Expression and purification of the recombinant enteropathogenic Escherichia coli vaccine candidates BfpA and EspB

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.

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.

Recent advances in understanding enteric pathogenic Escherichia coli

Although Escherichia coli can be an innocuous resident of the gastrointestinal tract, it also has the pathogenic capacity to cause significant diarrheal and extraintestinal diseases. Pathogenic variants of E. coli (pathovars or pathotypes) cause much morbidity and mortality worldwide. Consequently, pathogenic E. coli is widely studied in humans, animals, food, and the environment. While there are many common features that these pathotypes employ to colonize the intestinal mucosa and cause disease, the course, onset, and complications vary significantly. Outbreaks are common in developed and developing countries, and they sometimes have fatal consequences. Many of these pathotypes are a major public health concern as they have low infectious doses and are transmitted through ubiquitous mediums, including food and water. The seriousness of pathogenic E. coli is exemplified by dedicated national and international surveillance programs that monitor and track outbreaks; unfortunately, this surveillance is often lacking in developing countries. While not all pathotypes carry the same public health profile, they all carry an enormous potential to cause disease and continue to present challenges to human health. This comprehensive review highlights recent advances in our understanding of the intestinal pathotypes of E. coli.

Suitability of a recombinant Staphylococcus aureus enterotoxin C bovine variant for immunodiagnostics and therapeutic vaccine development

Recombinant bovine variant of staphylococcal enterotoxin C (SECbovine), produced as a NH2-terminal histidine hexamer fusion protein (His6-tagged SECbovine), expressed at high levels (25%) in Escherichia coli and affinity purified to homogeneity (99.9%), was tested for its diagnostic and therapeutic potentials. His6-tagged SECbovine is antigenically authentic to native SECbovine across host species, as confirmed by antibody-based capture detection assays using human, mouse, rabbit and chicken hyperimmune sera. His6-tagged SECbovine showed significant T-cell stimulation activity in vitro. His6-tagged SECbovine was immunogenic for IgG in mice (intragastric and intravenous routes) and rabbits (intramuscular and subcutaneous routes), dispensing immunoadjuvant coadministration. The formation of neutralizing antibodies reduced the severity of intoxication symptoms in immunized rabbits. Purified anti-recombinant SECbovine rabbit polyclonal IgG neutralized the pyrexic and diarrhoeagenic effects of native SEC/SED and recombinant SEC, tested by the kitten and rabbit bioassays, respectively.

Egg yolk anti-BfpA antibodies as a tool for recognizing and identifying enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) is a major aetiological agent of childhood diarrhoea in developing countries. The structural repeating protein A subunit, BfpA, found in the bundle-forming pilus, is one of the virulent factors for EPEC pathogenesis. Recombinant BfpA in laying hens elicited sustained and vigorous antibody production. Immunoglobulin Y (IgY) anti-BfpA antibodies were recovered from egg yolk, purified and characterized. Immunoadsorption with whole extracts of the isogenic E. coli EPEC adherence factor (EAF) strain that lacks BfpA rendered the resulting IgY preparations capable of: (a) recognizing purified or recombinant BfpA proteins in a dose-dependent fashion; (b) blocking the colonization of HeLa cells by EPEC EAF+, in vitro; (c) specifically identifying E. coli bearing EAF+; and (d) inhibiting the growth of E. coli EAF+ but not the EAF strain. IgY anti-BfpA is potentially useful as a specific, low-cost immunobiological reagent to screen human faecal specimens for the presence of EPEC.

Coproantibodies to the enteropathogenic Escherichia coli vaccine candidates BfpA and EspB in breastfed and artificially fed children

A diagnostic test was developed to discriminate active from past enteropathogenic Escherichia coli (EPEC) infection, which uses the affinity-purified recombinant proteins BfpA (bundle-forming pilus (BFP) structural repeating subunit A) and EspB (pore-forming secreted protein B) as reliable markers of virulence to detect antigen-specific coproantibodies by immunoblot analysis, and verification of active typical EPEC infection by gene-specific (bfpA and espB) PCR amplification using DNA extracted directly from specimens and/or culture-enriched preparations. To begin addressing the potential protective role of anti-EPEC antibodies at early age, the prevalence of IgA coproantibodies to these antigens was determined in either breastfed or artificially fed children <2 years of age hospitalized for watery diarrhea.