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PubMed1984

Immunological properties of porcine enterotoxigenic Escherichia coli heat-stable (ST) enterotoxins.

Cross-linking semipurified and purified heat-stable enterotoxin (2023 ST) to carrier proteins with glutaraldehyde pigs and rabbits were immunized. With ST antisera thus raised, a relatively simple, two-step method for isolation of ST is described. The method involved immunoadsorbent column chromatography procedure, and elution of the retained material with 6 M urea at pH 3.0 yielded purified ST with enterotoxin activity, controlled in suckling mouse test. ST purity was checked with a special staining technique in PAGE, anionic-exchange chromatography and immunodiffusion.

Animals↗
PubMed1995

Intestinal immune response induced in mice by staphylococcal enterotoxin B.

To investigate the induction of intestinal immunity to staphylococcal enterotoxins (SE) we have chosen the mouse as an experimental model. Since this species is devoid of emetic mechanism, SE can be administered orally without any loss. Mice were treated orally and/or parenterally with staphylococcal enterotoxin B (SEB). The anti-SEB response, either in serum or in the supernatant of in vitro cultured intestinal fragments was determined by enzyme immunoassay (EIA). The results showed that orally given SEB induced specific antibodies both in serum and intestinal secretions. Compared to oral route alone, parenteral followed by oral administration of SEB induced a higher intestinal response with IgA as predominant isotype. Although these results cannot directly be extrapolated to humans or animals with emetic reaction to SE, they do show the implication of intestinal immune system in response to this group of toxins.

Animals↗
PubMed1991

Stimulation of CD2-negative T cells by staphylococcal enterotoxin superantigens.

A minor fraction of CD3+ T cells lacks expression of the CD2 antigen, which is the target for an "alternative" T cell activation pathway. CD2-CD3+ T cells can be stimulated by anti-CD3 or anti-T cell receptor (TCR) antibodies, indicating that the CD3/TCR signal transduction pathway functions in the absence of cell surface CD2. In the present study we have analyzed whether CD2-CD3+ T cells also respond to antigen stimulation. We show here that cloned CD2-negative T cells expressing the alpha/beta TCR are activated by one or several staphylococcal enterotoxin "superantigens". Activation of CD2-CD3+ T cell clones by staphylococcal enterotoxins resulted in IL-2 production and/or proliferative activity, and was dependent on the presence of HLA class II-bearing feeder cells. These data demonstrate that T cells can recognize (and respond to) antigen in the absence of a functional CD2 molecule.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1994

Cell adhesion molecules are co-receptors for staphylococcal enterotoxin B-induced T-cell activation and cytokine production.

Enterotoxins produced by Staphylococcus aureus are potent mitogens for human T cells and cause lethal toxic shock. These superantigens bind to major histocompatibility complex class II on antigen-presenting cells outside the conventional peptide-binding groove and stimulate T cells expressing certain T-cell receptor V beta gene products. We investigated other cell-surface molecules on human peripheral blood mononuclear cells that can mediate staphylococcal enterotoxin B (SEB)-induced T-cell proliferation and cytokine production. SEB-induced proliferation of T cells was inhibited by monoclonal antibodies to CD2, CD11a, CD18, CD28, CD44, CD58 and ICAM-1. Anti-ICAM-1 also blocked the production of pro-inflammatory mediators, TNF alpha and IFN gamma by SEB-stimulated T cells. These data suggest that the surface molecules, CD11a:CD18/ICAM-1, CD2/CD58, CD28 and CD44, are all important co-receptors for T-cell activation by superantigens. Thus, like conventional antigens, multiple stimulatory signals from the interactions of these receptors are required for superantigen-induced immune responses. Reducing toxic mediators such as TNF alpha and IFN gamma by anti-ICAM antibodies in SEB-induced T-cell responses may be a useful therapeutic strategy to circumvent SEB toxicity and pathogenesis.

Antibodies, Monoclonal↗
PubMed1982

Effects of temperature, pH and detergents on the molecular conformation of the enterotoxin of Clostridium perfringens.

The effects of temperature, pH and sodium dodecyl sulfate on the conformation of the enterotoxin from Clostridium perfringens type A were followed by circular dichroism in both the peptide and aromatic regions. At near-physiological conditions (35 degrees C, pH 6.7) the enterotoxin exhibited a conformation consisting of approximately 60% pleated sheet, 40% non-periodic, and essentially no helix. The peptide region was relatively stable at temperatures up to 55 degrees C and at pH values ranging from 4-10. The aromatic region demonstrated profound, time-dependent changes at 55 degrees C. At temperatures greater than 55 degrees C, extremes of pH, and in the presence of SDS, the spectra in both regions showed major structural reorganization; in most cases a gain in helical content at the expense of sheet structure was observed. The conformational properties of the protein are very similar to those observed for the lectins, a group of carbohydrate-binding proteins.

Circular Dichroism↗
PubMed1988

The effect of heat-stable Escherichia coli enterotoxin, theophylline and forskolin on cyclic nucleotide levels and mucosal surface (acid microclimate) pH in rat proximal jejunum in vivo.

The normally acidic mucosal surface pH of 6.24 +/- 0.02(30) in rat proximal jejunum in vivo is effectively neutralised by 30 min exposure to heat-stable Escherichia coli (STa) enterotoxin (14 micrograms/ml) to 6.80 +/- 0.07 (n = 5) or to a forskolin/theophylline combination (1 mM:20 mM) to 7.10 +/- 0.07(7) while perfusion with Krebs-phosphate buffer alone without glucose left the mucosal surface pH unchanged at a pH of 6.21 +/- 0.02(9). Forskolin alone had no effect, and 20 mM theophylline moderately elevated the surface pH to 6.52 +/- 0.03(5). Theophylline, forskolin and their combination all elevated cAMP levels per mg tissue DNA above control values while STa enterotoxin was without effect. In contrast, all agents elevated cGMP levels per mg tissue DNA above control levels. These findings indicate that surface pH is only moderately affected by changes in cAMP levels and is affected to a much greater extent by altered cGMP levels.

Animals↗
PubMed1995

Evidence for stimulation of the inositol triphosphate-Ca2+ signalling system in rat enterocytes by heat stable enterotoxin of Escherichia coli.

In Escherichia coli heat stable enterotoxin (STa)-treated rat enterocytes, the rise of inositol triphosphate (IP3) preceded the rise of [Ca2+]i. Chelation of extracellular Ca2+ with EGTA and suspension of cells in Ca2+ free buffer both demonstrated the enterotoxin-induced initial rise of [Ca2+]i with a concomitant loss of sustained phase. Furthermore, pretreatment of cells with dantrolene resulted in a decrease of the early response of [Ca2+]i, indicating the initial effect of the rise of [Ca2+]i was mostly due to its mobilization from some IP3-sensitive intracellular stores.

Animals↗
PubMed1988

The detection of enterotoxin and toxic shock syndrome toxin-1 production by strains of Staphylococcus aureus with commercial RPLA kits.

Two reversed passive latex agglutination kits (SET-RPLA and TST-RPLA) were used to detect enterotoxin and toxic shock syndrome toxin-1 (TSST-1) production by 334 strains of Staphylococcus aureus isolated from clinical sources and from outbreaks of food poisoning. The results were compared to those obtained with the traditional gel diffusion method. All strains positive by gel diffusion were also positive by RPLA. Seventeen strains produced low levels of TSST-1 or enterotoxins C or D which were only detected by the RPLA method. Some non-specific reactions were obtained with the SET-RPLA kit, but not with the TST-RPLA kit.

Bacterial Toxins↗
PubMed1989

ELISA with enzyme amplification for sensitive detection of staphylococcal enterotoxins in food.

A highly sensitive amplified ELISA in microtitre plates for the detection of staphylococcal enterotoxins compared favourably with a commercially available kit. The amplified ELISA demonstrated a reduced effect of the food sample matrix and an ease of handling. Using the amplified ELISA, the influence of different parameters (pH, time, temperature, re-extraction, concentration procedure) on the recovery efficiency and assay reliability was tested on foods implicated in food poisoning outbreaks as well as on spiked foods containing low levels of enterotoxins.

Enterotoxins↗
PubMed1989

Detection of staphylococcal enterotoxins in dairy products by the reversed passive latex agglutination (SET-RPLA) kit.

The SET-RPLA is a commercially available kit for the detection of staphyloccal enterotoxins in foods. Previous reports have shown that non-specific reactions occur on use of the kit with cheeses and thereby restrict its use. In this study a variety of dairy products were tested and non-specific reactions were found to be associated with those products rennetted during manufacture. These reactions can be obviated by addition of 10 mM sodium hexametaphosphate to the diluent provided in the kit, without affecting the ability to detect staphyloccal enterotoxins in dairy products. The sensitivity of the SET-RPLA was demonstrated to be 0.25 ng/ml.

Animals↗
PubMed1991

Comparison of four kits for the detection of staphylococcal enterotoxin in foods from outbreaks of food poisoning.

Four commercial kits, three based on sandwich ELISA techniques and one on latex agglutination were compared for the detection of staphylococcal enterotoxins in foods from outbreaks of food poisoning. Enterotoxin was detected in 14 of 18 foods with the Swiss SET-EIA and in 9 or 10 with the Unipath SET-RPLA and two ELISAs from Transia. The advantages and disadvantages of the four methods are discussed.

Animals↗
PubMed1996

A collaborative study on the detection of staphylococcal enterotoxins in foods by an enzyme immunoassay kit (RIDASCREEN).

The RIDASCREEN SET kit (R-Biopharm GmbH, Darmstadt, Germany), a commercial staphylococcal enterotoxin (SE) immunoassay kit, utilizes monovalent capture antibodies against SE types A to E (SEA to SEE); therefore, it simultaneously detects and identifies the enterotoxin types. A collaborative study was conducted to ascertain whether the specificity, sensitivity, repeatability and reproducibility of the kits would meet food safety criteria. Twelve Canadian laboratories participated in this study to analyze various foods to which 1.0 to 2.0 ng of SE/g had been added and negative control samples. The results indicate that the sensitivity and specificity of the kit were excellent; all collaborators were able to detect the minimum toxin levels of 1.0 ng SEA/g in ham and cheese, 1.0 ng SEB/g in salami and turkey, and 2.0 ng SED/g in other samples without any false-negative results. With regard to negative control samples, all analysts obtained correct results except for one analyst who recorded weak false-positive results with several foods detecting SEC or SEA. The overall rate of false-positive results was 0.7% for 600 triplicate assays. In addition, it was confirmed that the RIDASCREEN kit did not yield false-positive results with mussels in contrast to some other EIA kits. Overall repeatability and reproducibility of the kit were in the range of 11.69-42.57% and 17.25-68.05%, respectively.

Animals↗
PubMed1988

Adjuvant activity of Escherichia coli heat-labile enterotoxin and effect on the induction of oral tolerance in mice to unrelated protein antigens.

The ability of Escherichia coli heat-labile enterotoxin (LT) to influence the induction and maintenance of tolerance was examined in animals primed orally with a soluble protein antigen, ovalbumin (OVA), or in animals primed orally with two unrelated protein antigens administered simultaneously, OVA and bovine serum albumin (BSA). LT is immunologically and structurally related to the cholera enterotoxin (CT), which has been shown to be capable of abrogating oral tolerance to protein antigens when delivered simultaneously with the antigens. In this study, simultaneous administration of LT with OVA was shown to prevent the induction of tolerance to OVA and to increase the serum anti-OVA IgG response 30- to 90-fold over OVA-primed and PBS-primed animals, respectively. This effect was determined to be a function of the enzymatically active A subunit of the toxin since the B (binding) subunit alone was unable to influence tolerance induction. Animals fed LT with OVA after the initial OVA prime developed a significantly lower serum IgG and mucosal IgA anti-OVA response than those fed LT with OVA in the initial immunization, indicating that prior exposure to the antigen reduces the effectiveness of LT to influence tolerance and its ability to act as an adjuvant. LT was not able to abrogate tolerance once it had been established. Serum IgG and mucosal IgA responses in animals receiving LT on only a single occasion, that being upon first exposure to antigen, were equivalent to responses after three OVA/LT primes, indicating that commitment to responsiveness occurs early and upon first exposure to antigen.(ABSTRACT TRUNCATED AT 250 WORDS)

Adjuvants, Immunologic↗
PubMed1987

Studies on the mechanism of Escherichia coli heat-stable enterotoxin-induced diarrhoea in mice.

The unidirectional fluxes of Na+, Cl- and Ca2+ and activities of calmodulin in the intestinal microvillar core were studied in Escherichia coli heat-stable enterotoxin-treated mice. There was net secretion of Na+ and Cl- in toxin-treated animals, while in control animals there was net absorption of these ions. In both control and experimental animals, there was net absorption of Ca2+; however, the absorption was significantly higher (P less than 0.01) in experimental animals when compared to controls. In the presence of Ca2+-ionophore, there was a net secretion of Na+ and Cl- in controls, while the Ca2+-ionophore could not cause any change in the fluxes of these ions in experimental animals. The activity of calmodulin was significantly higher (P less than 0.01) in experimental animals. Verapamil, a calcium channel blocker, and trifluoperazine, a calmodulin inhibitor, reversed the effects of Ca2+-ionophore and heat-stable enterotoxin. These studies demonstrate that the toxin acts through Ca2+-calmodulin, and secretion of Na+ and Cl- in experimental animals is due to an increase in calcium absorption and an increase in calmodulin activity in the intestinal microvillar core.

Animals↗
PubMed1989

Profiles of enterotoxin and cytotoxin production in Campylobacter jejuni and C. coli.

Enterotoxin and cytotoxin production of 10 strains of Campylobacter spp. were examined by ELISA and HeLa cells assay, respectively. Both toxins were produced in high concentrations by strains freshly isolated from patients. The maximum enterotoxin activity was found to be at 24 h after incubation, at which time cell growth reached the stationary phase. On the other hand, production of cytotoxin increased after the logarithmic phase of the growth.

Campylobacter↗
PubMed1990

Comparison of coligenoid formation by B subunits of porcine and human Escherichia coli heat-labile enterotoxins.

A hybrid B subunit (coligenoid) of heat-labile enterotoxin could not be made from human heat-labile enterotoxin B subunit(LTh-B) and porcine LTp-B subunit(LTp-B). LTp-B monomer was able to form coligenoid by reassociation with homologous LTp-B monomer, but not with heterogeneous LTh-B monomer and vice versa. The dissociation of both coligenoids into monomers by SDS treatment occurred in a time-dependent manner, but the dissociation of LTh-B colligenoid was faster than that of LTp-B coligenoid. The association of LTp-B monomer is tighter than that of LTh-B monomer. The pI values of LTp-B coligenoid, LTp-B monomer and denatured LTp-B monomer were similar at 9.6-9.8, while the pI values of LTh-B coligenoid, LTh-B monomer and denatured LTh-B monomer were determined as 5.6-5.8, 9.2-9.6 and 9.2-9.6, respectively. All the ionic amino acids of LTp-B exist on the coligenoid surface. The difference in pI values between LTh-B coligenoid and LTh-B monomer suggests that some basic amino acids are located within the LTh-B coligenoid complex, but are exposed in the LTh-B monomer. These data suggest that the 4 amino acid substitutions between LTh-B and LTp-B result in a three dimensional structure difference and a less stable formation of LTh-B coligenoid compared to LTp-B coligenoid.

Animals↗
PubMed1991

Detection of heat-stable enterotoxin in a cholera toxin gene-positive strain of Vibrio cholerae O1.

DNA colony hybridization with a polynucleotide clonal DNA probe for heat-stable enterotoxin of Vibrio cholerae non-O1 (NAG-ST) was used to screen 197 isolates of V. cholerae O1. Under stringent hybridizing and washing conditions, one strain (GP156) reacted with the probe. The concentrated supernatant from V. cholerae O1 GP156, heated at 100 degrees C for 5 min, elicited fluid accumulation in the suckling mice and that could be completely neutralized by an anti-NAG-ST monoclonal antibody (mAb2F). The preparation from V. cholerae O1 GP156 also inhibited the binding of mAb2F to NAG-ST in a competitive ELISA. V. cholerae O1 GP156 was confirmed to possess a gene encoding cholera toxin (CT). These results indicate that a heat-stable enterotoxin is produced by certain strains of CT-producing V. cholerae O1.

Animals↗