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PubMed2001

Staphylococcus aureus agr genotypes with enterotoxin production capabilities can resist neutrophil bactericidal activity.

Staphylococcus aureus pathogenicity is mainly due to the production of a number of secreted and cell surface-associated proteins under the regulation of the agr gene. A region of the agr gene was used to subgroup S. aureus strains according to restriction fragment length polymorphisms. Additionally, strains were subtyped according to the coagulase gene in order to strengthen discriminatory power. Virulence capabilities of agr genotype subgroups were evaluated using an in vitro neutrophil bactericidal assay, which showed that prevalent genotypes were significantly better at evading this primary host defense. Multiplex PCR was then used to detect enterotoxin genes among the genotype subgroups in order to determine possible virulence candidates that enable strains to combat neutrophil killing. The prevalent genotype strains were found to possess higher production capabilities for enterotoxin A than did low-prevalence strains. The significance of enterotoxin A production capabilities in affecting pathogenicity of S. aureus strains was evaluated and found to have a profound effect on neutrophil killing abilities. The use of a large epidemiological database as a tool for subgrouping strains with varying degrees of pathogenicity has allowed the identification of relevant and previously undefined virulence factors that affect a pathogen's capability to overcome host immune defenses.

Animals↗

PubMed2001

Characterization of receptor-mediated signal transduction by Escherichia coli type IIa heat-labile enterotoxin in the polarized human intestinal cell line T84.

Escherichia coli type IIa heat-labile enterotoxin (LTIIa) binds in vitro with highest affinity to ganglioside GD1b. It also binds in vitro with lower affinity to several other oligosialogangliosides and to ganglioside GM1, the functional receptor for cholera toxin (CT). In the present study, we characterized receptor-mediated signal transduction by LTIIa in the cultured T84 cell model of human intestinal epithelium. Wild-type LTIIa bound tightly to the apical surface of polarized T84 cell monolayers and elicited a Cl(-) secretory response. LTIIa activity, unlike CT activity, was not blocked by the B subunit of CT. Furthermore, an LTIIa variant with a T14I substitution in its B subunit, which binds in vitro to ganglioside GM1 but not to ganglioside GD1b, was unable to bind to intact T84 cells and did not elicit a Cl(-) secretory response. These findings show that ganglioside GM1 on T84 cells is not a functional receptor for LTIIa. The LTIIa receptor on T84 cells was inactivated by treatment with neuraminidase. Furthermore, LTIIa binding was blocked by tetanus toxin C fragment, which binds to gangliosides GD1b and GT1b. These findings support the hypothesis that ganglioside GD1b, or possibly a glycoconjugate with a GD1b-like oligosaccharide, is the functional receptor for LTIIa on T84 cells. The LTIIa-receptor complexes from T84 cells were associated with detergent-insoluble membrane microdomains (lipid rafts), extending the correlation between toxin binding to lipid rafts and toxin function that was previously established for CT. However, the extent of association with lipid rafts and the magnitude of the Cl(-) secretory response in T84 cells were less for LTIIa than for CT. These properties of LTIIa and the previous finding that enterotoxin LTIIb binds to T84 cells but does not associate with lipid rafts or elicit a Cl(-) secretory response may explain the low pathogenicity for humans of type II enterotoxin-producing isolates of E. coli.

Bacterial Toxins↗

PubMed2004

egc-Encoded superantigens from Staphylococcus aureus are neutralized by human sera much less efficiently than are classical staphylococcal enterotoxins or toxic shock syndrome toxin.

PCR was employed to determine the presence of all known superantigen genes (sea, seq, and tst) and of the exotoxin-like gene cluster (set) in 40 Staphylococcus aureus isolates from blood cultures and throat swabs; 28 isolates harbored superantigen genes, five on average, and this strictly correlated with their ability to stimulate T-cell proliferation. In contrast, the set gene cluster was detected in every S. aureus strain, suggesting a nonredundant function for these genes which is different from T-cell activation. No more than 10% of normal human serum samples inhibited the T-cell stimulation elicited by egc-encoded enterotoxins (staphylococcal enterotoxins G, I, M, N, and O), whereas between 32 and 86% neutralized the classical superantigens. Similarly, intravenous human immunoglobulin G preparations inhibited egc-encoded superantigens with 10- to 100-fold-reduced potency compared with the classical enterotoxins. Thus, there are surprisingly large gaps in the capacity of human serum samples to neutralize S. aureus superantigens.

Adult↗

PubMed2005

Differential binding of Escherichia coli enterotoxins LT-IIa and LT-IIb and of cholera toxin elicits differences in apoptosis, proliferation, and activation of lymphoid cells.

Cholera toxin (CT), LT-IIa, and LT-IIb are potent adjuvants which induce distinct T-helper (Th)-cell cytokine profiles and immunoglobulin G (IgG) subclass and IgA antibody responses. To determine if the distinct immune regulatory effects observed for LT-IIa, LT-IIb, and CT are elicited by binding of the enterotoxins to their cognate ganglioside receptors, the lineages of lymphoid cells that interact with the three enterotoxins and their effects on various lymphocyte responses in vitro were evaluated. Binding patterns of LT-IIa, LT-IIb, and CT to several lymphoid cell populations were distinctive for each enterotoxin. LT-IIa and CT, but not LT-IIb, induced apoptosis in CD8(+) T cells. LT-IIa(T34I), a mutant with no detectable binding to gangliosides, did not induce apoptosis. Blockade of GM(1) on the surface of CD8(+) T cells by LT-IIa(T14I), a mutant that binds only to GM(1) but does not induce apoptosis, did not inhibit induction of apoptosis by LT-IIa. Mitogen-induced proliferation of CD8(+) T cells was abrogated by treatment with CT, while resting CD8(+) T cells which were sensitive to LT-IIa-induced apoptosis became more resistant to apoptosis after mitogen activation. Exposure to CT, but not to LT-IIa or LT-IIb, inhibited mitogen-driven CD4(+) T-cell proliferation and expression of CD25 and CD69. In mitogen-stimulated B cells, CT, but not LT-IIa or LT-IIb, enhanced expression levels of CD86, while only CT induced B-cell differentiation into plasma cells. Thus, LT-IIa, LT-IIb, and CT exhibit distinguishable immunomodulatory properties which are likely dependent upon their capacities to recognize different ganglioside receptors on lymphocytes.

Animals↗

PubMed1974

Staphylococcal enterotoxin synthesis during the exponential, transitional, and stationary growth phases.

Small inocula (1 to 10 colony-forming units per ml of broth) of Staphylococcus aureus strains S-6, S-6R, and FRI-100 were employed to study growth and enterotoxin synthesis in 4% protein hydrolysate powder broths. For each strain, the exponential growth phase ended once the population approached 10(9) to 2 x 10(9) colony-forming units per ml. By that time, the concentrations of enterotoxins A and B reached the minimal level (1 to 2 mug/ml) at which the single gel diffusion tube method becomes applicable. By microslides and reverse passive hemagglutination, enterotoxins A and B were found to be synthesized during the exponential growth phase, but at different exponential rates.

Culture Media↗

PubMed1974

Scanning density gradient isoelectric focusing of Staphylococcus aureus enterotoxins B and C.

Purified Staphylococcus aureus enterotoxins B and C(1), the causative agents of staphylococcal food poisoning, were resolved into several components by scanning isoelectric focusing in sucrose density gradients in the absence and presence of 6 M urea and 5 mM dithiothreitol. The observed heterogeneity persisted in the denaturing medium, which suggests that the primary structure of protein enterotoxins B and C(1) may be partly responsible for the isoelectric point differences of the various forms. To our knowledge, the scanning isoelectric focusing patterns of staphylococcal enterotoxins B and C(1) are reported for the first time.

Centrifugation, Density Gradient↗

PubMed1980

Molecular comparison of plasmids encoding heat-labile enterotoxin isolated from Escherichia coli strains of human origin.

The molecular properties of enterotoxin (Ent) plasmids from 12 Escherichia coli strains of human origin were examined. Ten strains belonged to the O78 serogroup, and the remainder were of serogroup O7 or O159. Eleven plasmids coded for heat-labile enterotoxin (LT), and one coded for heat-stable enterotoxin (ST) and LT. The results of restriction enzyme digests and deoxyribonucleic acid reassociation experiments showed that all of the Ent plasmids were related, and supported the subdivision of the LT plasmids into three groups based on their genetic properties (M. M. McConnell et al., J. Bacteriol. 143: 158-167, 1980). Within group 1, two plasmids from South African strains were indistinguishable but differed in EcoRI and HindIII digests from the LT plasmid that originated from an Ethiopian strain. The three plasmids had >70% homology. The two non-autotransferring group 2 plasmids identified in O78.H11 strains from Bangladesh were indistinguishable. The group 3 plasmids were from strains belonging to serogroups O7 and O78 isolated in Bangladesh, India, and Thailand. They shared >95% homology but showed slight differences in fragment patterns when treated with EcoRI and HindIII. There was 60 to 70% homology between the plasmids of groups 1 and 3, and the group 2 plasmid had 40 to 50% homology with members of these two groups. The autotransferring Ent plasmids had up to 40% homology with R factors of incompatibility groups FI, FII, and FIV.

Bacterial Toxins↗

PubMed1981

Escherichia coli heat-labile enterotoxin genes are flanked by repeated deoxyribonucleic acid sequences.

The enterotoxin regions of the heat-labile and heat-stable enterotoxin (LT+ ST+) plasmid, pJY11, originating in a clinically isolated Escherichia coli strain, have been isolated as various-sized deoxyribonucleic acid (DNA) fragments by using cloning vehicles. The structure of the LT+ region and its neighboring DNA regions was studied by utilizing these recombinant plasmids. The LT+ region consisted of at least two genes, toxA and toxB, which could complement each other in trans. The toxA- and toxB-encoded polypeptides (LT subunits A and B, respectively) were identified by their immunological cross-reactivity with Vibrio cholerae enterotoxin subunit A or B. These tox genes and the promoter(s) were localized with respect to the restriction endonuclease cleavage map. The LT+ region was flanked by repeated DNA sequences (designated as beta). Another tox gen(s), encoding ST (designated as toxS), which was also flanked by inverted, repeated DNA sequences (designated as alpha), was located between one of the beta sequences and the LT+ region. These novel DNA structures (beta-alpha-toxS-alpha-toxA-toxB-beta) suggest the possibility that the LT+ region is on a transposon containing an ST transposon within the structure.

Bacterial Toxins↗

PubMed1987

Transient entry of enterotoxin subunits into the periplasm occurs during their secretion from Vibrio cholerae.

Cholera toxin and heat-labile enterotoxin (LT) are structurally similar oligomeric proteins which are capable of being efficiently secreted from Vibrio cholerae. Here we report that these proteins transiently enter the periplasm of V. cholerae as they traverse the cell envelope to reach the extracellular milieu. Pulse-chase experiments on V. cholerae TRH7000 harboring an LT-encoding plasmid revealed that radiolabeled LT A and B subunits entered the periplasm rapidly, followed by their slow efflux (half-time, 13 min) into the medium. LT B-subunit efflux from the periplasm was calculated to be at a rate of ca. 170 monomers per min per cell (which is equivalent to 34 assembled LT holotoxin molecules per min per cell). These values were estimated to be sufficient to account for the increase in extracellular enterotoxin concentration during exponential cell growth. Thus, all enterotoxin subunits which are secreted into the medium can be assumed to be channelled via the periplasm. These findings led to an improved model of the pathway of toxin secretion by V. cholerae.

Chromosome Deletion↗

PubMed1988

Staphylococcal enterotoxin B gene is associated with a discrete genetic element.

The chromosomal location of the enterotoxin B gene in Staphylococcus aureus is unknown. Southern hybridization analysis of the chromosomal DNA from several enterotoxin B (SEB)-producing strains has shown that at least 26.8 kilobases (kb) of DNA is associated with the enterotoxin B gene (entB). We have found that one end of the entB element is located approximately 1.5 kb downstream of the entB gene. The chromosomal region adjacent to this end of the entB element was found to be homologous in several SEB-producing (SEB+) and SEB-nonproducing (SEB-) S. aureus strains. The chromosomes of all the SEB+ strains studied were homologous for at least 24 kb upstream of the entB gene. Some naturally occurring SEB- strains lacked the entire entB element, while others showed variable homology to the region upstream of the entB gene. These data suggest that the entB gene is part of a discrete genetic element that is at least 26.8 kb in size.

Cloning, Molecular↗

PubMed1989

Nucleotide sequence of the type C3 staphylococcal enterotoxin gene suggests that intergenic recombination causes antigenic variation.

The nucleotide sequence of the structural gene for staphylococcal enterotoxin type C3 (entC3) was determined. This gene contains 798-base-pair open reading frame that encodes a protein of 266 amino acid residues. Sequence analysis suggests that staphylococcal enterotoxin type C3 is synthesized in a precursor form that is processed to yield a mature extracellular form of 238 amino acid residues (molecular weight, 27,438). The entC3 gene is closely related to the gene for staphylococcal enterotoxin type C1, with 98% nucleotide sequence identity. Sequence comparisons between the entC3, entC1, and entB genes suggest that an ancestral entC1-like gene was formed by recombination between the entC3 and entB genes.

Amino Acid Sequence↗

PubMed1964

Relation of pyrogenic and emetic properties of enterobacteriaceal endotoxin and of staphylococcal enterotoxin.

Martin, William J. (College of Medicine, University of Utah, Salt Lake City), and Stanley Marcus. Relation of pyrogenic and emetic properties of enterobacteriaceal endotoxin and of staphylococcal enterotoxin. J. Bacteriol. 87:1019-1026. 1964.-The pyrogenic, endotoxic fraction of enterobacteriaceal organisms, isolated in a relatively impure or purified state, is both pyrogenic in rabbits and cats as well as emeticogenic in cats in microgram amounts. Employing classical methods for preparation of enterobacteriaceal endotoxin from known enterotoxic strains of Staphylococcus aureus yielded preparations with less than one-hundredth the activity of the enterobacteriaceal material. However, a purified enterotoxin material from an S. aureus strain, with protein-like rather than polysaccharidelike properties, was found to be both pyrogenic and emeticogenic in microgram amounts. These results suggest the probability that the enterobacteriaceal pyrogenemetic substance(s) is a significant part of the whole cell, whereas the staphylococcal enterotoxin is elaborated as a metabolic product which apparently does not accumulate in the whole cell.

Animals↗

PubMed1969

Regulation of staphylococcal enterotoxin B.

Several factors influenced the formation of enterotoxin B by Staphylococcus aureus strain S-6. In the standard casein hydrolysate medium, toxin was not produced in detectable quantities during exponential growth; it was produced during the post-exponential phase when total protein synthesis was arithmetic. The rate of toxin synthesis was much greater than the rate of total protein synthesis. The appearance of enterotoxin was inhibited by chloramphenicol; thus, the presence of toxin was dependent on de novo protein synthesis. When low concentrations of glucose (<0.30%) were added to the casein hydrolysate medium, growth was diauxic; glucose was completely metabolized during the first growth period. During the second growth period, enterotoxin was synthesized. In unbuffered casein hydrolysate medium containing excess glucose, toxin synthesis was completely repressed. The absence of toxin production under such conditions might be explained by the low (4.6) pH resulting from the acid end products of glucose metabolism. At pH <5.0, little or no toxin was produced. Toxin synthesis was initiated in the presence of glucose when the medium were buffered at any pH above 5.6. In such media, the differential rates of toxin synthesis, with respect to the rates of total protein synthesis, were lower than the differential rates in casein hydrolysate medium alone. Addition of glucose to a culture synthesizing toxin resulted in an immediate decrease in the differential rate without any change in pH. Thus, toxin synthesis appeared to be regulated by catabolite repression.

Bacterial Proteins↗

PubMed1979

Evaluation of a ganglioside immunosorbent assay for detection of Escherichia coli heat-labile enterotoxin.

The GM1 ganglioside enzyme-linked immunosorbent assay (GM1-ELISA), an immunological method for detection of Escherichia coli heat-labile enterotoxin (LT), was quantitatively and qualitatively compared with the conventional adrenal cell test for the identification of LT-producing strains. A micromodification model of the assay was developed. Enterotoxin preparations from 120 E. coli isolates from individuals with diarrhea, which had been previously shown to be enterotoxigenic by the adrenal cell test, and from 44 control strains of E. coli were compared in parallel by the two methods. Quantitatively the covariation of the enterotoxin titers was highly significant (RS = 0.98, P less than 0.001), the GM1-ELISA being somewhat more sensitive than the adrenal cell test. The methodological error was less than 5% in both tests. Qualitatively the overall agreement for positive and negative reactions for the two methods was 89%. The GM1-ELISA is practical for routine use in the diagnosis of enterotoxigenic E. coli, especially in laboratories without facilities for cell culture.

Adrenal Glands↗

PubMed1980

Microtiter ganglioside enzyme-linked immunosorbent assay for vibrio and Escherichia coli heat-labile enterotoxins and antitoxin.

We have developed a microtiter enzyme-linked immunosorbent assay method for detecting the heat-labile enterotoxins of Vibrio cholerae and Escherichia coli using GM1 ganglioside as the base coat. This method compares favorably with a similar assay using anticholera toxin as the base coat, and with the Y1 adrenal cell assay. The assay should be useful in detecting enterotoxin production in E. coli and vibrios (including non-agglutinating Vibrio), in quantitating the toxin, and in determining binding properties of enterotoxins to ganglioside. The assay can also be used to quantitate antibodies which block the attachment of the toxin to the ganglioside.

Antitoxins↗

PubMed1981

Detection of Yersinia enterocolitica heat-stable enterotoxin by suckling mouse bioassay.

A comparison of heat-stable enterotoxins from Escherichia coli and Yersinia enterocolitica by the suckling mouse bioassay showed that whereas E. coli heat-stable enterotoxin evoked a maximum ratio of gut weight to remaining body weight after a 4-h incubation period, the maximum ratio for Y. enterocolitica was achieved at 2 h, decreasing thereafter to values regarded as negative (less than 0.083). This action of Y. enterocolitica heat-stable enterotoxin may give false-negative results for the standard suckling mouse bioassay.

Animals↗

PubMed1982

Detection of enterotoxigenic Escherichia coli in water by filter hybridization with three enterotoxin gene probes.

The DNA hybridization assay for genes encoding for Escherichia coli enterotoxins was used to examine water specimens in Thailand. In a reconstruction experiment, the DNA hybridization assay was 10(4) times more sensitive than testing random E. coli in the Y-1 adrenal and suckling mouse assays in identifying enterotoxigenic E. coli (ETEC) in water. Drinking and bathing water collected from 2 of 10 different homes of individuals with ETEC-associated diarrhea and 6% (5 of 78) and 11% (11 of 78) of drinking and bathing water samples collected from homes of individuals with diarrhea without ETEC infections, as well as 6% (5 of 77) and 8% (6 of 77) of drinking and bathing water collected from homes in which no inhabitants had diarrhea, were homologous with the DNA probes. Ten E. coli from each of the 31 water specimens which contained bacteria which were homologous with the DNA probes were tested in the Y-1 adrenal and suckling mouse assay. In only 2 of these 31 specimens could ETEC be identified with the standard assays. The DNA hybridization assay is a much more sensitive means of detecting organisms carrying genes coding for enterotoxin production than testing 10 individual colonies in the Y-1 adrenal and suckling mouse assays. This novel application of recombinant DNA technology provides a sensitive method of detecting organisms carrying genes coding for enterotoxin, and this method will be useful in defining the epidemiology of ETEC.

DNA, Bacterial↗

PubMed1983

Detection by a staphylococcal coagglutination test of heat-labile enterotoxin-producing enterotoxigenic Escherichia coli.

For detection of heat-labile enterotoxin-producing enterotoxigenic Escherichia coli, the staphylococcal coagglutination test reported by Brill et al. (J. Clin. Microbiol. 9:49-55, 1979) was modified to give better results. Staphylococcal cells were sensitized with anti-heat-labile enterotoxin antiserum and suspended in phosphate-buffered saline containing 0.5% bovine serum albumin, 0.05% Tween 80, 0.01% gelatin, and 0.02% NaN3. The test strain was cultured in 0.25 ml of Biken broth no. 2 in a test tube (12 by 100 mm) stood at an inclination of about 10 degrees to the horizontal. After incubation for 5 h at 37 degrees C, the cells were collected by centrifugation at 2,500 rpm for 15 min and suspended in 50 microliters of polymyxin B solution (20,000 IU/ml). The suspension was then incubated for 1 h at 37 degrees C and centrifuged at 2,500 rpm for 15 min, and 10 microliters of the supernatant was used for the test on a slide. The results of the modified test correlated completely with those obtained by the Biken test. The modifications of the staphylococcal coagglutination test described here allow for detection of heat-labile enterotoxin-producing enterotoxigenic E. coli within 6 to 7 h after inoculation of a test strain.

Agglutination Tests↗