Sensitive and specific detection of staphylococcal epidermolysins A and B in broth cultures by flow cytometry-assisted multiplex immunoassay

Two of the most common bacterial skin infections of young infants and children are bullous impetigo due to Staphylococcus aureus and its more acute form, staphylococcal scalded skin syndrome. Epidermolysin A (ETA), ETB and, possibly, ETD are responsible for these diseases, which may appear as epidemics in pediatric patients. We tested the reliability of a flow cytometry-assisted multiplex immunoassay (Bio-Plex system) for the detection of ETA and ETB. The Bio-Plex system was found to be highly specific and highly sensitive for toxin concentrations of between 2 and 80,000 pg/ml. The results of this assay were 100% identical to the results of a PCR-based method. We demonstrated that this test did not generate any cross-reactions with ETD-producing isolates. The level of detection of ETB by this test differed according to culture conditions and from isolate to isolate; these results must be taken into account for diagnostic purposes.

A multiplex PCR for detection of genes encoding exfoliative toxins from Staphylococcus hyicus

AIMS

To develop a multiplex PCR for detection of genes encoding the exfoliative toxins ExhA, ExhB, ExhC and ExhD from Staphylococcus hyicus and to estimate the prevalence of exfoliative toxins among Staph. hyicus isolates from Danish pig herds with exudative epidermitis (EE).

METHODS AND RESULTS

A multiplex PCR employing specific primers for each of the genes encoding four different exfoliative toxins was developed and evaluated using a collection of Staph. hyicus with known toxin type and a number of other staphylococcal species. A total of 314 Staph. hyicus isolates from pigs with EE were screened by multiplex PCR and the combined results of the present and previous investigations showed that ExhA, ExhB, ExhC and ExhD was found in 20, 33, 18 and 22%, respectively, of 60 cases of EE investigated.

CONCLUSIONS

This study has provided a new tool for detection of toxigenic Staph. hyicus and a more comprehensive picture of the prevalence of the Staph. hyicus exfoliative toxins in Danish pig herds.

SIGNIFICANCE AND IMPACT OF THE STUDY

The multiplex PCR can be used in studies on the prevalence of toxigenic Staph. hyicus elucidating the epidemiology of EE in pigs. The multiplex PCR is currently being used for selection of Staph. hyicus isolates for production of autogenous vaccine.

Recent developments in staphylococcal scalded skin syndrome

Staphylococcal scalded skin syndrome describes a spectrum of superficial blistering skin disorders caused by the exfoliative toxins of Staphylococcus aureus. In its severe form, the exfoliation can spread to cover the entire body surface area. Two S. aureus exfoliative toxin serotypes affecting humans have been identified, but their purpose and mechanism of action have remained elusive. Based on their interaction with human and mouse epidermis, their three-dimensional structure and site-directed mutagenesis studies, it is speculated that they act as atypical serine proteases, and desmoglein-1 has now been identified as the specific epidermal substrate. Recent studies also suggest that the toxins may have a unique superantigenic activity. Clinically, new rapid diagnostic tests have been developed, including one that is able to detect the toxins directly from serum. With early diagnosis and appropriate management, mortality in children remains low and long-term complications are rare because the lesions are superficial and heal rapidly without scarring. In adults, however, the condition carries a mortality of almost 60% despite aggressive treatment, usually because of serious underlying illness. The recent developments in our understanding of the exfoliative toxins should lead to new and improved diagnostic and therapeutic strategies, including the use of specific antixoxins to prevent exfoliation.

Development and evaluation of detection systems for staphylococcal exfoliative toxin A responsible for scalded-skin syndrome

Staphylococcal scalded-skin syndrome is usually diagnosed clinically by its characteristic exfoliating rash. Isolation of Staphylococcus aureus from the patient further supports the diagnosis. Several detection systems have been developed to determine whether the isolated strain produces exfoliative toxin, but none are routinely available in hospital laboratories. In a novel approach, we used computer models to predict the structure of the exfoliative toxins based on other serine proteases and to identify surface epitopes for the production of antibodies that specifically bound the exfoliative toxin A (ETA) serotype. Several rapid immunologically based diagnostic tests for ETA were developed with these antibodies and compared with existing systems. Our results showed that Western blot analysis using these antibodies was in complete correlation with PCR, which has been validated against the "gold standard" mouse model. On the other hand, the double-antibody enzyme-linked immunosorbent assay (ELISA) and Ouchterlony immunodiffusion assay gave unacceptably high false-positive results due to interference by staphylococcal protein A. This problem was successfully overcome by the development of a F(ab')(2) fragment ELISA, which was rapid and reproducible and was as sensitive and specific as PCR and Western blot analysis. The F(ab')(2) fragment ELISA is superior to existing diagnostic systems because it is quantitative, which may be related to the severity of the condition, and can detect amounts of exfoliative toxin in the picogram range directly from serum. This is the first detection system with the potential to confirm the diagnosis of staphylococcal scalded-skin syndrome from a routine blood test within 3 h of presentation.

Superantigen production by Staphylococcus aureus in psoriasis

BACKGROUND

Activation of T cells is believed to play a critical role in the pathogenesis of psoriasis. Recently, it has been proposed that psoriasis is a T-cell-mediated autoimmune reaction triggered by bacterial superantigen.

OBJECTIVE

We investigated whether patients with chronic plaque psoriasis bear superantigen-producing Staphylococcus aureus on the skin or the throat.

METHODS

S. aureus producing exfoliative toxin, staphylococcal enterotoxin B or toxic shock syndrome toxin 1 was isolated from the skin and throat of 100 psoriasis patients using Western blot analysis and polymerase chain reaction.

RESULTS

Only 5, 4 and 9 patients had super-antigen producing S. aureus identified on lesional skin, nonlesional skin and throat, respectively. The vast majority of patients did not bear superantigen-producing S. aureus.

CONCLUSION

We believe that superantigens are not essential in sustaining disease activity but may, instead, be exacerbating or triggering factors for some psoriasis patients.

[Neonatal staphylococcal epidermolysis due to maternal-fetal transmission]

INTRODUCTION

The staphylococcal scalded skin syndrome (SSSS) is due to exfoliative toxins A or B excreted by some strains of Staphylococcus aureus. This syndrome is exceptional in the first hours of life. We report a case of SSSS due to materno-fetal infection.

CASE REPORT

At 31 weeks of pregnancy a 40-year-old mother was febrile (39 degrees C) and a premature rupture of the amniotic sac occurred the following day. SSSS was diagnosed at 6 hours of life in the newborn, a 1760 g female. Staphylococcus aureus grew on the blood and vaginal bacterial cultures of the mother, as well as, from cultures of skin, nose, throat, and umbilical catheter in the newborn. The strains of Staphylococcus aureus isolated in the mother and the child had identical characteristic antibiotype and genotype by Random-PCR. The genes for both exfoliations A and B were present. Epidermization was rapidly obtained and no septicemia or septic complication was noted.

DISCUSSION

Staphylococcus aureus is usually responsible for nosocomial infections which occur in the early newborn period. In most cases, the infection is transmitted by a carrier who manipulates the child (family, visitors, nurse or medical staff). In our case, onset of SSSS early after birth suggested a perinatal transmission, due to lower genital tract infection in the mother. The presence of SSSS in the child and not in the mother may be explained by a massive perinatal infection and low elimination of the toxin in the newborn resulting in higher concentrations of exfoliative toxins in the blood.

Evaluation of the staphylococcal exotoxins and their specific IgE in childhood atopic dermatitis

BACKGROUND

Superantigenic exotoxins produced by Staphylococcus aureus and their specific IgE antibodies are thought to be important precipitating factors of atopic dermatitis (AD), but there are few reports evaluating these 2 factors at the same time.

OBJECTIVE

We examined whether the presence of the exotoxins sampled from the skin of patients with AD and the levels of anti-exotoxin IgE antibodies in their sera correlated with their severity of AD.

METHODS

Patients with mild-to-severe AD, 1 to 22 years of age, were evaluated by using Leicester's scoring system. Specific IgE antibodies against these exotoxins were determined by using ELISA. S aureus was isolated from 3 different areas of the skin. We examined whether the exotoxin (staphylococcal enterotoxin [SE]A, SEB, SEC, SED, and toxic shock syndrome toxin-1) could be detected.

RESULTS

The levels of SEB-specific IgE were correlated with the severity of AD. Five of 6 patients having very high SEB-specific IgE antibody titers were under 6 years of age, and SEB was most frequently isolated (41%). There was no difference in severity between patients with or without exotoxin-producing S aureus. The severity of 9 patients who had both exotoxin-producing S aureus on the skin and specific IgE antibody against the same exotoxin in sera was significantly higher than that of the other patients.

CONCLUSIONS

Anti-SEB IgE titers correlate well with the severity of AD. The presence of exotoxin-producing S aureus may precipitate AD through its specific IgE antibody.

Molecular epidemiology of staphylococcal scalded skin syndrome in premature infants

BACKGROUND

Outbreaks of nosocomial staphylococcal scalded skin syndrome (SSSS) in infants have been well-described associated with the well baby nursery or delivery room. We describe two cases of SSSS in very low birth weight infants in a neonatal intensive care unit (NICU) and the success of infection control strategies used to prevent an outbreak.

METHODS

Staphylococcal scalded skin syndrome was diagnosed in two infants in the NICU: Case I (a 47-day-old, formerly 530-g female); and Case II diagnosed 48 h later (a 41-day old, formerly 706-g female). Multiple infection control measures were implemented: (1) isolation and intravenous antibiotic treatment of cases; (2) placement of exposed infants into a cohort; (3) prophylactic mupirocin treatment of the anterior nares of all infants in the NICU and staff colonized with Staphylococcus aureus; and (4) personnel hand washing with hexachlorophene. Detection of exfoliative toxin A and studies to determine the genetic relatedness of S. aureus strains isolated from patients and staff were performed.

RESULTS

In addition to the two SSSS cases, S. aureus was isolated from 2 of 12 (17%) exposed asymptomatic infants, 2 of 20 (10%) ancillary staff, 8 of 30 (27%) nurses and 6 of 24 (25%) physicians. Exfoliative toxin A-producing strains were isolated from both cases and one asymptomatic infant. No toxin was expressed by strains isolated from staff. Pulse field gel electrophoresis demonstrated genetically identical strains of S. aureus from the two SSSS cases and the asymptomatic infant, whereas three staff members harbored strains genetically related to the case strain. Unexpectedly two additional unique clusters of genetically related S. aureus strains were identified from the surveillance cultures.

CONCLUSIONS

This report documents the rare occurrence of nosocomial SSSS attributed to transmission in the NICU among extremely low birth weight infants. Multiple infection control strategies were effective in limiting the outbreak. Molecular epidemiology investigation supported a unique S. aureus strain responsible for this event and the presence of bidirectional spread between staff and patients of non-toxin-producing strains.

Exfoliative toxin detection using reversed passive latex agglutination: clinical and epidemiologic applications

A rapid and simple method for detecting exfoliative toxin serotypes A and B from clinical isolates has been developed as a test kit (EXT-RPLA; Denka Seiken Co. Ltd., Niigata, Japan). This method is based on reversed passive latex agglutination. The detection limit of the EXT-RPLA observed for purified exfoliative toxin serotypes A and B was 1 ng/ml. We evaluated the clinical and epidemiologic uses of the EXT-RPLA. A total of 381 isolates of Staphylococcus aureus, 292 from various clinical specimens and 89 from the skin of dermatologic patients, were studied. The EXT-RPLA detected 19 exfoliative toxin producers, including 16 serotype A producers and 3 serotype B producers, but no double producers. The sensitivity and specificity of the EXT-RPLA were confirmed by the newborn mouse bioassay and a PCR assay for the structural genes for exfoliative toxin serotypes A and B (eta and etb, respectively). The overall positivity rate of exfoliative toxin producers was 5.0% (19 of 381), including 16 serotype A isolates and 3 serotype B isolates. Of the 89 isolates from the skin of dermatologic patients, 12 (13.5%) were positive for exfoliative toxin production. Only 2 (1.3%) of the 153 methicillin-resistant S. aureus isolates produced exfoliative toxin, while 17 (7.5%) of the 228 methicillin-sensitive isolates produced exfoliative toxin. The EXT-RPLA assay is a simple and reliable method for detecting exfoliative toxin, and we recommend its use for the rapid diagnosis of staphylococcal scalded skin syndrome. We also recommend its use for detection of this syndrome so that effective control measures can be taken against the spread of this syndrome.

Staphylococcal scalded skin syndrome in an immunocompromised adult

Staphylococcal scalded skin syndrome, a generalized exfoliative dermatitis complicating infections by exfoliative toxin-producing strains of Staphylococcus aureus, is rarely observed in adults. In contrast to mortality in infants, mortality in adults is usually high. A case of generalized staphylococcal scalded skin syndrome in an immunocompromised woman is reported. Culture of skin biopsy and pleural fluid yielded identical strains of staphylococcus aureus belonging to phage group II. Exfoliative toxins A and B were detected in both isolates. As far as can be determined, this is the first reported case of generalized staphylococcal scalded skin syndrome in an adult with detection of exfoliate toxins A and B in which the patient was treated successfully.

Staphylococcal scalded skin syndrome in an adult. Influence of immune and renal factors

We report a case of staphylococcal scalded skin syndrome in a 77-year-old man with an infected surgical wound. The patient was immunocompetent and had only mildly impaired renal function. The pathogenic and aetiological factors of the condition are discussed.

ELISA estimation of the binding of epidermolytic toxin to neonatal mouse skin

A sandwich ELISA, with antisera from rat and rabbit, was used to determine epidermolytic toxin (ET) to a limit of about 0.01 ng at 0.1 ng/ml. The binding of ET to the epidermis of skin discs was measured in vitro. The ability of the assay to discriminate between the two forms of the toxin was used to demonstrate that there was a saturable component of toxin binding to the epidermis. The rate of uptake, the effect of the inhibitor EGTA and comparative experiments with the inactive nitrated toxin confirmed that the observed binding is associated with toxigenesis. From measurements at toxin concentrations from 0.25 microgram/ml to 100 micrograms/ml, it was calculated that the saturable binding component has a Kd of about 2 micrograms/ml (approximately 60 nM) and a capacity of 0.5 ng per skin disc (1 ng per cm2 of epidermis).

Incidence and characterization of Staphylococcus aureus from the tongues of children

Three hundred and seven children who had no diseases other than dental disease were examined for their oral carriage of Staphylococcus aureus, the most common persistent human pathogen. Eighty-four percent of them were positive for staphylococci, and 33% were positive for S. aureus. Among the 100 strains of S. aureus isolated, 40 strains produced enterotoxin, and 19 strains produced exfoliative toxin. Their susceptibility to antibiotics was also investigated: Six strains demonstrated resistance to methicillin (MIC greater than or equal to 12.5 microgram/mL), and 50% of the isolates were borderline resistant (MIC of 3.13 to 6.25 micrograms/mL) to the drug. These data suggest that the mouths of children could be reservoirs of pathogenic S. aureus.

Purification of staphylococcal exfoliative toxin by high pressure liquid chromatography

Exfoliative toxin (ET) isolated from a clinical strain of Staphylococcus aureus was purified to homogeneity, using a 3-step HPLC system. NH2-terminal 20 amino residues of purified ET was found to be identical with ETA of S. aureus TA (7), S. aureus TC16 (9) and S. aureus ZM (10), but stability of purified ET was completely different from that of ETA. This purification system gave a high yield of pure ET, which exhibited higher purity than specimens purified by more complicated and time-consuming procedures. It is useful for small-scale purification for the comparative study of ET and easy to scale up for preparative purification.

Synthetic exfoliative toxin A and B DNA probes for detection of toxigenic Staphylococcus aureus strains

Two methods for the detection of exfoliative toxin (ET) from Staphylococcus aureus were compared: (i) a phenotypic assay, electrosyneresis, and (ii) a genotypic assay, staphylococcal DNA hybridization with oligodeoxynucleotide probes. The probes were chosen from the previously determined sequences of serotype A and B of ET, one probe for serotype A and another for serotype B. Strains exhibiting ET production in electrosyneresis always possessed the ET gene(s). Conversely, some strains not exhibiting ET production in electrosyneresis harbored the ET gene(s). The latter strains produced levels of ET. ET-negative phage group 2 strains of S. aureus as well as tested coagulase-negative staphylococci did not possess the ET gene(s). The sensitivity of the DNA hybridization technique was 10(6) bacteria or 100 ng of genomic DNA.

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.

Sequence determination and comparison of the exfoliative toxin A and toxin B genes from Staphylococcus aureus

The DNA encoding the exfoliative toxin A gene (eta) of Staphylococcus aureus was cloned into bacteriophage lambda gt11 and subsequently into plasmid pLI50 on a 1,391-base-pair DNA fragment of the chromosome. Exfoliative toxin A is expressed in the Escherichia coli genetic background, is similar in length to the toxin purified from culture medium, and is biologically active in an animal assay. The nucleotide sequence of the DNA fragment containing the gene was determined. The protein deduced from the nucleotide sequence is a polypeptide of 280 amino acids. The mature protein is 242 amino acids. The DNA sequence of the exfoliative toxin B gene was also determined. Corrections indicate that the amino acid sequence of exfoliative toxin B is in accord with chemical sequence data.

Importance of exfoliatin toxin A production by Staphylococcus aureus strains isolated from clustered epidemics of neonatal pustulosis

Clustered epidemics of pustulosis due to Staphylococcus aureus occurred in two geographically distant newborn nurseries. In nurseries A and B an attack rate of pustulosis of 0.8 and 2.0 cases per 100 live births occurred, respectively. Experimental phage type 1046/1116 belonging to phage group II dominated clustered epidemics in nursery A, while group II phage type 3A/3C/55/71 and 3A/3C/55 occurred in nursery B. Other group II strains also occasionally produced clustered epidemics. These epidemic strains were found to be making heat-stable dermal exfoliatin toxin A (ETA) which had a pI of 6.8 and a molecular weight of 32,000 and 33,000. ETA-bearing strains did not make bacteriocin. Children infected with ETA-producing strains developed extensive bullous pustulosis. Surveillance cultures of personnel revealed an ETA-bearing strain in only one person. This strain was not the same phage type as the epidemic cluster. In contrast, ETA-bearing epidemic strains were found in the inanimate environment of both nurseries. ETA protein acts as an important virulence factor in the production of neonatal pustulosis infection and appears to be linked with the ability of S. aureus organisms to stick to the inanimate environment.

Screening of clinical S. aureus-isolates for the production of exfoliative toxin. A methodological study

Screening S. aureus-isolates for the production of exfoliative toxin (ET) and discrimination between its two known variants (ETA, ETB) by immunodiffusion (ID), isoelectric focusing (IEF) and animal experiment were assessed methodologically using isolates from a patient with bullous impetigo and a patient with Ritter von Rittershain's disease. Only by animal assay one of the isolates could be identified as ET-producer. ID was used for the discrimination between ETA and ETB. It is concluded that the in-vivo assay for ET-production using live staphylococci can not yet be replaced by ID and IFE and that in patients with staphylococcal scalded skin syndrome swabs should be taken from multiple lesions und all S. aureus isolates obtained should be screened for ET-production to prevent false-negative results. Lysotyping alone gives no proof of ET-production since types II 55/71 and II 3A/3C do not produce ET in all cases and toxinogenic S. aureus strains of phage groups I and III have been described.

Enzyme-linked immunosorbent assays for Staphylococcus aureus exfoliative toxins A and B and some applications

Two enzyme-linked immunosorbent assays were developed for detection of staphylococcal exfoliative toxins A and B (ETA and ETB) with a double-antibody sandwich protocol. Antibodies against both toxins were purified by affinity chromatography from sheep antisera raised against purified ETA and ETB. These affinity-purified antibodies were free of detectable amounts of antibodies to other staphylococcal antigens and neutralized the actions of ETA and ETB. Alkaline phosphatase was conjugated to these antibodies. The enzyme-linked immunosorbent assay, which could detect at least 3 ng of ETA and ETB per ml, was used to quantitate the toxins in the culture supernatant fluids of staphylococcal strains. Thus, the kinetics of ETA and ETB synthesis and of ETA and ETB release into the supernatant fluids were determined; other determinations included the roles of carbon dioxide concentration, pH, glucose concentration, temperature, and agitation on the production of ETA and ETB.

[Demonstration by electrosyneresis of 2 exfoliation serotypes produced by Staphylococcus aureus]

The method described allowed a rapid, easy and reliable detection of exfoliative toxin produced by Staphylococcus aureus. A new culture technique of S. aureus strains and the detection of exfoliative toxin by electrosyneresis are described. This could replace the new-born mouse test. Such a method was useful for epidemiological studies because a lot of strains of S. aureus could be screened for exfoliative toxin production; thus the serotype of the toxin (ETA or ETB) was also determined.

[Exfoliatin in neonatal staphylococcal infections]

An outbreak of staphylococcal skin infection in neonates was investigated clinically, bacteriologically and epidemiologically with the following findings: (1) In 8 out of 13 cases, exfoliatin-producing staphylococci were present in the bullae, which is unusual with bullous lesions occurring at other ages; (2) exfoliatin producing staphylococci were present in all children with bullous lesions, as well as in carriers; (3) 39% of the phage II group staphylococci studied produced exfoliatin; (4) purulent lesions due to phage II staphylococci which did not produce exfoliatin were observed. The contaminating agent could be identified in most cases.

[Prevalence of exfoliatin-producing strains in phage group II "Staphylococcus aureus" (author's transl)]

Prevalence of exfoliatin production has been investigated in 100 strains of Staphylococcus aureus, bacteriophage group II, by inoculation into newborn mice. Serotyping, detection of protein A and antibiotic susceptibility tests have also been performed. Thirty-one strains (31%) were toxin producers; they all produced a yellow pigment; there was no difference in phage attacks between toxinogenic and non-toxinogenic strains; but exfoliatin production was significantly associated to the presence of agglutinogens h2 and 263-2; rate of protein-A presence and of antibiotic susceptibility did not differ between the two groups of strains. In addition, toxin production has been investigated in 31 isolates from various skin lesions; 9 were found toxinogenic (8 amongst them had been cultivated from bullous lesions); most of them belonged to phage group II and possessed agglutinogens h2 and 263-2. So, in order to carry out the diagnosis of some bacterial skin infections, clinical symptoms, pathological and bacteriological data must be compared; the latter must include phage-typing, serotyping and exfoliatin detection.

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.

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.