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PubMed1992

Induction of cytokines in human whole blood cultures by a mitogen derived from Mycoplasma arthritidis and by staphylococcal enterotoxin B.

Mycoplasma arthritidis produces a so-far only partially characterized soluble material (MAS) that has a potent mitogenic effect on T lymphocytes of several species. Similar to staphylococcal enterotoxins and a number of related toxins secreted by other species of bacteria, nanogram quantities of these so-called superantigens are sufficient to induce significant amounts of cytokines in the supernatant of lymphocyte cultures. Induction of interleukin-6 (IL-6) by MAS in murine bone marrow-derived macrophages has recently been described. In our study, we examined the differential effects of MAS and Staphylococcus aureus enterotoxin B (SEB) on human blood cells. When compared to MAS, SEB induced a higher proliferative response and, accordingly, a higher release of IFN-gamma. In contrast, large amounts of the macrophage products IL-1, IL-6 and tumor necrosis factor alpha (TNF-alpha) were observed in supernatants of cell cultures stimulated with MAS, whereas only small amounts were induced by SEB. Staphylococci and mycoplasmas are responsible for a number of diseases with various symptoms in man and animals. Our results suggest that SEB and MAS show different qualities in lymphocyte and macrophage stimulation which may be relevant in the pathogenesis of diseases.

Antigens↗

PubMed1998

Growth and enterotoxin production by diarrhoeagenic Bacillus cereus in dietary supplements prepared for hospitalized HIV patients.

This study was initiated because of an increase in diarrhoeal episodes in a ward caring for patients infected with the human immunodeficiency virus (HIV). An examination of hospital-prepared dietary supplements (build-up food) found Bacillus cereus to be a potential problem. Due in part to inadequate refrigeration conditions (13 +/- 4 degrees C), the microbial flora in commercially pasteurized semi-skimmed milk (PSSM) reached potentially hazardous levels (> 10(6) cfu/mL). While refrigerated PSSM did not support enterotoxin production, reconstitution of build-up powder in PSSM followed by storage in the HIV ward (4 h at 28 +/- 3 degrees C) resulted in growth of B. cereus (> 10(7) cfu/mL) and synthesis of diarrhoeal enterotoxin. While insufficient epidemiological data was available to establish conclusively a causal relationship between patients' symptoms and source, the study highlights a potential B. cereus problem with hospital-prepared dietary supplements and recommendations are proposed to prevent this re-occurrence.

Bacillus cereus↗

PubMed2000

Adjuvant action of Escherichia coli enterotoxin for delayed-type hypersensitivity to Oka vaccine virus on pernasal co-administration in mice.

The usefulness of a mutant of Escherichia coli enterotoxin for the induction of cellular immunity to varicella-zoster virus as a mucosal adjuvant is assessed in mice. When a commercially available live varicella vaccine (the Oka strain) and toxin were once administered simultaneously via the nasal route, delayed-type hypersensitivity to Oka vaccine virus was significantly induced and detected by footpad test in mice. Moreover, when spleen cells from mice immunized with the vaccine and toxin were re-stimulated with live vaccine in vitro, they showed more thymidine uptake and produced more IL-2 than those from mice immunized with the vaccine alone. These results suggest that mutant enterotoxin has adjuvant action to induce a specific delayed-type hypersensitivity to Oka vaccine virus on nasal co-administration with live vaccine virus.

Adjuvants, Immunologic↗

PubMed2001

PCR detection and prevalence of alpha-, beta-, beta 2-, epsilon-, iota- and enterotoxin genes in Clostridium perfringens isolated from lambs with clostridial dysentery.

Clostridium perfringens isolated from lambs with dysentery (n=117) were analysed by a DNA amplification technique, the polymerase chain reaction (PCR), in order to determine the prevalence of the alpha-, beta-, beta 2-, epsilon-, iota- and enterotoxin genes. The most prevalent toxin type of C. perfringens found was type B, containing the alpha-, beta-, and epsilon-toxin genes, representing 46% of the cases with clostridial dysentery. C. perfringens type C containing the alpha-, and beta-toxin genes was isolated in 20% and type D, which is characterized by the alpha- and epsilon-toxin genes, was isolated in 28% of all isolates. The recently discovered, not yet assigned beta 2-toxigenic type of C. perfringens was represented in 6% of all isolates. No C. perfringens type A containing the alpha-toxin alone and no type E, which harbours the ADP-ribosylating iota-toxin, were found in the diseased animals. None of the samples contained the enterotoxin gene. Only one type of C. perfringens was found in a given herd, revealing the epidemiological use of PCR toxin gene typing of C. perfringens. The animals originated from 79 different herds with sizes ranging from 30 to 250 animals, bred in the area of northern Greece.

Animals↗

PubMed2003

A strategy based on 5' nuclease multiplex PCR to detect enterotoxin genes sea to sej of Staphylococcus aureus.

We describe the development of a strategy based on 5' nuclease multiplex PCR for the rapid detection of nine enterotoxin genes (sea, seb, sec, sed, see, seg, seh, sei, sej) of Staphylococcus aureus. The genotyping scheme consists in identifying these nine enterotoxin genes by three 5' nuclease Triplex-PCR assays. The strategy was evaluated using a collection of S. aureus reference strains previously examined with conventional PCR assays, and by testing previously characterized food S. aureus field strains. The 5' nuclease Triplex-PCR assays correctly detected the se genes in all the reference strains. In tests with field strains there was generally excellent agreement with the results obtained by conventional PCR, except for some strains harbouring variant se genes. The detection limits of the Triplex-PCR assays evaluated using fivefold dilution of recombinant plasmids for each se gene ranged from 16 to 2000 copies of target se genes in the PCR tube. The 5' nuclease Triplex-PCR assays developed are fast and specific, and provide a useful diagnostic tool for the detection and genotyping of se genes. The development of this method is an improvement that should facilitate epidemiological investigations of staphylococcal food poisoning outbreaks.

Base Sequence↗

PubMed1996

Overlapping cases with psoriasis and Sjögren syndrome: a study of lymphocyte response to staphylococcal enterotoxin B.

Sjgren syndrome (SjS) is an auto-immune disease and immunological mechanisms have recently been suggested in the pathogenesis of psoriasis; however, co-existence of these diseases is relatively rare. To determine whether or not there exist the nature of common underlying abnormalities, five patients with psoriasis and SjS were studied. Two patients had psoriasis vulgaris (PV), two had psoriasis arthropathica (PA), and the other had generalized pustular psoriasis (GPP). Lymphocyte response against staphylococcal enterotoxin B was examined by 3H-thymidine incorporation. In one patient with GPP, T-cell receptor (TCR) V beta repertoire of infiltrating T-cells into the lesional skin was examined by reverse transcriptase-polymerase chain reaction (RT-PCR). Stimulation index (S.I.) level of patients with psoriasis and SjS did not show any significant increases compared with patients with psoriasis or SjS alone; however, one patient with PV and SjS, who showed several serological immune imbalances, demonstrated a significant increase of S.I. level. Analysis of TCR V beta repertoire of the lesion of GPP showed strong expression of V beta 14 and 16 with mild expression of V 13-2 and 19, which may suggest that TCR V beta repertoire became oligoclonal in case of complication of these two disorders. In conclusion, our data did not suggest any common immunological responses to staphylococcal enterotoxin in induction of both psoriasis and SjS.

Adult↗

PubMed1995

Crystal structure of the superantigen enterotoxin C2 from Staphylococcus aureus reveals a zinc-binding site.

BACKGROUND: Staphylococcus aureus enterotoxin C2 (SEC2) belongs to a family of proteins, termed 'superantigens', that form complexes with class II MHC molecules enabling them to activate a substantial number of T cells. Although superantigens seem to act by a common mechanism, they vary in many of their specific interactions and biological properties. Comparison of the structure of SEC2 with those of two other superantigens--staphylococcal enterotoxin B (SEB) and toxic shock syndrome toxin-1 (TSST-1)--may provide insight into their mode of action. RESULTS: The crystal structure of SEC2 has been determined at 2.0 A resolution. The overall topology of the molecule resembles that of SEB and TSST-1, and the regions corresponding to the MHC class II and T-cell receptor binding sites on SEB are quite similar in SEC2. A unique feature of SEC2 is the presence of a zinc ion located in a solvent-exposed region at the interface between the two domains of the molecule. The zinc ion is coordinated to Asp83, His118, His122 and Asp9* (from the neighbouring molecule in the crystal lattice). Atomic absorption spectrometry demonstrates that zinc is also bound to SEC2 in solution. CONCLUSIONS: SEC2 appears to be capable of binding to MHC class II molecules in much the same manner as SEB. However, structure-function studies have suggested an alternative binding mode that involves a different site on the toxin. The zinc ion of SEC2 lies within this region and thus may be important for complex formation, for example by acting as a bridge between the two molecules. Other possible roles for the metal cation, including a catalytic one, are also considered.

Amino Acid Sequence↗

PubMed2003

Prediction of the multimeric assembly of staphylococcal enterotoxin A with cell-surface protein receptors.

Staphylococcal enterotoxin A (SEA) cross-links two class II major histocompatibility complex (MHC) molecules and forms a multimeric assembly with T-cell receptors (TcRs). The X-ray crystal structure of SEA has been solved, yet details describing molecular recognition and association remain unclear. We present a structural model for the interactions of SEA with cell-surface proteins. Molecular docking calculations predicting SEA association with the class II MHC molecule HLA-DR1 were performed by using a rigid-body docking method. Docked orientations were evaluated by a Poisson-Boltzmann model for the electrostatic free energy of binding and the hydrophobic effect calculated from molecular surface areas. We found that the best-scoring SEA conformers for the DR1alpha interface display a binding mode similar to that determined crystallographically for staphylococcal enterotoxin B bound to HLA-DR1. For the zinc-binding site of SEA, docking DR1beta yielded several orientations exhibiting tetrahedral-like coordination geometries. Combining the two interfaces, tetramers were modeled by docking an alphabeta TcR with trimolecular complexes DR1beta-SEA-DR1alpha and SEA-betaDR1alpha-SEA. Our results indicate that the complex DR1beta-SEA-DR1alpha provides a more favorable assembly for the engagement of TcRs, forming SEA molecular contacts that are in accord with reported mutagenesis studies. In contrast, the cooperative association of two SEA molecules on a single DR1 molecule sterically inhibits interactions with TcRs. We suggest that signal transduction stimulated by SEA through large-scale assembly is limited to four or five TcR-(DR1beta-SEA-DR1alpha) tetramers and requires the dimerization of class II MHC molecules, while TcR dimerization is unlikely.

Enterotoxins↗

PubMed1979

The occurrence of plasmids carrying genes for both enterotoxin production and drug resistance in Escherichia coli of human origin.

Twenty-three of 89 enterotoxigenic strains of Escherichia coli were resistant to one or more antimicrobial agents. Eleven strains transferred resistance directly and five transferred resistance after mobilization. In three cases a resistant recipient was enterotoxigenic. One of these strains contained a conjugative plasmid carrying genes for both drug resistance and enterotoxin production. In the two other strains genes for drug resistance and enterotoxin production were carried on separate co-transferable plasmids.

Bacteriocin Plasmids↗

PubMed1994

Clonal study of enterotoxin-B producing strains of Staphylococcus aureus.

Sixty-nine Staphylococcus aureus strains, 39 of which produced staphylococcal enterotoxin B (SEB+) and 14 of which were associated with toxic shock (TS+), were studied using the following markers: serotyping, phage typing, antibiotyping, ribotyping, zymotyping and pulsed-field electrophoresis typing. Analysis of the results showed that the enterotoxin B producing strains were derived from at least three clones: the first two consisted of methicillin-susceptible strains, while the third included the methicillin-resistant (MRSA) strains. TS+ strains of nongenital origin appeared to be distributed between the three clones, with no specific characters.

Bacteriophage Typing↗

PubMed2002

An outbreak of gastroenteritis in Osaka, Japan due to Escherichia coli serogroup O166:H15 that had a coding gene for enteroaggregative E. coli heat-stable enterotoxin 1 (EAST1).

In an outbreak of gastroenteritis on 23 July 1996, in Osaka, Japan, 54 of 91 persons who had attended a meeting the previous day became ill. Escherichia coli O166:H15 was isolated from stool specimens of patients (29/33, 88%). Laboratory tests for other bacterial pathogens and viruses were negative. The E. coli 0166 organisms did not adhere to HEp-2 cells in a localized, diffuse, or enteroaggregative manner. The organisms did not express known enterotoxigenic E. coli (ETEC) colonization factors. In polymerase chain reaction tests, the bacteria did not have coding genes for shigatoxin of enterohemorrhagic E. coli (EHEC), heat-labile, or heat-stable enterotoxin of ETEC, attachment and effacement (eaeA) of EPEC, or invasion (invE) of enteroinvasive E. coli (EIEC). Consequently, they could not be assigned to any of the recognized diarrhoeagenic groups of E. coli: EPEC, ETEC, EHEC, EIEC, enteroaggregative E. coli (EAggEC), or diffusely adhering E. coli. However, the organisms possessed the EAggEC heat-stable enterotoxin (EAST1) gene. To our knowledge, this is the first report of an outbreak caused by E. coli that did not have well-characterized virulence genes other than EAST1. The isolates showed the same DNA banding pattern in pulsed-field gel electrophoresis after digestion with the restriction enzymes XbaI or NotI. Three O166:H15 strains isolated from two sporadic cases and another outbreak during 1997-8 were distinct, indicating that multiple clones have spread already. We propose that diarrhoeal specimens should be examined for E. coli possessing the EAST1 gene.

Base Sequence↗

PubMed2000

Amperometric detection of Escherichia coli heat-labile enterotoxin by redox diacetylenic vesicles on a sol-gel thin-film electrode.

Supramolecular assemblies (bilayer vesicles) prepared from ferrocenic diacetylene lipid and the cell surface receptor ganglioside GM1 are utilized to construct an amperometric biosensor for Escherichia coli heat-labile enterotoxin on a sol-gel thin-film electrode. The bilayer vesicles adsorbed on the sol-gel film provide an open platform for molecular recognition, while the electrochemical communication between the incorporated redox lipids and the electrode is influenced by the binding of the toxin. Cyclic voltammetric studies suggest a facile redox reaction for the adsorbed supramolecular assembly, which allows the sensor to detect enterotoxin up to 3 ppm (3.6 x 10(-8) M) concentration. The apparent diffusion coefficients for the redox lipids in the assembly were observed to be in the range of 4.73 x 10(-8) -2.30 x 10(-8) cm/s2. A mechanism of lateral electron transport of redox lipids controlled by biomolecular recognition is proposed.

Acetylene↗

PubMed1994

Structural characteristics for biological activity of heat-stable enterotoxin produced by enterotoxigenic Escherichia coli: X-ray crystallography of weakly toxic and nontoxic analogs.

Heat-stable enterotoxin (ST) produced by a pathogenic strain of Escherichia coli exerts its function by binding to a membrane-bound guanylyl cyclase on intestinal epithelial cell membranes, which in turn catalyzes the production of cyclic GMP as a second messenger in the cells. To elucidate the structural requirements for the biological activities of ST, we synthesized [Mpr5,Gly13]STp(5-17) and [Mpr5,Leu13]STp(5-17), which are weakly toxic and nontoxic analogs of STp, in which the toxic domain consists of the sequence from Cys at position 5 to Cys at position 17. In these analogs, Cys at position 5 is replaced by Mpr (beta-mercaptopropionic acid) and Ala at position 13 by Gly and Leu, respectively. We examined these analogs by X-ray diffraction analysis using direct methods and refined the structures to crystallographic R factors of 7.3% and 6.6% using 5492 and 5122 data, respectively, observed > 3 sigma (Fo) with a resolution of 0.89 A. These peptides have a right-handed spiral structure consisting of three structural segments: an N-terminal 3(10) helix, a central type I beta-turn, and a C-terminal type II beta-turn. These structures show minor differences from that of [Mpr5]STp(5-17), the fully toxic analog of heat-stable enterotoxin [Ozaki et al. (1991) J. Biol. Chem. 266, 5934-5941], suggesting that the decrease and loss of the biological activities of [Mpr5,Gly13]STp(5-17) and [Mpr5,Leu13]STp(5-17), respectively, are not caused by structural changes but are associated with the direct interaction of Ala13 with the receptor protein. Careful comparison of these structures in crystalline states revealed that ST has the following structural characteristics: (i) inherent flexibility at the junctions of the three segments and in the central segment, which includes the putative receptor-binding residues, Ala13, (ii) a specific hydrophobic character around the central segment, and (iii) an unexpected C-terminal folding similar to those of functionally unrelated peptides that are known to be ionophores.

Amino Acid Sequence↗

PubMed1991

Structural characterization of functionally important regions of the Escherichia coli heat-stable enterotoxin STIb.

The biological properties of the Escherichia coli enterotoxin STIb (STA-3, STh) reside in a 13 amino acid C-terminal domain, abbreviated STIb(6-18). This tridecapeptide contains six cysteine residues involved in three intramolecular disulfide bridges. The solution structure of STIb(6-18) has been modeled as a series of three consecutive reverse turns [Gariépy et al. (1987) Proc. Natl. Acad. Sci. U.S.A. 83, 8907-8911]. Synthetic tridecapeptide analogues of STIb(6-18) with single amino acid substitutions at non-cysteine sites, as well as a truncated decapeptide lacking one of the three disulfide bridges, were prepared in order to examine the relationship between primary sequence and biological activity. The relative affinity of each analogue for intestinal cell receptors only partially correlates with their dose-dependent ability to cause diarrhea in suckling mice, suggesting that subsaturation doses of the enterotoxin with respect to receptor occupancy on intestinal cells may be sufficient to cause diarrhea. Two substitutions in the central-turn region of the molecule, namely, Asn12----Ala and Ala14----D-Ala, resulted in a large decrease or loss of receptor binding activity as compared to native STIb(6-18), pointing out the functional importance of this region. Analogues containing replacements at other sites showed moderate to slight reductions in biological activity. In particular, residues in the C-terminal region appear to be less important for activity, although their presence remains essential, since a truncated analogue missing the last three amino acids is inactive.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1979

Purification and some physicochemical properties of staphylococcal enterotoxin D.

A method was developed for the isolation of staphylococcal enterotoxin D in highly purified form from cultures of Staphylococcus aureus strain 1151m. The method involves removal of the toxin from the culture supernatant fluid with the ion-exchange resin CG-50 followed by chromatography on carboxymethylcellulose (twice) and by gel filtration on Sephadex G-75 (twice). The purified toxin is homogeneous by polyacrylamide gel and sodium dodecyl sulfate-polyacrylamide gel electrophoresis and double gel diffusion tests. It is a simple, colorless, antigenic protein with an isoelectric point of 7.4 as determined by isoelectric focusing. Its molecular weight was determined to be 27 300 +/- 700 by molecular sieve chromatography on Sephadex G-100 and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Its serological activity is stable over a wide range of pH values (1.2--10.7). The enterotoxin consists of 236 amino acid residues and contains no free sulfhydryl groups. End-group analysis showed serine to be the NH2-terminal amino acid and lysine to be the COOH-terminal amino acid.

Amino Acids↗

PubMed1996

A pH-dependent conformational change in the B-subunit pentamer of Escherichia coli heat-labile enterotoxin: structural basis and possible functional role for a conserved feature of the AB5 toxin family.

The non-covalently associated B-subunit moieties of AB5 toxins, such as cholera toxin and related diarrheagenic enterotoxins, exhibit exceptional pH stability and remain pentameric at pH values as low as 2.0. Here, we investigate the structural basis of a pH-dependent conformational change which occurs within the B5 structure of Escherichia coli heat-labile enterotoxin (EtxB) at around pH 5.0. The use of far-UV CD and fluorescence spectroscopy showed that EtxB pentamers undergo a fully reversible pH-dependent conformational change with a pKa of 4.9 +/- 0.1 (R2 = 0.999) or 5.13 +/- 0.01 (R2 = 0.999), respectively. This renders the pentamer susceptible to SDS-mediated disassembly and decreases its thermal stability by 18 degrees C. A comparison of the pH-dependence of the structural change in EtxB5, with that of a mutant containing a Ser substitution at His 57, revealed that the pKa of the conformational change was shifted from ca. 5.1 to 4.4. This finding suggests that protonation of the imidazole side chain of His 57 might facilitate disruption of a spatially adjacent salt bridge, located between Glu 51 and Lys 91 in each B-subunit, thus triggering the conformational change in the pentameric structure. The pH-dependent conformational change was found to be inhibited when B-subunits bound to monosialoganglioside, GMI; and to have no effect on the stability of interaction between A- and B-subunits within the AB5 complex. This suggests that the conformational change is unlikely to have a direct involvement in toxicity. Conservation of the pH-dependent conformational change in the AB5 toxin family, combined with the potential exposure of the hydrophobic core of beta-barrel in the monomeric units, leads to the proposal that the conformational change may be the common feature that ensures the secretion of these proteins from the Vibrionaceae.

Amino Acid Sequence↗

PubMed2006

Development of a fluorescent latex microparticle immunoassay for the detection of staphylococcal enterotoxin B (SEB).

Staphylococcus aureus enterotoxin B (SEB) is a highly heat resistant enteric toxin with a potential as a biothreat agent. A sensitive method for the detection of staphylococcal enterotoxins is needed for food safety and food defense monitoring. The objectives of this research were to develop a competitive fluorescent immunoassay with detection of SEB below toxic levels of 1 ng/mL and to minimize sample preparation. Anti-SEB was immobilized onto carboxylated polystyrene microparticles, and SEB was labeled with fluorescein isothiocyanate (FITC). The concentrations of these reagents were optimized for the detection of SEB below 1 part per billion (1 ng/mL), and other assay conditions (sample volumes and incubation periods) were optimized. Drinking water and milk samples were spiked with 0.125-10 ng/mL SEB and were equilibrated overnight prior to analysis. The water and milk samples were directly analyzed, but heating the milk samples for 10 min at 90 degrees C improved the assay performance. SEB in samples bound with the anti-SEB linked to the latex followed by the competitive binding of SEB-FITC tracer. The excess, unbound tracer was separated by centrifugation, and the fluorescence density of the supernatant was measured. SEB was detected at levels as low as 0.125 ng/mL in drinking water and 0.5 ng/mL in whole milk. This fluorescent latex particle immunoassay will be utilized for the detection of SEB in various foods matrices.

Animals↗

PubMed1997

Digestion of staphylococcal enterotoxin by Bacillus natto.

Cooked rice contaminated with staphylococcal enterotoxin A (SEA) was mixed with 'natto', a Bacillus natto fermented soybean food, and the mixture was incubated at 37 degrees C for 1 h. Reversed passive latex agglutination (RPLA) tests performed on the mixture revealed that the RPLA titer against SEA was significantly reduced after incubation. Subsequent analytical tests showed that the SEA protein molecule was fragmented to small peptides by an extracellular protease, subtilisin, produced by B. natto. The proteolytic activity of B. natto was also found to be effective against other types of staphylococcal enterotoxins.

Agglutination Tests↗