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PubMed1983

Serologic differentiation between antitoxin responses to infection with Vibrio cholerae and enterotoxin-producing Escherichia coli.

A ganglioside enzyme-linked immunosorbent assay (ELISA) was used to study and attempt to differentiate between antitoxin responses in persons infected with either Vibrio cholerae or Escherichia coli producing heat-labile enterotoxin. In most cases (69%-94%), experimentally infected North Americans and naturally infected Bangladeshis responded to either infection with significant (greater than twofold) increases in serum antibody titer to both heat-labile enterotoxin and cholera toxin. In all but one instance, the response was higher to the homologous than to the heterologous toxin, and for the Americans the homologous antitoxin titers remained significantly higher for at least one year. Determination of levels of antibodies to purified subunits A and B of cholera toxin by an ELISA showed that V. cholerae infection in most instances induced a significant response to subunit B but rarely to subunit A. E. coli infection, on the other hand, induced only slight increases in antibody titer to either subunit.

Adolescent↗

PubMed1984

A simple, sensitive, and specific assay for the heat-stable enterotoxin of Escherichia coli.

A simple assay for the heat-stable enterotoxin (ST) of Escherichia coli was developed on the basis of ST activation of guanylate cyclase in membranes from the intestinal mucosa of mice. ST activated guanylate cyclase in mucosal membranes in a linear fashion over a 50-fold range of toxin concentrations with Mg++-guanosine 5'-triphosphate as substrate. Activation of guanylate cyclase was detectable at concentrations of ST that were five- to 10-fold lower than those resulting in increases in the ratio of gut weight to carcass weight of mice. This assay was used to quantify ST in crude and purified samples from culture filtrates of wild-type strains and recombinant strains of E coli containing the gene for ST. Activation of guanylate cyclase was specific for ST; purified cholera toxin and E coli heat-labile enterotoxin did not activate guanylate cyclase. Thus, this assay for ST is sensitive, specific, and will facilitate rapid analysis of samples for quantification of ST.

Animals↗

PubMed1995

Prevalence of Shigella enterotoxin 1 among Shigella clinical isolates of diverse serotypes.

Shigella enterotoxin 1 (ShET1) is a novel, iron-dependent, toxin encoded by chromosomal genes (set1). To determine the prevalence of this enterotoxin, 172 Shigella clinical isolates (and 10 enteroinvasive Escherichia coli [EIEC]) from distant areas worldwide, representing all 4 groups and 45 serotypes of Shigella, were screened for set1 by DNA colony hybridization and polymerase chain reaction amplification. set1 was present in all 22 Shigella flexneri 2a strains tested but was rare in isolates of other Shigella serotypes (3.3%, 5/150) and not found in EIEC (0/10). That ShET1 is found almost exclusively in S. flexneri 2a may help explain the epidemiologic predominance of this serotype in the developing world.

Bacterial Toxins↗

PubMed1999

Role and regulation of IL-12 in the in vivo response to staphylococcal enterotoxin B.

Injection of a staphylococcal superantigen (SAg) such as staphylococcal enterotoxin B (SEB) in adult mice results in cytokine production and cell proliferation which can lead to septic shock. The aim of the present work was to identify the cytokines and co-stimulatory molecules regulating the in vivo systemic release of IFN-gamma, a cytokine known to play an important role in the pathophysiology associated with bacterial infections. We demonstrate in this study that (i) in contrast to lipopolysaccharide (LPS), SEB administration induces high levels of the p70, bioactive form, of IL-12; (ii) IL-12 production in response to SEB requires both CD40-dependent signals and IFN-gamma secretion; (iii) the early systemic release of IFN-gamma (3 h post-treatment) in response to SEB is IL-12 independent, while the sustained, late response (6-9 h post-treatment) requires endogenous IL-12 production; (iv) IL-12 produced during the primary SEB response (day 0) is responsible for priming cells in vivo to high IFN-gamma production upon secondary challenge (day 2); (v) the priming effect of IL-12 is TCR unrelated, as SEB-primed animals secrete high levels of IFN-gamma in response to both staphylococcal enterotoxin A and LPS administered 48 h later. The ability of bacterial SAg to induce septic shock and to modulate the immune response to unrelated antigens may therefore be related to their unique capacity to induce systemic IL-12 production in vivo. These observations also help to explain why SEB-primed animals, known to express an anergic phenotype 48 h post-treatment (as judged by defective IL-2 production and proliferation), nevertheless display an increased capacity to secrete the inflammatory cytokine IFN-gamma.

Animals↗

PubMed1994

Identification of two binding sites in staphylococcal enterotoxin B that confer specificity for TCR V beta gene products.

The enterotoxins produced by Staphylococcus aureus are potent mitogens. They stimulate T cells in an oligoclonal fashion that is dependent on the expression of particular variable region gene elements in the beta-chain of the TCR (V beta). The fourth hypervariable loop of the TCR beta-chain is generally regarded as the site of contact for both viral and microbial superantigens. Recently, residues 60 and 61 of staphylococcal enterotoxin B (SEB) have been highlighted as central to the interaction of this toxin with the TCR. We have, therefore, analysed a series of toxins with mutations at these positions to investigate how amino acid substitutions affect the ability of mutant toxins to stimulate both human and mouse T cells. Each of the variant toxins induced proliferation in a murine V beta 8.3 T cell clone, whereas a V beta 8.1 T cell clone only responded to native toxin. A panel of nine human T cell clones expressing six different V beta elements, all of which responded to native SEB, was tested for reactivity to the variant toxins. Only one V beta 19.1+ T cell clone was found to be sensitive to substitution at positions 60 and 61 in a manner analogous to the murine V beta 8.1 T cell clone. Semi-quantitative analysis of the TCR V beta expression of human T cell lines expanded with native and mutant SEB revealed that none of the variant toxins could stimulate T cells that expressed V beta 19.1. Taken together, these results suggest that the interaction of mouse V beta 8.1 and human V beta 19.1 TCRs with SEB differs from other TCRs. Sequence comparisons of the different TCR V beta chains indicated that residues in the second complementarity determining region (CDR2) interact with the 60-61 loop of SEB. Therefore, a minimum of two distinct binding modules confer specificity to the interaction of the TCR with SEB.

Amino Acid Sequence↗

PubMed1995

Selective activation of VH3A10+ rheumatoid factor producing B cells by staphylococcal enterotoxin D.

Staphylococcal enterotoxin D (SED) is a T cell superantigen which selectively targets alpha beta TCRs bearing particular V beta elements. A second function of SED relates to the preferential activation of a B cell subset characterized by a high frequency of rheumatoid factor (RF) producing B cells. To define the molecular basis of the SED-induced B cell repertoire shift, we have analyzed Ig heavy chain genes in B cell clones expanded after SED stimulation and compared them with B cell clones established in the presence of anti-CD3 stimulated helper cells. Gene segments of the VH3 family were most frequently utilized under both stimulation conditions (42% anti-CD3; 47% SED). Sequence analysis of VH3 gene segments demonstrated that the repertoire of VH3 elements in B cell clones from SED driven and anti-CD3 driven cultures were distinct (P = 0.01). RF activity was closely associated with the expression of selected VH3 elements. B cell clones stimulated with SED preferentially expressed VH3A10, whereas VH26 was the gene segment dominantly used in B cell clones expanded with anti-CD3 stimulated helper cells. The usage of JH and DH elements was indistinguishable in SED and anti-CD3 driven B cell clones, suggesting that SED targets VH3+ B cells through a VH-specific mechanism. Comparison of the closely related sequences of the SED responsive VH3A10 and the SED non-responsive VH26 element suggested a role of a sequence polymorphism in the CDR2 reminiscent of B cell reactivity to conventional antigens. In contrast to conventional antigens, SED can induce differentiation of a high frequency of naive B cells. Thus, this staphylococcal enterotoxin combines selective activation of T cells with selective activation of B cells and might be able to direct T cell help to RF producing B cells.

Adult↗

PubMed1994

Oligosaccharides from human milk block binding and activity of the Escherichia coli heat-stable enterotoxin (STa) in T84 intestinal cells.

Enterotoxin-producing Escherichia coli are major causes of pediatric diarrhea in developing countries. The heat-stable enterotoxin of Escherichia coli (STa) causes diarrhea by virtue of its ability to bind to and stimulate intestinal membrane-bound guanylate cyclase, generating cyclic GMP (cGMP). Previous work showed that a fucosylated oligosaccharide fraction of human milk was able to protect suckling mice from the secretory effects of STa, but the mechanism of the protection could not be determined. Oligosaccharide fractions from human milk were tested for their ability to block the biochemical effects of STa in T84 cells, a human colon carcinoma line responsive to the toxin. Total and fucosylated oligosaccharide fractions were found to inhibit STa-stimulated guanylate cyclase activity in T84 cell membranes and cGMP production in intact T84 cells by 60-80%. In addition, the total oligosaccharide fraction and the fucosylated oligosaccharide fraction inhibited 125I-STa binding significantly (17% and 27% inhibition, respectively). These findings demonstrate the protective activity of human milk oligosaccharides against STa in a human-derived cell line and show that the biochemical step blocked by oligosaccharides is STa-mediated stimulation of guanylate cyclase. This represents a novel mechanism by which human milk oligosaccharides protect against diarrhea.

Bacterial Toxins↗

PubMed1985

Protection of suckling mice from heat-stable enterotoxin of Escherichia coli by infant formulas.

Human milk contains factors that protect suckling infants against enteropathogen-induced diarrhea. One nonspecific protective factor found in human milk is a small molecular weight material that protects suckling mice from death due to the heat-stable enterotoxin of Escherichia coli. This study demonstrated that cow's milk and most formulas derived from cow's milk also contain a factor(s) that can protect against heat-stable enterotoxin of E. coli in suckling mice.

Animals↗

PubMed2003

Antithrombin modulates the leukocyte-endothelial cell interaction in the staphylococcal enterotoxin B-challenged mouse.

BACKGROUND: The beneficial effects of antithrombin on endotoxemia are well known. The purpose of this study was to examine the effects of antithrombin in a supertoxin-induced sepsis. METHODS: Mice were injected with staphylococcal enterotoxin B simultaneously with antithrombin. At 1 hour after injection, the mesenteric microcirculation was observed under intravital microscopy. In addition, humoral mediators were measured at the same time. RESULTS: The number of rolling leukocytes on the endothelium was significantly reduced in the treated mice (p < 0.01). The decrease of white blood cell and platelet counts was significantly inhibited in the treated animals (p < 0.01 for both). A comparison of the intercellular adhesion molecule-1 (p < 0.05), soluble tumor necrosis factor-alpha receptor (p < 0.05), and interleukin-6 (p < 0.01) levels showed less increase in the treated mice. CONCLUSION: Antithrombin showed a protective effects on the microcirculation of staphylococcal enterotoxin B-challenged mice by attenuating leukocyte-endothelial cell interaction. Suppression of adhesive molecule expression and cytokine production appears to play roles in this effect.

Animals↗

PubMed1983

Expression of plasmids coding for colonization factor antigen II (CFA/II) and enterotoxin production in Escherichia coli.

Two plasmids transferred from enterotoxigenic Escherichia coli (ETEC) of serotype O6. H16 and biotypes A and C coded for mannose-resistant haemagglutination (MRHA) and production of heat-stable enterotoxin (ST) and heat-labile enterotoxin (LT). Both plasmids were nonautotransferring being mobilized most efficiently by the R plasmid R100-1. They were similar in their genetic properties being incompatible with each other and plasmids of the Inc group FI. The wild-type strains produced the colonization factor antigen II (CFA/II) which was made up of different coli surface antigens (CS). The biotype A strains produced CS1 and CS3 while the biotype C strains produced CS2 and CS3. These three antigens have the ability to cause MRHA. When plasmids coding for MRHA were transferred to K12 strains, the degree of haemagglutination was markedly reduced and only CS3 was produced. When both plasmids were transferred back into biotype A strains, good MRHA was restored and the strains produced CS1 and CS3. In a biotype C strain CS2 and CS3 were formed. The production of the antigens was compared by enzyme-linked immunosorbent assay (ELISA). The strains were also examined by electron microscopy where it was found that CS1 and CS2 were fimbrial antigens while CS3 was not.

Antigens, Bacterial↗

PubMed1989

Cloning in Escherichia coli of the enterotoxin gene from Clostridium perfringens type A.

A 26 bp DNA probe has been constructed with minimal degeneracy to the protein sequence for Clostridium perfringens enterotoxin. The probe has been hybridized against a 6-10 kb chromosomal bank from C. perfringens 8239, prepared as a HindIII partial digest in pHG165. From this survey a clone has been identified containing a 6.8 kb DNA insert with strong hybridization to the probe. Direct plasmid sequencing has identified a translational reading frame within this clone which correlates with the known protein sequence for the type A enterotoxin. DNA sequences 5' to this open reading frame and containing the putative transcriptional control regions show areas of significant homology with regions upstream from the ATG codon of the tetanus toxin gene.

Base Sequence↗

PubMed1989

Staphylococcus aureus bacteriophages mediating the simultaneous lysogenic conversion of beta-lysin, staphylokinase and enterotoxin A: molecular mechanism of triple conversion.

A new group of serotype F bacteriophages of Staphylococcus aureus has been found which mediates the simultaneous triple-lysogenic conversion of enterotoxin A, staphylokinase and beta-lysin. The phages were recovered fro methicillin-resistant strains of S. aureus isolated in Irish hospitals between 1971 and 1988 and from strain PS42-D, which has been used as the propagating strain for the S. aureus typing phage 42D since before 1965. The molecular mechanism of triple conversion mediated by three of these phages was determined by molecular cloning, restriction endonuclease site mapping and hybridization analysis, and compared with the mechanism of beta-lysin and staphylokinase conversion mediated by the serotype F, double-converting phase phi 13. THe genetic determinants mediating expression of enterotoxin A (entA) and staphylokinase (sak) were cloned from the DNA of the triple-converting phage and expression of the cloned determinants detected in Escherichia coli and S. aureus. The entA and sak determinants were closely linked in the phage DNA adjacent to the phage attachment site (attP) in each case and furthermore, the sak determinant of phage phi 13 was also located near its attP. The restriction maps of the entA-, sak- and attP-containing DNA regions of the three triple-converting phages were very similar to each other and to the corresponding sak- and attP- containing DNA region of phage phi 13. Hybridization analysis using a cloned beta-lysin determinant (hlb) and cloned attP-containing DNA fragments as probes demonstrated that beta-lysin conversion mediated by the triple-converting phages and phage phi 13 was caused by insertional inactivation of the chromosomally encoded hlb determinant by orientation-specific integration of phage DNA following lysogenization.

Antimicrobial Cationic Peptides↗

PubMed1992

Expression of the B subunit of Escherichia coli heat-labile enterotoxin in a marine Vibrio and in a mutant that is pleiotropically defective in the secretion of extracellular proteins.

A marine Vibrio (designated Vibrio sp. 60) that is related to Vibrio anguillarum was used as a host for a plasmid that encodes the non-toxic B subunit (EtxB) of Escherichia coli heat-labile enterotoxin. Expression of EtxB in Vibrio sp. 60 resulted in the efficient and selective secretion of the B subunit into the extracellular growth medium. This indicated that Vibrio sp. 60, which does not normally produce cholera-like enterotoxins, nonetheless possesses a secretory machinery that permits these toxins to be translocated across its cytoplasmic and outer membranes. Expression of EtxB in a sec mutant of Vibrio sp. 60 (MVT1192), which had previously been shown to be defective in the secretion of several extracellular proteins, resulted in approximately 95% of the B subunit remaining entrapped within the periplasm of the bacterial cell envelope. This implies that the mutation in MVT1192 defines a locus that determines a common step in the secretion of extracellular proteins, including oligomeric toxins.

Bacterial Proteins↗

PubMed1999

Sequence analysis of three Bacillus cereus loci carrying PIcR-regulated genes encoding degradative enzymes and enterotoxin.

PIcR is a pleiotropic regulator of extracellular virulence factors in the opportunistic human pathogen Bacillus cereus and the entomopathogenic Bacillus thuringiensis, and is induced in cells entering stationary phase. Among the genes regulated by PIcR are: pIcA, encoding phosphatidylinositol-specific phospholipase C (PI-PLC); plc, encoding phosphatidylcholine-preferring phospholipase C (PC-PLC); nhe, encoding the non-haemolytic enterotoxin; hbl, encoding haemolytic enterotoxin BL (HBL); and genes specifying a putative S-layer like surface protein and a putative extracellular RNase. By analysing 37.1 kb of DNA sequence surrounding hbl, plcA and plcR, 28 ORFs were predicted. Three novel genes putatively regulated by PlcR and encoding a neutral protease (NprB), a subtilase family serine protease (Sfp) and a putative cell-wall hydrolase (Cwh) were identified. The corresponding sfp and cwh genes were located in the immediate upstream region of plcA and could both be regulated by a putative PlcR-binding site positioned between the inversely transcribed genes. Similarly, nprB was positioned directly upstream and transcribed in the opposite orientation to plcR. Genes surrounding plcA, plcR and hblCDAB that were lacking an upstream PlcR regulatory sequence did not appear to serve functions apparently related to PlcR and did not exhibit a conserved organization in Bacillus subtilis.

Amino Acid Sequence↗

PubMed1978

Effects of choleragenoid and glucose on the response of dog intestine to escherichia coli enterotoxins.

Culture superantes of Escherichia coli from diarrhoea patients were tested in dog jejunal loops for thermostable (ST) and thermolabile (LT) enterotoxins. Pre-treatment with choleragenoid blocked LT but not ST. Glucose was found to reduce fluid accumulation induced by both types of enterotoxin. The findings confirm and extend previous evidence of similarities between cholera toxin and E. coli LT and differences between it and E. coli ST.

Animals↗

PubMed1979

The ability of cholestyramine resin and other adsorbents to bind Escherichia coli enterotoxins.

Several adsorbent materials were evaluated for their ability to bind Escherichia coli enterotoxins. Cholestyramine, a strong anion-exchange resin, bound the heat-labile and the heat-stable types of enterotoxin and reduced significantly their effects in some animal models. However, its efficacy in the treatment of diarrhoeic piglets appeared to be adversely affected by the presence of milk in the alimentary tract.

Adsorption↗

PubMed1981

Detection of enterotoxins of Aeromonas hydrophila by a suckling-mouse test.

The suckling-mouse assay was reliable for detecting enterotoxigenic strains of Aeromonas hydrophila when standard conditions for growth and toxin testing were used. Enterotoxins were produced by bacteria grown in tryptone soya broth supplemented with yeast extract and aerated by shaking in an environmental incubator or water bath. When culture supernates together with dye were administered intragastrically to mice less than 6 days old, the presence of enterotoxin was assessed on the basis of a scoring system that incorporated the ratio intestinal weight: remaining body weight, and production of diarrhoea. This method should facilitate the detection of enterotoxigenic strains of Aeromonas in epidemiological studies.

Aeromonas↗

PubMed1986

Enterotoxin production by Salmonella typhimurium strains of different virulence.

Six strains of Salmonella typhimurium (TML, W118, LT7, SL1027, M206 and Thax-1) of known virulence and ability to induce fluid secretion when inoculated into the rabbit ileum were examined for enterotoxin production. Enterotoxic activity, assayed in the rabbit ileal-loop test, was detected in polymyxin-B extracts from all strains (with the possible exception of Thax-1) cultured for 6 h in casamino acid-yeast extract medium. The extracts were inactive in tissue-culture assays with CHO, Y-1 adrenal and Vero cells, and in the infant mouse assay for enterotoxin. There was no correlation between enterotoxigenicity in vitro and the ability of whole organisms to induce fluid secretion in vivo. The significance of these results in relation to salmonellosis is discussed.

Animals↗