Purification and characterization of a staphylococcal epidermolytic toxin

Exfoliative toxins of Staphylococcus aureus

Staphylococcus aureus is an important pathogen of humans and livestock. It causes a diverse array of diseases, ranging from relatively harmless localized skin infections to life-threatening systemic conditions. Among multiple virulence factors, staphylococci secrete several exotoxins directly associated with particular disease symptoms. These include toxic shock syndrome toxin 1 (TSST-1), enterotoxins, and exfoliative toxins (ETs). The latter are particularly interesting as the sole agents responsible for staphylococcal scalded skin syndrome (SSSS), a disease predominantly affecting infants and characterized by the loss of superficial skin layers, dehydration, and secondary infections. The molecular basis of the clinical symptoms of SSSS is well understood. ETs are serine proteases with high substrate specificity, which selectively recognize and hydrolyze desmosomal proteins in the skin. The fascinating road leading to the discovery of ETs as the agents responsible for SSSS and the characterization of the molecular mechanism of their action, including recent advances in the field, are reviewed in this article.

A novel method for rapid production and purification of exfoliative toxin A of Staphylococcus aureus

The exfoliative toxins of Staphylococcus aureus are the causative agents of the scalded-skin syndrome. Previously described methods of toxin production and purification require large quantities of culture medium, take a long time and often produce low yields of toxin. A novel method of toxin production and purification using a dialysis sac to separate the culture medium from the staphylococci is described. This method produces up to 12 mg of crude toxin per ml of bacterial cell culture bathing the surface of the dialysis sac within 36 h and almost 10 mg of purified toxin per ml of cell culture within 3 days, in contrast to previous procedures that took over a week to produce 0.1-1.0 mg ml(-1) crude toxin and less than 0.01 mg ml(-1) purified toxin. This rapid method of toxin production should speed up future research into the pathogenesis of the staphylococcal scalded-skin syndrome.

The epidermolytic (exfoliative) toxins of Staphylococcus aureus

Two epidermolytic toxins, produced by different strains of Staphylococcus aureus, split human skin at a site in the upper epidermis. Clinical effects are most common in infants, but adults are susceptible. Epidermolysis may also be observed in the mouse, in vivo and in vitro, and in a few other mammals. Recent in vitro experiments have demonstrated an inhibition by chelators and point to metal-ion, possibly Ca2+, involvement. The epidermolysis effect is insensitive to a wide range of other metabolic inhibitors. The toxin amino acid sequences are similar to that of staphylococcal proteinase, and new experiments by chemical modification and site-directed mutagenesis have shown that toxicity depends on 'active serine' residues of a catalytic triad similar to that found in serine proteases. Furthermore the toxins possess esterolytic activity, also dependent on the 'active serine' sites. However, the toxins have low or undetectable activity towards a range of peptide or protein substrates. In histological and related studies, the toxins bound selectively to an intracellular skin protein, profilaggrin, but there was no evidence that the toxin can enter intact epidermal cells. Therefore, although the circumstantial evidence that the toxins act by proteolysis is convincing, a specific skin proteolytic substrate for the toxin has not been identified.

Detection of staphylococcal exfoliative toxin by slide latex agglutination

A simple and rapid method in which slide latex agglutination was used was developed to detect the exfoliative toxin (ET) elaborated by clinical isolates. ET types A and B (ET-A and ET-B) were purified by plate gel isoelectrofocusing, and anti-ET sera were obtained by immunizing rabbits. A specific immunoglobulin G antitoxin was then prepared from the immunized rabbit sera by fast protein liquid chromatography, and latex particles were coated with the antitoxin. Of 74 staphylococcal strains isolated from patients with staphylococcal scalded skin syndrome, 61 strains were found to produce ET by the newborn mouse bioassay. All 61 strains were shown to be positive for ET-A and ET-B production by the slide latex agglutination method. The lowest concentration of ETs detected by the latex agglutination method was 0.5 microgram/ml, which was much lower than that detected by the double immunodiffusion method, with a sensitivity of 50 micrograms/ml. It is crucial to prove ET production by clinical isolates for the diagnosis and surveillance of staphylococcal scalded skin syndrome. The latex agglutination method is a sensitive, simple, and rapid test which can be used as an alternative to the newborn mouse bioassay.

Drug-induced toxic epidermal necrolysis (Lyell's syndrome) in a 4-year-old girl

Toxic epidermal necrolysis (Lyell's syndrome) with erythematous skin lesions and bulla formation developed in a 4-year-old girl. An accurate diagnosis using the cryostat technique on the top of a bulla was available within 1 h of hospital admission. The course was unusually mild, probably because of early treatment with corticosteroids. Skin prick tests revealed salicylamide as the agent responsible for inducing the disease. The patient was advised to avoid this substance for the rest of her life.

Preliminary crystallographic data for exfoliative toxin B from Staphylococcus aureus

The serotype B of exfoliative toxin, isolated from Staphylococcus aureus, strain TC 142, has been crystallized. The monoclinic crystals belong to space group P21, with a = 55.9 A, b = 107.9 A, c = 42.8 A, and beta = 90.9 degrees. The asymmetric unit contains two molecules of molecular weight 30,000.

Keratolinin: the soluble substrate of epidermal transglutaminase from human and bovine tissue

Substrates of human and bovine epidermal transglutaminase (glutaminyl-peptide gamma-glutamyltransferase, R-glutaminyl-peptide:amine-gamma-glutamyltransferase, EC 2.3.2.13) were isolated and purified by ion exchange chromatography and preparative zone electrophoresis. These substrates of Mr 36,000, which we propose to call keratolinin, incorporated dansylcadaverine and were precipitated by antibody. Keratolinin is ultimately polymerized on the inner leaflet of the keratinocyte membrane to form the cornified envelope. Each Mr 36,000 substrate was dissociated by chaotropic agents or detergents into noncovalent subunits; the Mr of these subunits was 6,000-6,200 on electrophoresis in 15% acrylamide/1% NaDodSO4/6 M urea gels. Isoelectric focusing of human or bovine keratolinin revealed two moieties separated by 0.3-0.4 pH unit (human, 5.4/5.0; bovine, 6.3/6.0). The two proteins were readily resolved by chromatofocusing and each isoelectric moiety of bovine keratolinin incorporated dansylcadaverine by epidermal transglutaminase and calcium and reacted with identity to antiserum to soluble Mr 36,000 keratolinin. Antiserum to human keratolinin failed to crossreact with its bovine counterpart. Antiserum to involucrin did not crossreact with either keratolinin or epidermis by immunodiffusion. Human and bovine epidermal keratolinins are biochemically similar but immunochemically distinct proteins from the epidermis. Involucrin appears only in significant quantities in cell culture.

A comparative study of two serotypes of epidermolytic toxin from Staphylococcus aureus

Two serotypes of epidermolytic toxin were purified from culture filtrates of different strains of Staphylococcus aureus. The amino acid composition of the proteins is similar, each containing no cystine and one methionine, but type ii contains no tryptophan, whereas type i has 1 mol/mol protein. The molecular weights of type i and type ii toxins were 30,000 and 29,500, respectively, as found by SDS-polyacryamide gel electrophoresis and confirmed by studies of CNBr fragments and tryptic peptides. Dansylation gave a single different N-terminal amino acid for each toxin; the C-terminus of each is lysine. Peptide mapping of tryptic digests showed that very few peptides are common to the two amino acid sequences.

Nonenteric toxins of Staphylococcus aureus

Images

Purification and characterization of different types of exfoliative toxin from Staphylococcus aureus

Exfoliative toxin was isolated from strain DI of Staphylococcus aureus using carboxymethyl cellulose and hydroxylapatite chromatography. This purified toxin was compared with that produced by strain TA. The specific biological activity of the two toxins was the same, but they were serologically distinct. These strains have different loci (plasmid or chromosomal) for toxin production; differences were seen in molecular weight and amino acid composition. N-terminal amino acid sequences from the two strains showed significant homology using a single unit alignment shift.

The epidermolytic toxin of Staphylococcus aureus: its failure to bind to cells and its detection in blister fluids of patients with bullous impetigo

Radioiodinated staphylococcal epidermolytic toxin was found not to bind to erythrocytes, blood leukocytes, trypsin-dispersed keratinocytes, epidermis or whole skin. Moreover the toxin could not be found to bind to murine epithelia by indirect immunofluorescence methods. However, the toxin, measured by radioimmunoassay, could be eluted from the skin of mice undergoing epidermolysis following intraperitoneal injection of toxinogenic Staphylococcus aureus. Furthermore, epidemolysin was measured in the blister fluid of 3 of 5 children with bullous impetigo but not in blister fluid from control patients with other blistering eruptions. Thus epidermolysin has been demonstrated to be present in lesions of the staphylococcal epidermolytic toxin syndrome but its mechanism of action does not involve binding to cells.

Molecular and serological differentiation of staphylococcal exfoliative toxin synthesized under chromosomal and plasmid control

Evidence for the existence of two molecular species of exfoliative toxin (ET) synthesized by phage group II Staphylococcus aureus under chromosomal and plasmid control is presented. Serological evidence that these molecular species of toxin are distinct from each other is given. The plasmid-controlled toxin was synthesized along with the chromosomally controlled toxin by the group II UT0002 strain, whereas another group II strain, UT0007, synthesized only the plasmid-controlled toxin. The molecular weight of the plasmid-controlled toxin was slightly less than that of the chromosomally controlled type and could be separated from the latter on 12.5% sodium dodecyl sulfate (SDS)-polyacrylamide slab gels. On 7.5% SDS-polyacrylamide cylindrical gels there was no hint of heterogeneity, and both ETs migrated together as a single homogeneous band. The existence of two serotypes of ET among phage group II strains complicates interpretation of previous work in this field and makes necessary the preparation of two different antigens for radioimmunobinding assays. Discovery of these ET serotypes provided an explanation for previously reported low binding by rabbit hyperimmune serum (B. Wiley, L. Glasgow, and M. Rogolsky, Infect. Immun. 13:513-520, 1976) in the radioimmunobinding test. A molecular species of ET differing from each of the other two serotypes was isolated from cultures of a phage group III S. aureus. This ET produced scalding in suckling mice and was lower in molecular weight than the ET produced under plasmid control by group II strains. Preliminary serological studies indicated that the ET in the group III strain is closely related to or possibly identical to the group II toxin produced under plasmid control.

The staphylococcal scalded skin syndrome. An experimental histochemical and electron microscopic study

Histochemical and electron microscopic studies were carried out on the newborn mouse model of the staphylococcal scalded skin syndrome to investigate the mechanism of action of the staphylococcal epidermolytic toxin that causes it. Histochemical studies showed that an intra-epidermal split develops below the subcorneal zone which is rich in catabolic enzymes (the so-called esterase-acid phosphatase-rich band). However, histochemical alterations in the enzyme pattern could not be demonstrated. The earliest change revealed by electron microscopy was a widening of the intercellular space, with the formation of microvilli at the level between the stratum spinosum and stratum granulosum where the split later occurs. A clearing of the peripheral cytoplasm along the cell membranes was also revealed. In pre-split areas, adhesion between cell membranes of adjacent cells seems to be lost; desmosomes continue to hold the cells together but the split develops when these are broken by mechanical pressure. Later, damaged cell membranes may be seen. Extracellular keratinosomes remain unchanged. Although these findings do not agree with the already divergent results of other studies, they help support the findings of all groups that cases of the Lyell syndrome produced by staphylococci do not occur through necrolysis; it is therefore inappropriate to continue applying the term 'toxic epidermal necrolysis' to such cases.

Production and properties of a staphylococcin genetically controlled by the staphylococcal plasmid for exfoliative toxin synthesis

Previous data from this laboratory showed that certain phage group 2 staphylococci contain a large 56S virulence plasmid containing genes that code for both exfoliative toxin (ET) and a specific staphylococcin. Optimal cultural conditions for bacteriocin production were similar to those found for ET production. The bacteriocin is an extracellular product produced in small quantities that can be neither extracted from cell pellets with 1 M NaCl nor induced with mitomycin C. The staphylococcin is active against a wide variety of gram-positive organisms and also against group 2 staphylococcal strains that have been cured of the plasmid carrying the staphylococcin marker. The bacteriocin is not inactivated by oxidation, mechanical agitation, or boiling for 15 min. It is sensitive to the action of trypsin and Pronase but not lysostaphin and is stable within a pH range of 4 to 9. It has an isoelectric point of approximately 7.7. Removal of the ampholytes and glycerol from electrofocused staphylococcin preparations resulted in total loss of bacteriocin activity.

Measurement of the staphylococcal epidermolytic toxin: a comparison of bioassay, radial immunodiffusion, and radioimmunoassay

Three methods of measuring the epidermolytic toxin Staphylococcus aureus-bioassay in newborn mice, radial immunodiffusion, and radioimmunoassay-were compared for reproducibility, specificity, and sensitivity. The bioassay is highly specific and remains the only functional assay. It is reproducible only if newborn mice of the same age are used. The time required for epidermolysis follows a dose-response relationship only if concentrations of toxin large enough to cause peeling in 90 min or less are used. This limits the sensitivity of the bioassay to about 5 mug per ml. Single radial immunodiffusion in agar is a specific and reproducible assay method, but its sensitivity is also about 5 mug per ml. A radioimmunoassay was established by the Farr technique using purified epidermolysin radiolabeled with 125iodine. This assay was highly reproducible and specific. The staphylococcal products, alpha-toxin and enterotoxins A and B, did not cross-react with anti-epidermolysin antibodies. The sensitivity of the radioimmunoassay is 20 ng per ml.