quantitative molecular diagnostics in the MAL-ED cohort. We used cross-pathogen negative control associations to correct bias due to confounding by unmeasured heterogeneity of exposure and susceptibility.

RESULTS

Prior rotavirus infection was associated with a 50% lower hazard (calibrated hazard ratio [cHR], 0.50; 95% confidence interval [CI], 0.41-0.62) of subsequent rotavirus diarrhea. Strong protection was evident against Cryptosporidium diarrhea (cHR, 0.32; 95% CI, 0.20-0.51). There was also protection due to prior infections for norovirus GII (cHR against diarrhea, 0.67; 95% CI, 0.49-0.91), astrovirus (cHR, 0.62; 95% CI, 0.48-0.81), and Shigella (cHR, 0.79; 95% CI, 0.65-0.95). Minimal protection was observed for other bacteria, adenovirus 40/41, and sapovirus.

CONCLUSIONS

Natural immunity was generally stronger for the enteric viruses than bacteria, potentially due to less antigenic diversity. Vaccines against major causes of diarrhea may be feasible but likely need to be more immunogenic than natural infection.

Establishment and Validation of Pathogenic CS17+ and CS19+ Enterotoxigenic Escherichia coli Challenge Models in the New World Primate Aotus nancymaae

Enterotoxigenic Escherichia coli (ETEC) is a common cause of diarrheal illness in the military, travelers, and children living in low- to middle-income countries. Increased antibiotic resistance, the absence of a licensed vaccine, and the lack of broadly practical therapeutics perpetuate the significant health and financial burden resulting from ETEC infection. A critical step in the evaluation of vaccines and therapeutics is preclinical screening in a relevant animal disease model that closely replicates human disease. We previously developed a diarrheal model of class 5a colonization factor (CF) CFA/I-expressing ETEC in the New World owl monkey species Aotus nancymaae using ETEC strain H10407. In order to broaden the use of the model, we report here on the development of A. nancymaae models of ETEC expressing the class 5b CFs CS17 and CS19 with strains LSN03-016011/A and WS0115A, respectively. For both models, we observed diarrheal attack rates of ≥80% after oral inoculation with 5 × 10¹¹ CFU of bacteria. These models will aid in assessing the efficacy of future ETEC vaccine candidates and therapeutics.

Anti-CfaE nanobodies provide broad cross-protection against major pathogenic enterotoxigenic Escherichia coli strains, with implications for vaccine design

Enterotoxigenic Escherichia coli (ETEC) is estimated to cause approximately 380,000 deaths annually during sporadic or epidemic outbreaks worldwide. Development of vaccines against ETEC is very challenging due to the vast heterogeneity of the ETEC strains. An effective vaccines would have to be multicomponent to provide coverage of over ten ETEC strains with genetic variabilities. There is currently no vaccine licensed to prevent ETEC. Nanobodies are successful new biologics in treating mucosal infectious disease as they recognize conserved epitopes on hypervariable pathogens. Cocktails consisting of multiple nanobodies could provide even broader epitope coverage at a lower cost compared to monoclonal antibodies. Identification of conserved epitopes by nanobodies can also assist reverse engineering of an effective vaccine against ETEC. By screening nanobodies from immunized llamas and a naïve yeast display library against adhesins of colonization factors, we identified single nanobodies that show cross-protective potency against eleven major pathogenic ETEC strains in vitro. Oral administration of nanobodies led to a significant reduction of bacterial colonization in animals. Moreover, nanobody-IgA fusion showed extended inhibitory activity in mouse colonization compared to commercial hyperimmune bovine colostrum product used for prevention of ETEC-induced diarrhea. Structural analysis revealed that nanobodies recognized a highly-conserved epitope within the putative receptor binding region of ETEC adhesins. Our findings support further rational design of a pan-ETEC vaccine to elicit robust immune responses targeting this conserved epitope.

Description of Enteropathic Escherichia coli Species in Pediatric Patients at a Quaternary Children's Hospital

BACKGROUND

The epidemiology, demographics, clinical presentations, and outcomes associated with enteroaggregative Escherichia coli (EAEC), enteropathogenic E. coli (EPEC), and enterotoxigenic E. coli (ETEC) pathotypes in US children are not well understood.

METHODS

This study was a retrospective chart review of all pediatric patients with a stool sample submitted to the Children's Hospital Colorado clinical microbiology laboratory for testing with the BioFire FilmArray Gastrointestinal Pathogen Panel from October 2015 through October 2017.

RESULTS

During the study period, 5692 patient stool samples were submitted; 679 (13%) were positive for EAEC, EPEC, or ETEC. Of note, 163/232 (70%) patients with EAEC, 282/493 (57%) with EPEC, and 49/58 (85%) with ETEC had detection of at least 1 other pathogen. Of all E. coli-positive stool samples, only 158/679 (23%) were from low-risk patients who were singly infected with EAEC, EPEC, or ETEC. In this cohort, most cases were associated with acute diarrhea (50%), abdominal pain (61%), and/or cramping (49%) and presented without fever (14%), emesis (28%), or lethargy (7%). Thirteen (8%) of these 158 patients received antibiotics at the time of their initial presentation to care. Of the 145 patients who did not receive antibiotics at their initial visit, 23 (16%) returned to care due to persistence of symptoms.

CONCLUSIONS

Our results suggest that the majority of patients singly infected with EAEC, EPEC, or ETEC present with mild, self-limited, gastrointestinal (GI) complaints. Further research is needed to determine what role these pathogens might play in children who present with chronic or inflammatory GI symptoms.