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

Clinical manifestations of staphylococcal scalded-skin syndrome depend on serotypes of exfoliative toxins

We sought a possible correlation between the clinical manifestations of staphylococcal scalded-skin syndrome (SSSS) and the serotype of exfoliative toxins (ET) by PCR screening of the eta and etb genes in Staphylococcus aureus strains isolated from 103 patients with generalized SSSS and 95 patients with bullous impetigo. The eta gene and the etb gene were detected in, respectively, 31 (30%) and 20 (19%) episodes of generalized SSSS and 57 (60%) and 5 (5%) episodes of bullous impetigo. Both genes were detected in 52 (50%) episodes of generalized SSS and 33 (35%) episodes of bullous impetigo. To explain this link between etb and generalized SSSS, we examined the distribution of ETA- and ETB-specific antibodies in the healthy population (n = 175) and found that the anti-ETB antibody titer was lower than the anti-ETA titer. Thus, ETA is associated with bullous impetigo and ETB is associated with generalized SSSS, possibly owing to a lower titer of anti-ETB neutralizing antibodies in the general population.

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.

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.

Rapid identification by polymerase chain reaction of staphylococcal exfoliative toxin serotype A and B genes

A new system was designed to detect staphylococcal exfoliative toxin A (ETA) and B (ETB) genes by the polymerase chain reaction (PCR). The primer pairs for the ETA gene (eta) were 20 and 20-mer, and its PCR product was a 741-bp eta fragment, while the primer pairs for the ETB gene (etb) were also 20 and 20-mer, and its PCR product was a 629-bp etb fragment. When these primers were simultaneously used in the PCR, the two types of ET were clearly detected as two bands in an ETA and ETB double-producer using only one colony within 3 hr. We examined 66 strains of Staphylococcus aureus isolated from patients with staphylococcal scalded skin syndrome (SSSS) and compared the results obtained by ELISA and PCR. The same results were obtained for 56 of the strains, i.e., 30 strains were ETA producers, 20 strains were ETB producers, and 6 strains were double-producers. However, positive results were obtained for 5 of the 10 non-ET-producing strains. Two of these strains were judged by PCR as ETA producers and three as ETB producers. Thus, PCR is very sensitive and rapid in detecting ETA and ETB gene fragments in colonies isolated from patients with SSSS.

Staphylococcal scalded skin syndrome in adults. A clinical review illustrated with a new case

Staphylococcal scalded skin syndrome is rarely observed in adults; only 32 cases have been reported. In contrast to infant cases, the mortality rate is high. Two major risk factors have been identified: kidney failure and immunosuppression. In adults, clinical features are similar to those of the typical pediatric disease, but blood cultures are often positive for Staphylococcus aureus. Detection of the exfoliative toxin is required for diagnosis; the newborn mouse bioassay is, therefore, usually performed. New immunologic methods allow precise characterization of the toxins and oligonucleotide probes can be used for rapid detection of toxigenic strains. We report a case of staphylococcal scalded skin syndrome in an immunocompetent adult in whom blood cultures were positive; this is the first case in which both exfoliative toxins A and B have been identified in an adult.

Functional evidence that the Ser-195 residue of staphylococcal exfoliative toxin A is essential for biological activity

The substitution of the serine 195 residue of staphylococcal exfoliative toxin A by a cysteine residue led to a biologically inactive protein. This result is consistent with the hypothesis that exfoliative toxin A could be a protease or a lipase. However, no protease or lipase activity was detected with the native toxin.

Action of staphylococcal exfoliative toxins on epidermal cell cultures and organotypic skin

In the staphylococcal scalded skin syndrome, spontaneous intraepithelial cleavages are due to the exfoliative toxins A or B (ETA or ETB). Until now, these toxins have been studied either on epidermis or on organotypic skin cultures. In the present study, we compare the effects of these toxins on human keratinocyte cell cultures to those on human and mouse organotypic skin cultures. With concentrations of ETA or ETB of 1 mg/ml for 3 hours, spontaneous intraepithelial cleavages were noted in both cell and organotypic cultures. Keratinocyte cell cultures were as sensitive as organotypic skin cultures to these toxins. Since keratohyaline granules may represent a possible binding site for ETA or ETB, we tried to correlate the expression of keratohyaline granules with the appearance of intraepithelial clefts due to the toxins. However, when cultured in liquid medium, epithelia were not differentiated enough to allow the detection of the binding site of ETA-ETB.

Rapid screening for Staphylococcus aureus infection by measuring enterotoxin B

We developed a simple, sensitive laser nephelometric assay (LNA) to detect circulating staphylococcal enterotoxin B (SEB). This assay yields the result within 2 h and needs no special treatment. Influence of protein A, a product generated by Staphylococcus aureus, was negligible in this assay. The levels of SEB in plasma were measured in 28 patients with and without S. aureus infection with the LNA. The levels of SEB in plasma increased significantly in patients with S. aureus infection. We also demonstrated that the levels of SEB in plasma were higher in patients with methicillin-resistant S. aureus infection than in patients with nonresistant staphylococcal infection. Our data indicate that LNA is a useful assay in the early diagnosis of methicillin-resistant S. aureus infection.

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.