Conserved regions in the sequence of the F4 (K88) fimbrial adhesin FaeG suggest a donor strand mechanism in F4 assembly

Lactoferrin Decreases Enterotoxigenic Escherichia coli-Induced Fluid Secretion and Bacterial Adhesion in the Porcine Small Intestine

Enterotoxigenic Escherichia coli (ETEC) infections are one of the most prevalent causes of post-weaning diarrhea in piglets, resulting in morbidity, mortality and elevated use of antibiotics. The emergence and further spread of antimicrobial resistance together with the growing demand for high quality animal protein requires the identification of novel alternatives for antimicrobials. A promising alternative is lactoferrin, as we previously showed that it can both inhibit the growth and degrade bacterial virulence factors of porcine ETEC strains in vitro. Aiming to confirm these findings in vivo, we performed a small intestinal segment perfusion experiment in piglets. Here, we showed that lactoferrin could not only decrease ETEC-induced fluid secretion, but also their ability to colonize the small intestinal epithelium. Furthermore, while ETEC infection induced pro-inflammatory cytokine mRNA expression in this experiment, lactoferrin was not able to counteract these responses. In addition, a bacterial motility assay showed that lactoferrin can reduce the motility of ETEC. Our findings further support the use of lactoferrin as an alternative for antimicrobials and also show its potential for the prevention of ETEC infections in pigs.

Seroepidemiological survey on pigs and cattle for novel K88 (F4)-like colonisation factor detected in human enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) strains that express various fimbrial or nonfimbrial colonisation factors (CFs) and enterotoxins are critical causes of diarrhoeal diseases. Human ETEC serotype O169:H41 (O169) has been a representative of epidemic ETEC worldwide; the organism shows massive adherence to HEp-2 cells similar to enteroaggregative E. coli. Previously, we determined the complete sequence of the unstable virulence plasmid, pEntYN10. The plasmid included a unique set of genes encoding a novel CF resembling K88 (F4) of porcine ETEC, in addition to CS6, a well-known representative CF of human ETEC, and another novel CF similar to CS8 (CFA/III) of human ETEC. In the present study, we focused on K88-like CF (hereafter, K88_O169) that may allow the organisms to infect domestic livestock like original K88-harbouring strains that can cause diarrhoea in piglets. Samples were tested for antibodies against recombinant proteins of possible paralogous adhesins, FaeG1 and FaeG2, from K88_O169 and the FaeG of typical K88 (F4). The seroepidemiological study using recombinant antigens (two paralogs FaeG1 and FaeG2 from K88_O169) showed reactivity of porcine (18.0%) and bovine (17.1%) sera to K88_O169 FaeG1 and/or FaeG2 antigens on indirect ELISA tests. These results suggest that E. coli with K88_O169 adhesin can infect various hosts, including pigs and cattle. This is the first report of domestic livestock having antibodies to K88_O169 of human ETEC. Although human ETEC had been thought to be distinguished from those of domestic animals based on CFs, zoonotic strains may conceal themselves among human ETEC organisms. The concept of One Health should be adopted to intervene in ETEC infections among animals and humans.

Porcine and Bovine Forms of Lactoferrin Inhibit Growth of Porcine Enterotoxigenic Escherichia coli and Degrade Its Virulence Factors

Postweaning diarrhea (PWD) is an economically important, multifactorial disease affecting pigs within the first 2 weeks after weaning. The most common agent associated with PWD is enterotoxigenic Escherichia coli (ETEC). Currently, antibiotics are used to control PWD, and this has most likely contributed to an increased prevalence of antibiotic-resistant strains. This puts pressure on veterinarians and farmers to decrease or even abandon the use of antibiotics, but these measures need to be supported by alternative strategies for controlling these infections. Naturally derived molecules, such as lactoferrin, could be potential candidates due to their antibacterial or immune-modulating activities. Here, we analyzed the ability of bovine lactoferrin (bLF), porcine lactoferrin (pLF), and ovotransferrin (ovoTF) to inhibit ETEC growth, degrade ETEC virulence factors, and inhibit adherence of these pathogens to porcine intestinal epithelial cells. Our results revealed that bLF and pLF, but not ovoTF, inhibit the growth of ETEC. Furthermore, bLF and pLF can degrade several virulence factors produced by ETEC strains, more specifically F4 fimbriae, F18 fimbriae, and flagellin. On the other hand, ovoTF degrades F18 fimbriae and flagellin but not F4 fimbriae. An in vitro adhesion assay showed that bLF, ovoTF, and pLF can decrease the number of bacteria adherent to epithelial cells. Our findings demonstrate that lactoferrin can directly affect porcine ETEC strains, which could allow lactoferrin to serve as an alternative to antimicrobials for the prevention of ETEC infections in piglets.IMPORTANCE Currently, postweaning F4⁺ and F18⁺ Escherichia coli infections in piglets are controlled by the use of antibiotics and zinc oxide, but the use of these antimicrobial agents most likely contributes to an increase in antibiotic resistance. Our work demonstrates that bovine and porcine lactoferrin can inhibit the growth of porcine enterotoxigenic E. coli strains. In addition, we also show that lactoferrin can reduce the adherence of these strains to small intestinal epithelial cells, even at a concentration that does not inhibit bacterial growth. This research could allow us to develop lactoferrin as an alternative strategy to prevent enterotoxigenic E. coli (ETEC) infections in piglets.

Binding determinants in the interplay between porcine aminopeptidase N and enterotoxigenic Escherichia coli F4 fimbriae

The binding of F4⁺ enterotoxigenic Escherichia coli (ETEC) and the specific receptor on porcine intestinal epithelial cells is the initial step in F4⁺ ETEC infection. Porcine aminopeptidase N (APN) is a newly discovered receptor for F4 fimbriae that binds directly to FaeG adhesin, which is the major subunit of the F4 fimbriae variants F4ab, F4ac, and F4ad. We used overlapping peptide assays to map the APN-FaeG binding sites, which has facilitated in the identifying the APN-binding amino acids that are located in the same region of FaeG variants, thereby limiting the major binding regions of APN to 13 peptides. To determine the core sequence motif, a panel of FaeG peptides with point mutations and FaeG mutants were constructed. Pull-down and binding reactivity assays using piglet intestines determined that the amino acids G159 of F4ab, N209 and L212 of F4ac, and A200 of F4ad were the critical residues for APN binding of FaeG. We further show using ELISA and confocal microscopy assay that amino acids 553–568, and 652–670 of the APN comprise the linear epitope for FaeG binding in all three F4 fimbriae variants.

Characterization of unstable pEntYN10 from enterotoxigenic Escherichia coli (ETEC) O169:H41

Enterotoxigenic Escherichia coli (ETEC) serotype O169:H41 has been an extremely destructive epidemic ETEC type worldwide. The strain harbors a large unstable plasmid that is regarded as responsible for its virulence, although its etiology has remained unknown. To examine its genetic background specifically on the unstable retention and responsibility in the unique adherence to epithelial cells and enterotoxin production, the complete sequence of a plasmid, pEntYN10, purified from the serotype strain was determined. The length is 145,082 bp; its GC content is 46.15%. It contains 182 CDSs, which include 3 colonization factors (CFs), an enterotoxin, and large number of insertion sequences. The repertory of plasmid stability genes was extraordinarily scant. Uniquely, results showed that 3 CFs, CS6, CS8 (CFA/III)-like, and K88 (F4)-like were encoded redundantly in the plasmid with unique variations among previously known subtypes. These three CFs preserved their respective gene structures similarly to those of other ETEC strains reported previously with unique sequence variations respectively. It is particularly interesting that the K88-like gene cluster of pEntYN10 had 2 paralogous copies of faeG, which encodes the major component of fimbrial structure. It remains to be verified how the unique variations found in the CFs respectively affect the affinity to infected cells, host range, and virulence of the ETEC strain.

Animal Enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is the most common cause of E. coli diarrhea in farm animals. ETEC are characterized by the ability to produce two types of virulence factors: adhesins that promote binding to specific enterocyte receptors for intestinal colonization and enterotoxins responsible for fluid secretion. The best-characterized adhesins are expressed in the context of fimbriae, such as the F4 (also designated K88), F5 (K99), F6 (987P), F17, and F18 fimbriae. Once established in the animal small intestine, ETEC produce enterotoxin(s) that lead to diarrhea. The enterotoxins belong to two major classes: heat-labile toxins that consist of one active and five binding subunits (LT), and heat-stable toxins that are small polypeptides (STa, STb, and EAST1). This review describes the disease and pathogenesis of animal ETEC, the corresponding virulence genes and protein products of these bacteria, their regulation and targets in animal hosts, as well as mechanisms of action. Furthermore, vaccines, inhibitors, probiotics, and the identification of potential new targets by genomics are presented in the context of animal ETEC.

Porcine aminopeptidase N binds to F4+ enterotoxigenic Escherichia coli fimbriae

F4⁺ enterotoxigenic Escherichia coli (ETEC) strains cause diarrheal disease in neonatal and post-weaned piglets. Several different host receptors for F4 fimbriae have been described, with porcine aminopeptidase N (APN) reported most recently. The FaeG subunit is essential for the binding of the three F4 variants to host cells. Here we show in both yeast two-hybrid and pulldown assays that APN binds directly to FaeG, the major subunit of F4 fimbriae, from three serotypes of F4⁺ ETEC. Modulating APN gene expression in IPEC-J2 cells affected ETEC adherence. Antibodies raised against APN or F4 fimbriae both reduced ETEC adherence. Thus, APN mediates the attachment of F4⁺E. coli to intestinal epithelial cells.

F4+ enterotoxigenic Escherichia coli (ETEC) adhesion mediated by the major fimbrial subunit FaeG

The FaeG subunit is the major constituent of F4(+) fimbriae, associated with glycoprotein and/or glycolipid receptor recognition and majorly contributes to the pathogen attachment to the host cells. To investigate the key factor involved in the fimbrial binding of F4(+) Escherichia coli, both the recombinant E. coli SE5000 strains carrying the fae operon gene clusters that express the different types of fimbriae in vitro, named as rF4ab, rF4ac, and rF4ad, respectively, corresponding to the fimbrial types F4ab, F4ac, and F4ad, and the three isogenic in-frame faeG gene deletion mutants were constructed. The adhesion assays and adhesion inhibition assays showed that ΔfaeG mutants had a significant reduction in the binding to porcine brush border as well as the intestinal epithelial cell lines, while the complemented strain ΔfaeG/pfaeG restored the adhesion function. The recombinant bacterial strains rF4ab, rF4ac, and rF4ad have the same binding property as wild-type F4(+) E. coli strains do and improvement in terms of binding to porcine brush border and the intestinal epithelial cells, and the adherence was blocked by the monoclonal antibody anti-F4 fimbriae. These data demonstrate that the fimbrial binding of F4(+) E. coli is directly mediated by the major FaeG subunit.

Production of a subunit vaccine candidate against porcine post-weaning diarrhea in high-biomass transplastomic tobacco

Post-weaning diarrhea (PWD) in piglets is a major problem in piggeries worldwide and results in severe economic losses. Infection with Enterotoxigenic Escherichia coli (ETEC) is the key culprit for the PWD disease. F4 fimbriae of ETEC are highly stable proteinaceous polymers, mainly composed of the major structural subunit FaeG, with a capacity to evoke mucosal immune responses, thus demonstrating a potential to act as an oral vaccine against ETEC-induced porcine PWD. In this study we used a transplastomic approach in tobacco to produce a recombinant variant of the FaeG protein, rFaeG(ntd/dsc), engineered for expression as a stable monomer by N-terminal deletion and donor strand-complementation (ntd/dsc). The generated transplastomic tobacco plants accumulated up to 2.0 g rFaeG(ntd/dsc) per 1 kg fresh leaf tissue (more than 1% of dry leaf tissue) and showed normal phenotype indistinguishable from wild type untransformed plants. We determined that chloroplast-produced rFaeG(ntd/dsc) protein retained the key properties of an oral vaccine, i.e. binding to porcine intestinal F4 receptors (F4R), and inhibition of the F4-possessing (F4+) ETEC attachment to F4R. Additionally, the plant biomass matrix was shown to delay degradation of the chloroplast-produced rFaeG(ntd/dsc) in gastrointestinal conditions, demonstrating a potential to function as a shelter-vehicle for vaccine delivery. These results suggest that transplastomic plants expressing the rFaeG(ntd/dsc) protein could be used for production and, possibly, delivery of an oral vaccine against porcine F4+ ETEC infections. Our findings therefore present a feasible approach for developing an oral vaccination strategy against porcine PWD.

Erythrocyte and porcine intestinal glycosphingolipids recognized by F4 fimbriae of enterotoxigenic Escherichia coli

Enterotoxigenic F4-fimbriated Escherichia coli is associated with diarrheal disease in neonatal and postweaning pigs. The F4 fimbriae mediate attachment of the bacteria to the pig intestinal epithelium, enabling an efficient delivery of diarrhea-inducing enterotoxins to the target epithelial cells. There are three variants of F4 fimbriae designated F4ab, F4ac and F4ad, respectively, having different antigenic and adhesive properties. In the present study, the binding of isolated F4ab, F4ac and F4ad fimbriae, and F4ab/ac/ad-fimbriated E. coli, to glycosphingolipids from erythrocytes and from porcine small intestinal epithelium was examined, in order to get a comprehensive view of the F4-binding glycosphingolipids involved in F4-mediated hemagglutination and adhesion to the epithelial cells of porcine intestine. Specific interactions between the F4ab, F4ac and F4ad fimbriae and both acid and non-acid glycosphingolipids were obtained, and after isolation of binding-active glycosphingolipids and characterization by mass spectrometry and proton NMR, distinct carbohydrate binding patterns were defined for each fimbrial subtype. Two novel glycosphingolipids were isolated from chicken erythrocytes, and characterized as GalNAcα3GalNAcß3Galß4Glcß1Cer and GalNAcα3GalNAcß3Galß4GlcNAcß3Galß4Glcß1Cer. These two compounds, and lactosylceramide (Galß4Glcß1Cer) with phytosphingosine and hydroxy fatty acid, were recognized by all three variants of F4 fimbriae. No binding of the F4ad fimbriae or F4ad-fimbriated E. coli to the porcine intestinal glycosphingolipids occurred. However, for F4ab and F4ac two distinct binding patterns were observed. The F4ac fimbriae and the F4ac-expressing E. coli selectively bound to galactosylceramide (Galß1Cer) with sphingosine and hydroxy 24:0 fatty acid, while the porcine intestinal glycosphingolipids recognized by F4ab fimbriae and the F4ab-fimbriated bacteria were characterized as galactosylceramide, sulfatide (SO(3)-3Galß1Cer), sulf-lactosylceramide (SO(3)-3Galß4Glcß1Cer), and globotriaosylceramide (Galα4Galß4Glcß1Cer) with phytosphingosine and hydroxy 24:0 fatty acid. Finally, the F4ad fimbriae and the F4ad-fimbriated E. coli, but not the F4ab or F4ac subtypes, bound to reference gangliotriaosylceramide (GalNAcß4Galß4Glcß1Cer), gangliotetraosylceramide (Galß3GalNAcß4Galß4Glcß1Cer), isoglobotriaosylceramide (Galα3Galß4Glcß1Cer), and neolactotetraosylceramide (Galß4GlcNAcß3Galß4Glcß1Cer).

Enterotoxigenic Escherichia coli (K88) induce proinflammatory responses in porcine intestinal epithelial cells

Infections with F4(+) enterotoxigenic Escherichia coli (ETEC) causes severe diarrhoea in piglets, resulting in morbidity and mortality. F4 fimbriae are the key virulence factors mediating the attachment of F4(+) ETEC to the intestinal epithelium. Intestinal epithelial cells (IEC) are recently being recognized as important regulators of the intestinal immune system through the secretion of cytokines, however, data on how F4(+) ETEC affect this cytokine secretion are scarce. By using ETEC strains expressing either polymeric, monomeric or F4 fimbriae with a reduced polymeric stability, we demonstrated that polymeric fimbriae are essential for adhesion to porcine IEC and the secretion of IL-6 and IL-8 by IEC. Remarkably, this cytokine secretion was not abrogated following stimulation with an F4-negative strain. Since this strain expresses flagellin, TLR5 mediated signalling could be involved. Indeed, porcine IEC express TLR5 and purified flagellin induced IL-6 and IL-8 secretion, indicating that, as for other pathogens, flagellin is the dominant virulence factor involved in the induction of proinflammatory responses in IEC. These results indicate a potential mucosal adjuvant capacity of ETEC-derived flagellin and may improve rational vaccine design against F4(+) ETEC infections.

Immune responses elicited in mice with recombinant Lactococcus lactis expressing F4 fimbrial adhesin FaeG by oral immunization

Enterotoxigenic Escherichia coli (ETEC) is a major pathogenic agent causing piglet diarrhea. The major subunit and adhesin FaeG of F4(+) ETEC is an important virulence factor with strong immunogenicity. To determine whether Lactococcus lactis (L. lactis) could effectively deliver FaeG to the mucosal immune system, recombinant L. lactis expressing FaeG was constructed, and immune responses in mice following oral route delivery of recombinant L. lactis were explored. The production of FaeG expressed in L. lactis was up to approximately 10% of soluble whole-cell proteins, and recombinant FaeG (rFaeG) possessed good immunoreactivity by Western blot analysis. Oral immunization with recombinant L. lactis expressing FaeG induced F4-specific mucosal and systemic immune responses in the mice. In addition, high dose recombinant L. lactis or co-administration of high dose recombinant L. lactis with CTB enhanced the immune responses. These results suggested that L. lactis expressing FaeG was a promising candidate vaccine against ETEC.

Structural and thermodynamic characterization of pre- and postpolymerization states in the F4 fimbrial subunit FaeG

Enterotoxigenic Escherichia coli expressing F4 fimbriae are the major cause of porcine colibacillosis and are responsible for significant death and morbidity in neonatal and postweaned piglets. Via the chaperone-usher pathway, F4 fimbriae are assembled into thin, flexible polymers mainly composed of the single-domain adhesin FaeG. The F4 fimbrial system has been labeled eccentric because the F4 pilins show some features distinct from the features of pilins of other chaperone-usher-assembled structures. In particular, FaeG is much larger than other pilins (27 versus approximately 17 kDa), grafting an additional carbohydrate binding domain on the common immunoglobulin-like core. Structural data of FaeG during different stages of the F4 fimbrial biogenesis process, combined with differential scanning calorimetry measurements, confirm the general principles of the donor strand complementation/exchange mechanisms taking place during pilus biogenesis via the chaperone-usher pathway.

The excretion of F18+ E. coli is reduced after oral immunisation of pigs with a FedF and F4 fimbriae conjugate

Currently, no vaccines are available for edema disease and post-weaning diarrhoea (PWD) in pigs. In the present study, a subunit vaccine containing the F18 fimbrial adhesin FedF was studied. Hereto, recombinant FedF was produced as a fusion protein with maltose-binding protein. Even though the produced MBPFedF was shown to attach in vitro to enterocytes, almost no FedF-specific immune response could be detected after oral administration to piglets. The delivery of FedF to the intestinal mucosa was improved by conjugating the MBPFedF to F4 fimbriae. Indeed, this conjugation induced a systemic and local FedF-specific immune response and led to a reduction in excretion after infection with F18+ E. coli. Although complete protection was not observed, the conjugation between FedF and F4 fimbriae can be considered as a first step towards the development of a combined vaccine against F4+ and F18+ E. coli infections.

Chloroplasts assemble the major subunit FaeG of Escherichia coli F4 (K88) fimbriae to strand-swapped dimers

F4 fimbriae encoded by the fae operon are the major colonization factors associated with porcine neonatal and postweaning diarrhoea caused by enterotoxigenic Escherichia coli (ETEC). Via the chaperone/usher pathway, the F4 fimbriae are assembled as long polymers of the major subunit FaeG, which also possesses the adhesive properties of the fimbriae. Intrinsically, the incomplete fold of fimbrial subunits renders them unstable and susceptible to aggregation and/or proteolytic degradation in the absence of a specific periplasmic chaperone. In order to test the possibility of producing FaeG in plants, FaeG expression was studied in transgenic tobacco plants. FaeG was directed to different subcellular compartments by specific targeting signals. Targeting of FaeG to the chloroplast results in much higher yields than FaeG targeting to the endoplasmic reticulum or the apoplast. Two chloroplast-targeted FaeG variants were purified from tobacco plants and crystallized. The crystal structures show that chloroplasts circumvent the absence of the fimbrial assembly machinery by assembling FaeG into strand-swapped dimers. Furthermore, the structures reveal how FaeG combines the structural requirements of a major fimbrial subunit with its adhesive role by grafting an additional domain on its Ig-like core.

Comparison of immune responses in parenteral FaeG DNA primed pigs boosted orally with F4 protein or reimmunized with the DNA vaccine

We previously showed that an intradermal (i.d.) FaeG DNA prime (2x)-oral F4 protein boost immunization induces a systemic response and weakly primes a mucosal IgG response in pigs, especially when plasmid vectors encoding the A and B subunit of the E. coli thermo-labile enterotoxin (LT) are added to the DNA vaccine. In the present study, we evaluated whether addition of 1alpha,25-dihydroxyvitamin D(3) (vitD(3)) to the DNA vaccine could further enhance this mucosal priming and/or modulate the antibody response towards IgA. To further clarify priming of systemic and mucosal responses by the i.d. DNA vaccination, we firstly compared the localization of the F4-specific antibody response in pigs that were orally boosted with F4 to that in pigs that received a third i.d. DNA immunization and secondly evaluated cytokine mRNA expression profiles after i.d. DNA vaccination. The i.d. DNA prime (2x)-oral F4 boost immunization as well as the 3 i.d. DNA vaccinations induced mainly a systemic response, with a higher response observed following the heterologous protocol. Co-administration of vitD(3), and especially of the LT vectors, enhanced this response. Furthermore, only the heterologous immunization resulted in a weak mucosal priming, which appeared to require the presence of the LT vectors or vitD(3) as adjuvants. In addition, the LT vectors strongly enhanced the FaeG-specific lymphocyte proliferation and this was accompanied by the absence of a clear IL-10 response. However, despite two DNA immunizations in the presence of these adjuvants and an oral F4 boost, we failed to demonstrate the secretory IgA response needed to be protective against enterotoxigenic E. coli.

Glycosylated F4 (K88) fimbrial adhesin FaeG expressed in barley endosperm induces ETEC-neutralizing antibodies in mice

The F4-positive enterotoxigenic Escherichia coli (ETEC) strains are a frequent cause of porcine post-weaning diarrhea. Orally administered F4 fimbriae or FaeG, the major subunit and adhesin of F4, induce a protective mucosal immune response in F4 receptor-positive piglets. Feed plants carrying immunogenic subunit proteins can offer great advantages for oral vaccination of domestic animals. Here, we describe high-level endosperm-specific production (1% of total soluble proteins) of FaeG in the crop plant barley. The endoplasmic reticulum-targeted recombinant endospermic FaeG (erFaeG) was shown to be heterogeneously glycosylated. The erFaeG showed resistance at digestive conditions simulating piglet gastric fluid. Glycosylation did not abolish the immunogenic character of the FaeG protein, since erFaeG was able to induce F4 fimbria-specific antibodies in mice. Biological activity of these anti-F4 antibodies was demonstrated in vitro by blocking the attachment of the F4+ ETEC to the F4 receptors present on porcine intestinal enterocytes.

Optimized FaeG expression and a thermolabile enterotoxin DNA adjuvant enhance priming of an intestinal immune response by an FaeG DNA vaccine in pigs

One of the problems hindering the development of DNA vaccines is the relatively low immunogenicity often seen in humans and large animals compared to that in mice. In the present study, we tried to enhance the immunogenicity of a pcDNA1/faeG19 DNA vaccine in pigs by optimizing the FaeG expression plasmid and by coadministration of the plasmid vectors encoding the A and B subunits of the Escherichia coli thermolabile enterotoxin (LT). The insertion of a Kozak sequence and optimization of vector (cellular localization and expression) and both vector and codon usage were all shown to enhance in vitro FaeG expression compared to that of pcDNA1/faeG19. Subsequently, pcDNA1/faeG19 and the vector-optimized and the vector-codon-optimized construct were tested for their immunogenicity in pigs. In line with the in vitro results, antibody responses were better induced with increasing expression. The LT vectors additionally enhanced the antibody response, although not significantly, and were necessary to induce an F4-specific cellular response. These vectors were also added because LT has been described to direct the systemic response towards a mucosal immunoglobulin A (IgA) response in mice. Here, however, the intradermal FaeG DNA prime-oral F4 boost immunization resulted in a mainly systemic IgG response, with only a marginal but significant reduction in F4+ E. coli fecal excretion when the piglets were primed with pWRGFaeGopt and pWRGFaeGopt with the LT vectors.

F4 (K88) fimbrial adhesin FaeG expressed in alfalfa reduces F4+ enterotoxigenic Escherichia coli excretion in weaned piglets

Transgenic plants are attractive bioreactors to large-scale production of recombinant proteins because of their relatively low cost. This study reports for the first time the use of transgenic plants to reduce enterotoxigenic Escherichia coli (ETEC) excretion in its natural host species. The DNA sequence encoding the major subunit and adhesin FaeG of F4+ ETEC was transformed into edible alfalfa plants. Targeting of FaeG production to chloroplasts led to FaeG levels of up to 1% of the total soluble protein fraction of the transgenic alfalfa. Recombinant plant-produced FaeG (pFaeG) remained stable for 2 years when the plant material was dried and stored at room temperature. Intragastric immunization of piglets with pFaeG induced a weak F4-specific humoral response. Co-administration of pFaeG and the mucosal adjuvant cholera toxin (CT) enhanced the immune response against FaeG, reflected a better induction of an F4-specific immune response. In addition, the intragastric co-administration of CT with pFaeG significantly reduced F4+ E. coli excretion following F4+ ETEC challenge as compared with pigs that had received nontransgenic plant material. In conclusion, transgenic plants producing the FaeG subunit protein could be used for production and delivery of oral vaccines against F4+ ETEC infections.

F4 fimbriae expressed by porcine enterotoxigenic Escherichia coli, an example of an eccentric fimbrial system?

An overwhelming number of infectious diseases in both humans and animals are initiated by bacterial adhesion to carbohydrate structures on a mucosal surface. Most bacterial pathogens mediate this adhesion by fimbriae or pili which contain an adhesive lectin subunit. The importance of fimbriae as virulence factors led to research elucidating the regulation of fimbrial expression and their molecular assembly process. This review provides an overview of the current knowledge of induction, expression and assembly of F4 (K88) fimbriae and discusses its unique as well as its identical characteristics compared to other intensively studied fimbriae or pili expressed by Escherichia coli.