Murine immunization with CS21 pili or LngA major subunit of enterotoxigenic Escherichia coli (ETEC) elicits systemic and mucosal immune responses and inhibits ETEC gut colonization

Recombinant Escherichia coli BL21 with LngA Variants from ETEC E9034A Promotes Adherence to HT-29 Cells

The CS21 pilus produced by enterotoxigenic Escherichia coli (ETEC) is involved in adherence to HT-29 intestinal cells. The CS21 pilus assembles proteins encoded by 14 genes clustered into the lng operon.

AIM

This study aimed to determine whether E. coli BL21 (ECBL) transformed with the lng operon lacking the lngA gene (pE9034AΔlngA) and complemented in trans with lngA variants of ETEC clinical strains, as well as point substitutions, exhibited modified adherence to HT-29 cells.

METHODS

A kanamycin cassette was used to replace the lngA gene in the lng operon of the E9034A strain, and the construct was transformed into the ECBL strain. The pJET1.2 vector carrying lngA genes with allelic variants was transformed into ECBLpE9034AΔlngA (ECBLΔlngA). The point substitutions were performed in the pJETlngA_FMU073332 vector.

RESULTS

Bioinformatic alignment analysis of the LngA proteins showed hypervariable regions and clustered the clinical ETEC strains into three groups. Variations in amino acid residues affect the adherence percentages of recombinant ECBL strains with lngA variants and site-specific mutations with HT-29 cells.

CONCLUSION

In this study, ECBL carrying the lng operon harboring lngA variants of six clinical ETEC strains, as well as point substitutions, exerted an effect on the adherence of ECBL to HT-29 cells, thereby confirming the importance of the CS21 pilus in adherence.

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.

In silico Designing of an Epitope-Based Vaccine Against Common E. coli Pathotypes

Escherichia coli (E. coli) is a Gram-negative bacterium that belongs to the family Enterobacteriaceae. While E. coli can stay as an innocuous resident in the digestive tract, it can cause a group of symptoms ranging from diarrhea to live threatening complications. Due to the increased rate of antibiotic resistance worldwide, the development of an effective vaccine against E. coli pathotypes is a major health priority. In this study, a reverse vaccinology approach along with immunoinformatics has been applied for the detection of potential antigens to develop an effective vaccine. Based on our screening of 5,155 proteins, we identified lipopolysaccharide assembly protein (LptD) and outer membrane protein assembly factor (BamA) as vaccine candidates for the current study. The conservancy of these proteins in the main E. coli pathotypes was assessed through BLASTp to make sure that the designed vaccine will be protective against major E. coli pathotypes. The multitope vaccine was constructed using cytotoxic T lymphocyte (CTL), helper T lymphocyte (HTL), and B cell lymphocyte (BCL) epitopes with suitable linkers and adjuvant. Following that, it was analyzed computationally where it was found to be antigenic, soluble, stable, and non-allergen. Additionally, the adopted docking study, as well as all-atom molecular dynamics simulation, illustrated the promising predicted affinity and free binding energy of this constructed vaccine against the human Toll-like receptor-4 (hTLR-4) dimeric state. In this regard, wet lab studies are required to prove the efficacy of the potential vaccine construct that demonstrated promising results through computational validation.

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

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

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.

Effects of IQW and IRW on Inflammation and Gut Microbiota in ETEC-Induced Diarrhea

Methods

The mice were randomly distributed into four groups: (a) control (CTRL) group, (b) ETEC group, (c) IQW-ETEC group, and (d) IRW-ETEC group. Villus length and crypt depth were measured after hematoxylin and eosin staining. The inflammatory reaction was analyzed via inflammatory cytokines (i.e., TNF-α, IL-1β, IL-6, and IL-10) using the enzyme-linked immunosorbent assay (ELISA). The microbiota in the colon was sequenced using 16S ribosomal RNA.

Results

The villus length decreased, the crypt depth decreased, and the expression of inflammatory cytokines (i.e., TNF-α, IL-1β, IL-6, and IL-10) increased due to ETEC. In the IRW-ETEC and IQW-ETEC groups, the Shannon index decreased (P < 0.05). IQW and IRW increased the abundance of Firmicutes, Proteobacteria, Clostridiales, Lachnospiraceae, and Alloprevotella; contrastingly, it decreased the abundance of Epsilonproteobacteria, Erysipelotrichales, Prevotellaceae, and Flavobacteriaceae compared to the ETEC group (P <0.05).

Conclusion

This study ascertained that the addition of IQW and IRW could alleviate jejunal inflammation and increase microbiota community diversity.

Intestinal Pathogenic Escherichia coli: Insights for Vaccine Development

Diarrheal diseases are one of the major causes of mortality among children under five years old and intestinal pathogenic Escherichia coli (InPEC) plays a role as one of the large causative groups of these infections worldwide. InPECs contribute significantly to the burden of intestinal diseases, which are a critical issue in low- and middle-income countries (Asia, Africa and Latin America). Intestinal pathotypes such as enteropathogenic E. coli (EPEC) and enterotoxigenic E. coli (ETEC) are mainly endemic in developing countries, while ETEC strains are the major cause of diarrhea in travelers to these countries. On the other hand, enterohemorrhagic E. coli (EHEC) are the cause of large outbreaks around the world, mainly affecting developed countries and responsible for not only diarrheal disease but also severe clinical complications like hemorrhagic colitis and hemolytic uremic syndrome (HUS). Overall, the emergence of antibiotic resistant strains, the annual cost increase in the health care system, the high incidence of traveler diarrhea and the increased number of HUS episodes have raised the need for effective preventive treatments. Although the use of antibiotics is still important in treating such infections, non-antibiotic strategies are either a crucial option to limit the increase in antibiotic resistant strains or absolutely necessary for diseases such as those caused by EHEC infections, for which antibiotic therapies are not recommended. Among non-antibiotic therapies, vaccine development is a strategy of choice but, to date, there is no effective licensed vaccine against InPEC infections. For several years, there has been a sustained effort to identify efficacious vaccine candidates able to reduce the burden of diarrheal disease. The aim of this review is to summarize recent milestones and insights in vaccine development against InPECs.