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PubMed1978

Stimulation of cyclic AMP secretion in Vero cells by enterotoxins of Escherichia coli and Vibrio cholerae.

The morphological response of Vero cells to Escherichia coli heat-labile enterotoxin was similar to that of cholera toxin and was accompanied by increases in the intracellular level of cyclic AMP. The effects of both enterotoxins were enhanced by the presence of phosphodiesterase inhibitor and inhibited by heat or specific antisera. Accumulation of cyclic AMP preceded the morphological response.

1-Methyl-3-isobutylxanthine↗
PubMed1978

Purification of heat-labile enterotoxin from four Escherichia coli strains by affinity immunoadsorbent: evidence for similar subunit structure.

A single-step method for the purification of heat-labile enterotoxin of Escherichia coli is described. The method involves an affinity immunoadsorbent made with antiserum to cholera toxin. Crude toxin preparations of three human and one porcine enterotoxinogenic strains of E. coli were purified on this immunoadsorbent, and the elution products suggest that the toxin molecule is composed of subunits. One kind of subunit shared by these four strains showed similar mobility of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, close antigenic relationship, and an antigen in common with cholera enterotoxin.

Antigens, Bacterial↗
PubMed1979

Nutritional requirements for synthesis of heat-labile enterotoxin by enterotoxigenic strains of Escherichia coli.

Optimal growth conditions have been established for production of heat-labile enterotoxin (LT) by both porcine and human strains of enterotoxigenic (ENT(+)) Escherichia coli. There were no unusual growth factor requirements, and some strains produced fairly high levels of LT in a basal salts medium containing 0.5% glucose if the pH was carefully controlled. Several amino acids markedly stimulated LT synthesis when added to the basal salts-glucose medium. Methionine and lysine were the most stimulatory for both human and porcine strains. Either aspartic acid or glutamic acid further enhanced LT synthesis in the presence of methionine and lysine, with aspartic acid being more stimulatory for porcine strains and glutamic acid more stimulatory for human strains. There were no apparent vitamin requirements and no unusual cations needed for toxin synthesis except that Fe(3+) was slightly stimulatory for porcine strains. The stimulation by Fe(3+) was observed only in the presence of the three amino acids, suggesting that the effect was indirect rather than on toxin synthesis. The carbon source also influenced the yield of LT. Glucose supported maximal synthesis, but other carbon sources which exhibit a high degree of catabolite repression also supported high levels of synthesis. Little or no LT was released below pH 7.0; therefore, because the pH drops during growth from 7.5 to 6.8, even in highly buffered media, it was necessary to adjust the pH to 8.0 to effect complete release of cell-associated toxin. The defined medium containing three amino acids reduced the amount of UV-absorbing material in culture supernatants about fivefold and increased LT activity for various strains from two- to fivefold over a complex Casamino Acids-yeast extract medium. Conditions found to be optimal for synthesis of LT were inhibitory for the heat-stable enterotoxin.

Amino Acids↗
PubMed1979

Factors affecting release of heat-labile enterotoxin by enterotoxigenic Escherichia coli.

Various conditions affecting the release of heat-labile enterotoxin (LT) by enterotoxigenic Escherichia coli have been examined. The pH of a defined medium containing three amino acids, M-9 salts, and 0.5% glucose decreased to less than 7.0 in early log phase of growth, and no extracellular LT was detected. Adjustment of the pH at 8 h from 6.0 to 8.0 resulted in a concomitant increase in LT activity in culture supernatants. The release of cell-associated LT was significantly reduced by preincubation with protease inhibitors and increased by preincubation with trypsin. Cell-associated LT was not released by pH adjustment of cells grown at 21 degrees C; however, polymyxin B treatment released a toxin species active in only the pigeon erythrocyte lysate (PEL) assay system. As the growth temperature was increased, polymyxin B released toxin species which exhibited both PEL and Y-1 adrenal tumor cell activity. Polymyxin B extracts of enterotoxigenic E. coli in early log phase grown at 37 degrees C possessed only PEL activity, whereas extracts from cells in late-log and stationary phases had biological activity in both assay systems. Also, LT released by pH adjustment from mid-log to stationary phase was active in both PEL and Y-1 adrenal tumor cell assays. Gel electrophoresis of polymyxin B extracts revealed at least three molecular weight species active in either the PEL (22,000 daltons and 30,000 daltons) or both the PEL and the Y-1 adrenal tumor cell assay (72,000 daltons), depending on the growth temperature. These observations may help to explain the chemical and biological heterogeneity of most LT preparations and facilitate purification of LT by increasing the yield of enterotoxin.

Bacterial Toxins↗
PubMed1979

Purification and chemical characterization of the heat-labile enterotoxin produced by enterotoxigenic Escherichia coli.

Heat-labile enterotoxin (LT) produced by a human strain of enterotoxigenic Escherichia coli (286C(2)) was purified to homogeneity from pH extracts of fermentor-grown cells by ultrafiltration, (NH(4))(2)SO(4) fractionation, hydrophobic chromatography on norleucine-Sepharose 4B, hydroxylapatite chromatography, and Bio-Gel P-150 filtration. Purified LT preparations exhibited biological activity comparable to that of cholera toxin in four bioassays specific for the two enterotoxins (Y-1 adrenal tumor cells, Chinese hamster ovary cells, pigeon erythrocyte lysates, and skin permeability test). The overall yield of LT protein was 20%, which represented a 500-fold purification over pH extracts. A native molecular weight of 73,000 was determined by gel electrophoresis. The toxin dissociated upon treatment with sodium dodecyl sulfate, pH 7.0, into two components with molecular weights of 44,000 and 30,000. Purified LT preparations were remarkably stable over a wide range of storage conditions, temperatures, and pH's. The biological activity was increased by incubation with trypsin and completely destroyed by pronase and proteinase K, whereas deoxyribonuclease I, ribonuclease, and phospholipase D had no effect. The amino acid composition of purified LT was quite different from that of cholera toxin. Neither carbohydrate nor lipopolysaccharide was present in purified preparations. The purification scheme appeared applicable to LT produced by other human and porcine enterotoxigenic strains, but reflected the amount of LT produced by each strain. These data show that LT and cholera toxin share many common chemical and physical properties, but must be purified by different techniques.

Amino Acid Sequence↗
PubMed1980

Influence of route of administration on immediate and extended protection in rats immunized with Escherichia coli heart-labile enterotoxin.

The effect of route of administration, dosage, and number of boosts employed during immunization with the polymyxin-release form of Escherichia coli heat-labile (LT) enterotoxin on the degree and duration of protection afforded was evaluated in rats which were challenged by the ligated loop technique. Increasing the boosting dosage by fivefold from 50 to 250 mug resulted in a marked increase in protection against challenge with toxin in rats immunized either just by the parenteral route (i.p./i.p.) or by a parenteral prime, followed by peroral boosts (i.p./p.o.) in rats pretreated with cimetidine to ablate gastric secretions; such was not the case, however, even with a 50-fold increase in dosage in rats immunized just by the peroral route (p.o./p.o.). Four weekly peroral boosts were required to achieve the strongest degree of protection. Increasing the boosting dosage also increased the degree of protection against challenge with viable LT(+)/ST(-) and LT(+)/ST(+) strains (ST indicates heat-stable enterotoxin) in rats immunized by the i.p./p.o., but not by the i.p./i.p., route; no protection was evident against an LT(-)/ST(+) strain. Protection was lost within 3 weeks after immunization in rats immunized by the i.p./i.p. route. In contrast, protection was extended over the 3-month observation period in those immunized by the i.p./p.o. route; the degree of protection was enhanced in rats which received an additional boost at 2 months. These observations establish the fact that immunization with LT is similar to that with cholera toxin in that arousal of the local immune intestinal response by means of peroral immunization provides maximal extended protection.

Animals↗
PubMed1980

Protective effect of immunization with heat-labile enterotoxin in gnotobiotic rats monocontaminated with enterotoxigenic Escherichia coli.

The protective effect of active immunization with a purified preparation of the polymyxin-release form of Escherichia coli heat-labile enterotoxin (LT), administered using a parenteral prime and peroral boosts given after ablation of gastric secretion by means of cimetidine, was assessed in gnotobiotic rats which were challenged by monocontamination with enterotoxigenic strains of E. coli. Water transport was evaluated by the in vivo marker perfusion technique at weekly intervals over a 3-week period after contamination. Water transport in unimmunized control rats was consistently in absorption in those contaminated by a nontoxigenic strain, in secretion during only week 2 in those contaminated by an LT(+)/- strain, in secretion during weeks 2 and 3 in those contaminated by an LT(+)/ST(+) (heat-stable enterotoxin) strain, and consistently in absorption in those contaminated by an -/ST(+) strain. Rats immunized with a booster dosage of 250 mug had a significant increase (P < 0.001) in net water absorption as compared to unimmunized rats, with values in the borderline range of absorption, when challenged with either the LT(+)/- or LT(+)/ST(+) strains. Rats immunized with a 10-fold-higher boosting dosage had a significant increase (P < 0.001) in net water absorption as compared to those boosted at the lower dosage; water absorption was within the normal range. There was no difference between the ileal bacterial counts of unimmunized and immunized rats challenged by the various strains. These observations indicate that this immunization program provides complete protection in an animal model against challenge by intestinal contamination with enterotoxigenic strains of E. coli which produce LT, either alone or in combination with ST.

Animals↗
PubMed1981

Production of heat-labile or heat-stable enterotoxins by strains of Escherichia coli belonging to serogroups O44, O114, and O128.

Strains of Escherichia coli which belong to enteropathogenic serogroups usually fail to produce heat-labile or heat-stable enterotoxins. However, 1 of 34 strains of E. coli O44, 9 of 45 strains of E. coli O114, and 18 of 82 strains of E. coli O128 produced heat-labile or heat-stable enterotoxins. Most enterotoxigenic isolates were from tropical or developing countries; all three enterotoxigenic strains isolated in Britain were from patients returned from abroad. Enterotoxigenic strains were of many different flagellar types. Certain enterotoxigenic strains of E. coli O114 and O128 possessed colonization factor antigen I.

Antigens, Bacterial↗
PubMed1981

Development of a radioimmunoassay for Escherichia coli heat-stable enterotoxin: comparison with the suckling mouse bioassay.

Escherichia coli strains which produce heat-stable enterotoxin (ST) are usually identified by demonstrating the production of ST. At present, ST can be detected only by bioassay methods. Recently, we purified E. coli ST, which enabled us to develop a radioimmunoassay for ST. Radioiodination of ST was performed by the lactoperoxidase method, which resulted in a high specific activity and retained the biological activity of St. Anti-ST antisera were raised in goats by injecting the goats with pure ST coupled to bovine immunoglobin G. Antibody titers ranged from 1:8,000 to 1:40,000. Using these reagents, we examined assay conditions thoroughly and found that a 14- to 18-h incubation at 4 degrees C in sodium acetate buffer with an ionic strength of 120 mM (pH 6.2) gave maximal sensitivity and reproducibility. Free ST was separated from antibody-bound ST by dextran-coated charcoal. This radioimmunoassay accurately and reproducibly measured ST in the range from 50 to 500 pg of ST per tube and could quantitate ST accurately in complex bacteriological media. This assay was specific for STa, measured human and porcine STa equally well, and did not cross-react with STb, with several other enterotoxins, or with various gastrointestinal peptides. Intact disulfide bridges in the ST molecule were required for immunoreactive activity.

Animals↗
PubMed1981

Stimulation of Clostridium perfringens enterotoxin formation by caffeine and theobromine.

In the presence of 100 micrograms of caffeine per ml or 200 micrograms of theobromine per ml, sporulation of Clostridium perfringens NCTC 8679 rose from less than 1 to 80 or 85%. Enterotoxin concentration increased from undetectable levels to 450 micrograms/mg of cell extract protein. Heat-resistant spore levels increased from less than 1,000 to between 1 X 10(7) and 2 X 10(7)/ml. These effects were partially reversible by the addition of adenosine or thymidine. In the case of NCTC 8238, caffeine and theobromine caused a three- to fourfold increase in the percentages of cells possessing refractile spores and a similar increase in enterotoxin concentration. Heat-resistant spore levels, however, were unaffected. Inosine was ineffective in promoting sporulation in NCTC 8679.

Caffeine↗
PubMed1981

Isolation of special antibodies which react only with homologous enterotoxins from Vibrio cholerae and Enterotoxigenic Escherichia coli.

Cholera enterotoxin (CT) and heat-labile enterotoxin (LT) produced by enterotoxigenic Escherichia coli share a common antigenic determinant. In addition, CT and LT each have a unique antigenic determinant. Antisera were prepared by immunoaffinity chromatography against these unique antigenic determinants, that is, antiserum that reacted with CT but not with LT and antiserum that reacted with LT but not with CT. Antiserum against the common antigenic determinant to CT and LT was also prepared by immunoaffinity chromatography. The specificities of these antisera were demonstrated by Ouchterlony double-gel diffusion tests and by neutralization of the activities of CT and LT to cause morphological changes in Chinese hamster ovary cells.

Animals↗
PubMed1982

Potentiating effect of bile on enterotoxin-induced diarrhea.

The influence of bile acids on adenosine 3',5'-phosphate-induced intestinal secretion was studied in mice. Bile flow was stopped by ligation of the common bile duct, and secretion was induced in ligated loops of the small intestine. The decrease of bile led to inhibition of hypersecretion after challenge with heat-labile enterotoxins from Vibrio cholerae and Escherichia coli, as well as with prostaglandin E1. In contrast, the fluid response induced by dibutyryl-adenosine 3',5'-phosphate was unaffected by intestinal bile. Injection of bile or bile acids into intestinal loops before cholera toxin challenge restored the toxin-induced secretion in the bile-depleted intestine. At the subcellular level the decrease of intestinal bile led to inhibition of cholera toxin-activated adenylate cyclase, whereas the bile concentration did not influence the binding of 125I-labeled toxin to the intestinal epithelial cells. The results suggest that intestinal bile interacts with adenylate cyclase in the induction of fluid secretion by enterotoxins and prostaglandin E1.

Adenylyl Cyclases↗
PubMed1982

Molecular heterogeneity of heat-labile enterotoxins from human and porcine enterotoxigenic Escherichia coli.

The heat-labile enterotoxins produced by human enterotoxigenic Escherichia coli (LTh) and porcine enterotoxigenic E. coli (LTp) were purified to homogeneity, and their molecular properties were compared with those of purified cholera enterotoxin (CT). On polyacrylamide gel disk electrophoresis without sodium dodecyl sulfate, LTh, LTp, and CT differed in mobility, suggesting differences in their ionic charges. The pI values of LTh, LTp, and CT were 7.50, 8.10, and 6.80, respectively. On sodium dodecyl sulfate-polyacrylamide gel slab electrophoresis, the B subunit and A1 and A2 fragments of LTh, LTp, and CT differed in mobility, suggesting that they differed in molecular size. Their molecular sizes seemed to decrease in the following order: B subunit, LTh greater than LTp congruent to CT; A1 fragment, LTp greater than LTh congruent to CT; A2 fragment, LTh congruent to CT greater than LTp. Amino acid compositions of LTh, LTp, and CT were also compared.

Amino Acids↗
PubMed1983

Properties of synthetically produced Escherichia coli heat-stable enterotoxin.

The properties of a synthetically produced peptide composed of the same primary structure of 18 amino acids described for human Escherichia coli heat-stable enterotoxin were compared with those of purified heat-stable toxin obtained by bacterial growth. The dosage required to evoke fluid secretion in the suckling mouse and rat ligated ileal loop assays was the same for both toxins. The antigenicity of the two toxins was similar when assayed by enzyme-linked immunosorbent assay with hyperimmune antiserum to either toxin. The secretory effect of the two toxins in the suckling mouse assay was seroneutralized by the same dilutions of hyperimmune antiserum to either toxin. Immunization of rats with the synthetic toxin coupled to a large-molecular-weight carrier raised serum and mucosal antitoxin responses which provided protection against challenge with either the synthetic or biological toxin as well as with viable heat-stable enterotoxin-in-producing organisms. These observations indicate that synthetically produced heat-stable toxin has the same properties as the toxin derived by bacterial culture. The availability of the more readily made synthetic form of heat-stable toxin should facilitate the production of a vaccine based on cross-linking this toxin with either the heat-labile toxin or its nontoxic B subunit.

Animals↗
PubMed1983

Peroral immunization of rats with Escherichia coli heat-labile enterotoxin delivered by microspheres.

The antigenicity of the Escherichia coli heat-labile enterotoxin was not protected against the adverse effect of gastric acidity when the toxin was given together with bicarbonate for peroral immunization to rats, but immunization with the heat-labile enterotoxin encapsulated in pH-dependent microspheres aroused the same strong degree of serum and mucosal antitoxin responses and of protection against challenge as was achieved by peroral immunization after ablation of gastric secretions by pretreatment with cimetidine.

Administration, Oral↗
PubMed1971

Production of extracellular enzymes and enterotoxins A, B, and C by Staphylococcus aureus.

Eighty-seven strains of Staphylococcus aureus were examined for their ability to produce enterotoxins A, B, and C, deoxyribonuclease, lysozyme, proteinase, lipase, and alpha-, beta-, and delta-hemolysins. Enterotoxigenic strains showed a significant tendency to be high lipase producers, but none of the other enzymes formed were correlated with the ability of the staphylococci to produce enterotoxins A, B, or C. The conversion of ent(-) to ent(+) strains by lysogenization did not affect significantly the ability of the strains to produce any of the above extracellular enzymes. The formation of enzymes such as deoxyribonuclease and lysozyme by staphylococci is not therefore an indication, necessarily, of their potential enterotoxigenicity.

Bacterial Proteins↗