Isolation, affinity purification, and identification of piglet small intestine mucosa receptor for enterotoxigenic Escherichia coli k88ac+ fimbriae

Evaluation of inhibition of F4ac positive Escherichia coli attachment with xanthine dehydrogenase, butyrophilin, lactadherin and fatty acid binding protein

Background

Neonatal and post-weaning colibacillosis caused by enterotoxigenic E. coli is responsible for substantial economic losses encountered by the pork industry. Intestinal colonization of young piglets by E. coli depends on the efficiency of bacterial attachment to host gastrointestinal epithelium that is mediated by fimbriae. We tested the effect of porcine individual milk fat globule membrane (MFGM) proteins on F4ac positive E. coli attachment to porcine enterocytes in vitro.

Results

Butyrophilin, lactadherin and fatty acid binding protein inhibited fimbriae-dependent adherence of E. coli to enterocytes in vitro, while xanthine dehydrogenase did not. The inhibiting activity was dose-dependent for all three proteins, but the inhibiting efficiency was different.

Conclusions

The results indicate that MFGM proteins may interfere with attachment of E. coli to porcine neonatal intestinal mucosa.

Identification of Escherichia coli F4ac-binding proteins in porcine milk fat globule membrane

F4ac-positive enterotoxigenic Escherichia coli (ETEC) must attach to the intestinal mucosa to cause diarrhea in piglets. Prevention of bacterial attachment to the intestinal mucosa is the most effective defense against ETEC-induced diarrhea. Porcine milk fat globule membranes (MFGM) were shown to be able to inhibit attachment of ETEC to the intestinal brush border; however, the specific components of porcine MFGM that inhibited attachment of ETEC to enterocytes were not identified. Accordingly, the purpose of this study was to identify F4ac-binding MFGM proteins by overlay Western blot and affinity chromatography. The proteome of porcine MFGM was characterized and the following F4ac-binding proteins were detected by overlay Western blot and affinity chromatography: lactadherin, butyrophilin, adipophilin, acyl-CoA synthetase 3, and fatty acid-binding protein 3. The biological function of these proteins was not investigated but it is possible that their interaction with F4ac fimbria interferes with bacterial attachment and colonization.

Screening the ability of natural feed ingredients to interfere with the adherence of enterotoxigenicEscherichia coli(ETEC) K88 to the porcine intestinal mucus

The inhibition of the attachment of bacteria to the intestine by receptor analogues could be a novel approach to prevent enterotoxigenicEscherichia coli(ETEC) K88-induced diarrhoea in piglets. The objective of the present study was to screen the ability of different feed ingredients (FI) to bind to ETEC K88 (adhesion test, AT) and to block its attachment to the porcine intestinal mucus (blocking test, BT) usingin vitromicrotitration-based models. In the AT, wheat bran (WB), casein glycomacropeptide (CGMP) and exopolysaccharides exhibited the highest adhesion to ETEC K88 (P< 0·001). In the BT, WB, CGMP and locust bean (LB) reduced the number of ETEC K88 attached to the intestinal mucus (P< 0·001). For WB and LB, fractionation based on their carbohydrate components was subsequently carried out, and each fraction was evaluated individually. None of the WB fractions reduced the adhesion of ETEC K88 to the mucus as did the original extract, suggesting that a protein or glycoprotein could be involved in the recognition process. With regard to the LB fractions, the water-extractable material reduced the adhesion of ETEC K88 (P< 0·001) to the mucus similar to the original extract (P< 0·001), indicating, in this case, that galactomannans or phenolic compounds could be responsible for the recognition process. In conclusion, among the FI screened, the soluble extracts obtained from WB, LB and CGMP exhibited the highest anti-adhesive properties against ETEC K88 in the BT. These results suggest that they may be good candidates to be included in diets of weaned piglets for the prevention of ETEC K88-induced diarrhoea.

Transfer of Cystoisospora suis-specific colostral antibodies and their correlation with the course of neonatal porcine cystoisosporosis

Cystoisospora suis is the most pathogenic species of coccidia in suckling piglets, affecting them predominantly within their first three weeks of life. The clinical signs of neonatal cystoisosporosis include watery diarrhea and wasting, leading to significant economic losses for the farmer. Since neonatal piglets have an immature immune system, colostral transfer of maternal factors such as immune cells or antibodies is essential for controlling infections at that age. However, the role of C. suis-specific antibodies transferred from the sow to the piglets and possible correlations between antibody levels in the piglets acquired from colostrum with the clinical outcome of disease are currently not understood. To address this issue, 12 non-infected piglets and 14 piglets experimentally infected with C. suis on the third day of life were examined during their first four weeks of life. IgG, IgA, and IgM titers in the blood serum specific for sporozoites and merozoites of C. suis were evaluated, along with oocyst excretion and fecal consistency. Additionally, the antibody content in the colostrum and milk of three mother sows was determined. A transfer of naturally acquired C. suis-specific antibodies from sows to piglets with the colostrum could be demonstrated. Maternal antibodies in piglets' blood sera did not persist for longer than 14-21 days except for IgG which was present in high titers until the end of the study. Within 2-3 weeks after birth the onset of endogenous antibody production was noticed. Titers in blood serum showed a correlation with the severity of diarrhea which was positive for IgG and IgM (possibly due to increased consumption or loss of these antibodies) and negative for IgA. C. suis-specific mucus antibodies isolated from infected and non-infected piglets (n=6/group) on the 28th day of life were present in both groups, showing significantly higher titers of IgA and IgM in infected piglets. Maternally transferred antibodies acquired by natural infections of sows as observed in this study did not provide protection against the clinical manifestation of disease. The level and effect of transferrable maternal factors necessary for protection still need to be elucidated. However, correlations between antibody titers and fecal consistency in the piglets indicate that C. suis-specific antibodies might be useful markers for the expectable clinical severity of cystoisosporosis.

Saccharomyces cerevisiae modulates immune gene expressions and inhibits ETEC-mediated ERK1/2 and p38 signaling pathways in intestinal epithelial cells

BACKGROUND

Enterotoxigenic Escherichia coli (ETEC) infections result in large economic losses in the swine industry worldwide. ETEC infections cause pro-inflammatory responses in intestinal epithelial cells and subsequent diarrhea in pigs, leading to reduced growth rate and mortality. Administration of probiotics as feed additives displayed health benefits against intestinal infections. Saccharomyces cerevisiae (Sc) is non-commensal and non-pathogenic yeast used as probiotic in gastrointestinal diseases. However, the immuno-modulatory effects of Sc in differentiated porcine intestinal epithelial cells exposed to ETEC were not investigated.

METHODOLOGY/PRINCIPAL FINDINGS

We reported that the yeast Sc (strain CNCM I-3856) modulates transcript and protein expressions involved in inflammation, recruitment and activation of immune cells in differentiated porcine intestinal epithelial IPEC-1 cells. We demonstrated that viable Sc inhibits the ETEC-induced expression of pro-inflammatory transcripts (IL-6, IL-8, CCL20, CXCL2, CXCL10) and proteins (IL-6, IL-8). This inhibition was associated to a decrease of ERK1/2 and p38 MAPK phosphorylation, an agglutination of ETEC by Sc and an increase of the anti-inflammatory PPAR-γ nuclear receptor mRNA level. In addition, Sc up-regulates the mRNA levels of both IL-12p35 and CCL25. However, measurement of transepithelial electrical resistance displayed that Sc failed to maintain the barrier integrity in monolayer exposed to ETEC suggesting that Sc does not inhibit ETEC enterotoxin activity.

CONCLUSIONS

Sc (strain CNCM I-3856) displays multiple immuno-modulatory effects at the molecular level in IPEC-1 cells suggesting that Sc may influence intestinal inflammatory reaction.

Lactobacillus fermentum BCS87 expresses mucus- and mucin-binding proteins on the cell surface

AIMS

To identify and characterize adhesion-associated proteins in the potential probiotic Lactobacillus fermentum BCS87.

METHODS AND RESULTS

Protein suspensions obtained from the treatment of Lact. fermentum BCS87 with 1 mol 1(-1) LiCl were analysed by Western blotting using HRP-labelled porcine mucus and mucin. Two adhesion-associated proteins with relative molecular weight of 29 and 32 kDa were identified. The N-terminal and internal peptides of the 32 kDa protein (32-Mmubp) were sequenced, and the corresponding gene (32-mmub) was found by inverse polymerase chain reaction. The complete nucleotide sequence of 32-mmub revealed an open reading frame of 903 bp encoding a primary protein of 300 amino acids and a mature protein of 272 residues. A basic local alignment search showed 47-99% identity to solute-binding components of ATP binding cassette transporter proteins in Lactobacillus, Streptococcus and Clostridium. An OpuAC-conserved domain was identified and phylogenetic relationship analysis confirmed that 32-Mmubp belongs to the OpuAC family.

CONCLUSIONS

Adhesion of Lact. fermentum BCS87 appeared to be mediated by two surface-associated proteins. 32-Mmubp is a component of ABC transporter system that also functions as an adhesin.

SIGNIFICANCE AND IMPACT OF THE STUDY

Characterization of 32-Mmubp and 32-mmub will contribute to understanding the host-bacteria interactions of Lact. fermentum with the intestinal tract of pigs.

Intestinal adherence of Vibrio cholerae involves a coordinated interaction between colonization factor GbpA and mucin

The chitin-binding protein GbpA of Vibrio cholerae has been recently described as a common adherence factor for chitin and intestinal surface. Using an isogenic in-frame gbpA deletion mutant, we first show that V. cholerae O1 El Tor interacts with mouse intestinal mucus quickly, using GbpA in a specific manner. The gbpA mutant strain showed a significant decrease in intestinal adherence, leading to less colonization and fluid accumulation in a mouse in vivo model. Purified recombinant GbpA (rGbpA) specifically bound to N-acetyl-D-glucosamine residues of intestinal mucin in a dose-dependent, saturable manner with a dissociation constant of 11.2 microM. Histopathology results from infected mouse intestine indicated that GbpA binding resulted in a time-dependent increase in mucus secretion. We found that rGbpA increased the production of intestinal secretory mucins (MUC2, MUC3, and MUC5AC) in HT-29 cells through upregulation of corresponding genes. The upregulation of MUC2 and MUC5AC genes was dependent on NF-kappaB nuclear translocation. Interestingly, mucin could also increase GbpA expression in V. cholerae in a dose-dependent manner. Thus, we propose that there is a coordinated interaction between GbpA and mucin to upregulate each other in a cooperative manner, leading to increased levels of expression of both of these interactive factors and ultimately allowing successful intestinal colonization and pathogenesis by V. cholerae.

Isolation and identification of AIDA-I receptors in porcine intestinal mucus

Porcine AIDA-I positive Escherichia coli causes diarrhea in neonatal piglets and AIDA-I adhesin is an important virulence factor involved in intestinal colonization with biofilm formation. This biofilm consists of AIDA-I(+)E. coli bacteria stratified within mucus layers covering the intestinal mucosa. Based on the intimate interaction between AIDA-I(+)E. coli and mucus within the intestinal biofilm, we hypothesized that porcine intestinal mucus contains receptor(s) for AIDA-I adhesin. Since porcine AIDA-I receptors have not been identified, we employed affinity chromatography and in vitro adhesion assays to investigate AIDA-I binding proteins in porcine intestinal mucus that might serve as receptors for attachment of AIDA-I positive E. coli. We demonstrated that porcine mucus contains 65 and 120kDa proteins (p65 and p120) that bind with high affinity to purified AIDA-I adhesin and that AIDA-I positive E. coli binds to these proteins with higher affinity than do AIDA-I negative mutant. The identity of p65 was not determined based on LC-MS/MS data, whereas p120 was matched to two nuclear proteins (namely, DNA damage binding protein and splicing factor 3b) and one cytoplasmic protein, which is an IgG Fc binding protein. Based on similar amino acid homology, molecular weight, structural similarity to mucin and reported evidence of being secreted by goblet cells into the intestinal lumen, we think that the IgG Fc binding protein is most likely candidate to serve as a potential receptor in intestinal mucus for AIDA-I adhesin.

Identification by mass spectroscopy of F4ac-fimbrial-binding proteins in porcine milk and characterization of lactadherin as an inhibitor of F4ac-positive Escherichia coli attachment to intestinal villi in vitro

Enterotoxigenic Escherichia coli (ETEC) must attach to the intestinal surface to cause diarrhea. Milk and colostrum play an important role in protecting suckling piglets against ETEC through their constituent antibodies as well as non-immunoglobulin factors. We used affinity chromatography and liquid chromatography-mass spectrometry to identify lactadherin, beta-casein, whey acidic protein, lipoprotein lipase, and several structural cellular proteins as non-immunoglobulin F4ac fimbriae-binding porcine milk proteins. To determine their potential biological relevance in a digestive environment, we treated porcine milk with pepsin or pepsin-pancreating in vitro, and found that pepsin digestion did not interfere with the F4-binding capacity of lactadherin as well as it revealed a cryptic F4-binding site(s) in alpha-S(1) casein and heart fatty acid binding protein. We also demonstrated that lactadherin interfered with attachment of F4ac-positive ETEC to porcine small intestinal villi in vitro and that this interference was carbohydrate dependent. Thus, our evidence suggests that lactadherin and the other F4-binding milk proteins, together with other defense components of milk, could play a role in protection of neonatal piglets against ETEC induced diarrhea.

A plasmid DNA encoding chicken interleukin-6 and Escherichia coli K88 fimbrial protein FaeG stimulates the production of anti-K88 fimbrial antibodies in chickens

Immunization using a plasmid to deliver an encoded protein for expression in situ as the antigen is a promising technology. A plasmid encoding the enterotoxigenic Escherichia coli K88 fimbrial protein FaeG when injected into chickens stimulates the production of antibodies against the fimbrial protein, similar to what has been observed in mice. The efficacy of a genetic adjuvant on fimbrial antibody production was tested by introducing the gene for chicken interleukin-6 in tandem with the faeG gene. Expression of both the fimbrial FaeG protein and chicken interleukin-6 protein was confirmed in COS-M6 cells. Slightly higher antiFaeG antibody titer in chickens was obtained compared with immunization with the plasmid encoding FaeG alone, especially at 10 (19%, P < 0.05) and 12 (27%, P < 0.05) wk, respectively, after the secondary immunization. Elevated antiFaeG antibody titer induced by chicken interleukin-6 and FaeG proteins expressed jointly persisted longer than when induced by FaeG protein alone. This is the first report of an avian cytokine enhancing an immune response, and confirms that coexpression of the antigen and adjuvant from a plasmid delivered by DNA immunization is an effective protocol.

Heat shock protein 60 acts as a receptor for the Listeria adhesion protein in Caco-2 cells

The 104-kDa Listeria adhesion protein (LAP) in Listeria monocytogenes is involved in binding to various mammalian cell lines. However, the receptor that interacts with LAP in eukaryotic cells is unknown. In this study, scanning immunoelectron microscopy qualitatively demonstrated greater binding capacity of wild-type (WT) L. monocytogenes strain (F4244) than a LAP-deficient mutant strain (KB208) to Caco-2 cells. The goal of this study was identification of the host cell receptor for LAP. Using a Western blot ligand overlay assay, we identified a protein of 58 kDa to be the putative receptor for LAP from Caco-2 cells. N-terminal sequencing and subsequent database search identified this protein as heat shock protein 60 (Hsp60). Modified immunoseparation with protein A-Sepharose beads bound to the LAP-specific monoclonal antibody H7 (MAb-H7) and a sequential incubation with LAP preparation and Caco-2 lysate confirmed the receptor to be the same 58-kDa protein. Western blot analysis with anti-Hsp60 MAb of whole-cell adhesion between Caco-2 and WT also revealed the receptor protein to be a 58-kDa protein, thus corroborating the identification of Hsp60 as a host cell receptor for LAP. Furthermore, the anti-Hsp60 antibody also caused approximately 74% reduction in binding of L. monocytogenes WT to Caco-2 cells, whereas a control antibody, C11E9, had no effect on binding. The adhesion mechanism of L. monocytogenes to eukaryotic cells is a complex process, and identification of Hsp60 as a receptor for LAP adds to the list of previously discovered ligand-receptor modules that are essential to achieve successful adhesion.

Inhibition of adhesion of Escherichia coli k88ac fimbria to its receptor, intestinal mucin-type glycoproteins, by a monoclonal antibody directed against a variable domain of the fimbria

Strains of enterotoxigenic Escherichia coli that express K88 fimbriae are among the most common causes of diarrhea in young pigs. Adhesion of bacteria to receptors on intestinal epithelial cells, mediated by K88 fimbriae, is the initial step in the establishment of infection. Three antigenic variants of K88 fimbriae exist in nature: K88ab, K88ac, and K88ad. K88ac is the most prevalent and may be the only variant of significance in swine disease. Each K88 fimbrial variant is composed of multiple antigenic determinants. Some of these determinants are shared among the three variants and may be referred to as conserved epitopes, whereas others are unique to a specific variant and may be referred to as variable epitopes. In this study, monoclonal antibodies (MAbs) specific to either variable or conserved epitopes of K88ac fimbriae were produced. The specificity of each MAb was tested by enzyme-linked immunosorbent and immunoblot assays. Fab fragments were prepared from these MAbs and were tested for their ability to block the binding of K88-positive bacteria and purified fimbriae to porcine enterocyte brush border vesicles and purified K88 receptors, respectively. The purified receptors were intestinal mucin-type sialoglycoproteins (IMTGP) isolated from porcine enterocytes (A. K. Erickson, D. R. Baker, B. T. Bosworth, T. A. Casey, D. A. Benfield, and D. H. Francis, Infect. Immun. 62:5404-5410, 1994). Fab fragments prepared from MAbs specific for variable epitopes blocked the binding of bacteria to brush borders and of fimbriae to IMTGP. However, those from MAbs specific for a conserved epitope did not. These observations indicate that the receptor-binding domain of a K88ac fimbria is contained, at least in part, within the antigenically variable epitopes of that fimbria. Epitope mapping for one of the MAbs, which recognizes a linear epitope on K88ac fimbriae, indicated that this MAb binds to the region from amino acid no. 64 to no. 107 on the major subunit of K88ac fimbriae.