Cloning and characterization of the gene, speC, for pyrogenic exotoxin type C from Streptococcus pyogenes

Identification of distinct impacts of CovS inactivation on the transcriptome of acapsular group A streptococci

Group A streptococcal (GAS) strains causing severe, invasive infections often have mutations in the control of virulence two-component regulatory system (CovRS) which represses capsule production, and high-level capsule production is considered critical to the GAS hypervirulent phenotype. Additionally, based on studies in emm1 GAS, hyperencapsulation is thought to limit transmission of CovRS-mutated strains by reducing GAS adherence to mucosal surfaces. It has recently been identified that about 30% of invasive GAS strains lacks capsule, but there are limited data regarding the impact of CovS inactivation in such acapsular strains. Using publicly available complete genomes (n = 2,455) of invasive GAS strains, we identified similar rates of CovRS inactivation and limited evidence for transmission of CovRS-mutated isolates for both encapsulated and acapsular emm types. Relative to encapsulated GAS, CovS transcriptomes of the prevalent acapsular emm types emm28, emm87, and emm89 revealed unique impacts such as increased transcript levels of genes in the emm/mga region along with decreased transcript levels of pilus operon-encoding genes and the streptokinase-encoding gene ska. CovS inactivation in emm87 and emm89 strains, but not emm28, increased GAS survival in human blood. Moreover, CovS inactivation in acapsular GAS reduced adherence to host epithelial cells. These data suggest that the hypervirulence induced by CovS inactivation in acapsular GAS follows distinct pathways from the better studied encapsulated strains and that factors other than hyperencapsulation may account for the lack of transmission of CovRS-mutated strains. IMPORTANCE Devastating infections due to group A streptococci (GAS) tend to occur sporadically and are often caused by strains that contain mutations in the control of virulence regulatory system (CovRS). In well-studied emm1 GAS, the increased production of capsule induced by CovRS mutation is considered key to both hypervirulence and limited transmissibility by interfering with proteins that mediate attachment to eukaryotic cells. Herein, we show that the rates of covRS mutations and genetic clustering of CovRS-mutated isolates are independent of capsule status. Moreover, we found that CovS inactivation in multiple acapsular GAS emm types results in dramatically altered transcript levels of a diverse array of cell-surface protein-encoding genes and a unique transcriptome relative to encapsulated GAS. These data provide new insights into how a major human pathogen achieves hypervirulence and indicate that factors other than hyperencapsulation likely account for the sporadic nature of the severe GAS disease.

Agr Regulation of Streptococcal Pyrogenic Exotoxin A in Staphylococcus aureus

Group A streptococcal pyrogenic exotoxins (SPEs A, B, and C) are superantigens. SPE A shares high sequence similarity with Staphylococcus aureus enterotoxins (SEs) B and C. Since SPE A is bacteriophage-encoded, we hypothesized that its gene ( speA ) was acquired from S. aureus . speA , when cloned into S. aureus , was stably expressed, its protein resistant to proteases, and the gene under accessory gene regulator control. speA was acquired by streptococci from cross-species transduction. speB was not expressed in S. aureus. SPE C was degraded by staphylococcal proteases. The genes speB and speC were not recently acquired from S. aureus.

Antibodies to the conserved region of the M protein and a streptococcal superantigen cooperatively resolve toxic shock-like syndrome in HLA-humanized mice

Invasive streptococcal disease (ISD) and toxic shock syndrome (STSS) result in over 160,000 deaths each year. We modelled these in HLA-transgenic mice infected with a clinically lethal isolate expressing Streptococcal pyrogenic exotoxin (Spe) C and demonstrate that both SpeC and streptococcal M protein, acting cooperatively, are required for disease. Vaccination with a conserved M protein peptide, J8, protects against STSS by causing a dramatic reduction in bacterial burden associated with the absence of SpeC and inflammatory cytokines in the blood. Furthermore, passive immunotherapy with antibodies to J8 quickly resolves established disease by clearing the infection and ablating the inflammatory activity of the M protein, which is further enhanced by addition of SpeC antibodies. Analysis of 77 recent isolates of Streptococcus pyogenes causing ISD, demonstrated that anti-J8 antibodies theoretically recognize at least 73, providing strong support for using antibodies to J8, with or without antibodies to SpeC, as a therapeutic approach.

The role of the MHC on resistance to group a streptococci in mice

The severity of infection with Streptococcus pyogenes is strongly influenced by the host's genetics. This observation extends to the murine model of streptococcal infection, where the background of the mouse strain determines the infection outcome (BALB/c are resistant, whereas C3H/HeN are susceptible). To determine the extent to which the MHC complex (H2) contributed to diseases susceptibility, the response to S. pyogenes of congenic BALB mice from a resistant background (BALB/c), but carrying the H2(k) region of susceptible C3H/HeN mice (BALB/k), was examined. BALB/k were as susceptible as the H2 donor strain (C3H/HeN). Linkage analysis performed in F(2) backcross ([BALB/c x C3H/HeN] x BALB/c) mice confirmed the presence of a susceptibility locus within the H2 region on proximal chromosome 17. The possibility that modulation of T cell responses to streptococcal superantigens (GAS-SAgs) by different H2 haplotypes may influence disease severity was examined. BALB/k exhibited a significantly stronger response at the level of cell proliferation and cytokine production to GAS-SAgs than did BALB/c mice. However, the fact that T cell-deficient SCID-C3H/HeN mice also exhibited a susceptible phenotype suggests a more important contribution of innate effector cells to disease susceptibility. Lower transcriptional levels of certain inflammation-related regulatory genes located on chromosome 17 were detected in macrophages from susceptible than in those from resistant mice in response to infection. These results suggest that susceptibility to S. pyogenes may be associated with an altered transcription of specific genes that may compromise the endogenous regulatory processes controlling the inflammatory cascade and favor the progression to sepsis.

Site-specific manifestations of invasive group a streptococcal disease: type distribution and corresponding patterns of virulence determinants

As part of a national surveillance program on invasive group A streptococci (GAS), isolates that caused specific manifestations of invasive GAS disease in The Netherlands were collected between 1992 and 1996. These site-specific GAS infections involved meningitis, arthritis, necrotizing fasciitis, and puerperal sepsis. An evaluation was performed to determine whether GAS virulence factors correlate with these different disease manifestations. PCRs were developed to detect 9 genes encoding exotoxins and 12 genes encoding fibronectin binding proteins. The genetic backgrounds of all isolates were determined by M genotyping and pulsed-field gel electrophoresis (PFGE) analysis. The predominant M types included M1, M2, M3, M4, M6, M9, M12, and M28. Most M types were associated with all manifestations of GAS disease. However, M2 was found exclusively in patients with puerperal sepsis, M6 predominated in patients with meningitis, and M12 predominated in patients with GAS arthritis. While characteristic gene profiles were detected in most M types, the resolution of detection of different gene profiles within M genotypes was enhanced by PFGE analysis, which clearly demonstrated the existence of some clonal lineages among invasive GAS isolates in The Netherlands. M1 isolates comprised a single clone carrying highly mitogenic toxin genes (speA, smeZ) and were associated with toxic shock-like syndrome. Toxin profiles were highly conserved among the most virulent strains, such as M1 and M3.

The fundamental contribution of phages to GAS evolution, genome diversification and strain emergence

The human bacterial pathogen group A Streptococcus (GAS) causes many different diseases including pharyngitis, tonsillitis, impetigo, scarlet fever, streptococcal toxic shock syndrome, necrotizing fasciitis and myositis, and the post-infection sequelae glomerulonephritis and rheumatic fever. The frequency and severity of GAS infections increased in the 1980s and 1990s, but the cause of this increase is unknown. Recently, genome sequencing of serotype M1, M3 and M18 strains revealed many new proven or putative virulence factors that are encoded by phages or phage-like elements. Importantly, these genetic elements account for an unexpectedly large proportion of the difference in gene content between the three strains. These new genome-sequencing studies have provided evidence that temporally and geographically distinct epidemics, and the complex array of GAS clinical presentations, might be related in part to the acquisition or evolution of phage-encoded virulence factors. We anticipate that new phage-encoded virulence factors will be identified by sequencing the genomes of additional GAS strains, including organisms non-randomly associated with particular clinical syndromes.

Immunological and biochemical characterization of streptococcal pyrogenic exotoxins I and J (SPE-I and SPE-J) from Streptococcus pyogenes

Recently, we described the identification of novel streptococcal superantigens (SAgs) by mining the Streptococcus pyogenes M1 genome database at Oklahoma University. Here, we report the cloning, expression, and functional analysis of streptococcal pyrogenic exotoxin (SPE)-J and another novel SAg (SPE-I). SPE-I is most closely related to SPE-H and staphylococcal enterotoxin I, whereas SPE-J is most closely related to SPE-C. Recombinant forms of SPE-I and SPE-J were mitogenic for PBL, both reaching half maximum responses at 0.1 pg/ml. Evidence from binding studies and cell aggregation assays using a human B-lymphoblastoid cell line (LG-2) suggests that both toxins exclusively bind to the polymorphic MHC class II beta-chain in a zinc-dependent mode but not to the generic MHC class II alpha-chain. The results from analysis by light scattering indicate that SPE-J exists as a dimer in solution above concentrations of 4.0 mg/ml. Moreover, SPE-J induced a rapid homotypic aggregation of LG-2 cells, suggesting that this toxin might cross-link MHC class II molecules on the cell surface by building tetramers of the type HLA-DRbeta-SPE-J-SPE-J-HLA-DRbeta. SPE-I preferably stimulates T cells bearing the Vbeta18.1 TCR, which is not targeted by any other known SAG: SPE-J almost exclusively stimulates Vbeta2.1 T cells, a Vbeta that is targeted by several other streptococcal SAgs, suggesting a specific role for this T cell subpopulation in immune defense. Despite a primary sequence diversity of 51%, SPE-J is functionally indistinguishable from SPE-C and might play a role in streptococcal disease, which has previously been addressed to SPE-C.

Streptococcal pyrogenic exotoxin F (SpeF) causes permeabilization of lung blood vessels

Acute respiration distress syndrome (ARDS) is a typical complication in toxic shock-like syndrome (TSLS) caused by Streptococcus pyogenes. An isolated perfused rat lung model was used to identify the causative agent of ARDS in TSLS in this study. Some crude preparations separated from the culture supernatants of S. pyogenes isolates caused rapid increases in the weight of perfused lungs, indicating vascular permeabilization. Six samples from M type 1 and 3 isolates from TSLS and pharyngitis patients showed strong permeabilization activity, whereas preparations from isolates of other M types (although the number of isolates examined was limited) were negative. The active substance was purified to a single band by sodium dodecyl sulfate-polyacrylamide gel electrophoresis using various columns, and the N-terminal amino acid sequence was determined. The resultant sequence of eight amino acids was identical to SpeF (mitogenic factor). Moreover, the vascular permeabilization activity of the purified band was abolished with anti-SpeF antiserum prepared by immunizing with the purified SpeF. This activity was also neutralized by the antiserum prepared by immunizing with a synthetic peptide derived from the published SpeF sequence. These results suggested that streptococcal SpeF is a major cause of permeabilization of lung blood vessels and sufficient for the pathogenesis of ARDS under the conditions of TSLS caused by S. pyogenes.

Identification and characterization of novel superantigens from Streptococcus pyogenes

Three novel streptococcal superantigen genes (spe-g, spe-h, and spe-j) were identified from the Streptococcus pyogenes M1 genomic database at the University of Oklahoma. A fourth novel gene (smez-2) was isolated from the S. pyogenes strain 2035, based on sequence homology to the streptococcal mitogenic exotoxin z (smez) gene. SMEZ-2, SPE-G, and SPE-J are most closely related to SMEZ and streptococcal pyrogenic exotoxin (SPE)-C, whereas SPE-H is most similar to the staphylococcal toxins than to any other streptococcal toxin. Recombinant (r)SMEZ, rSMEZ-2, rSPE-G, and rSPE-H were mitogenic for human peripheral blood lymphocytes with half-maximal responses between 0.02 and 50 pg/ml (rSMEZ-2 and rSPE-H, respectively). SMEZ-2 is the most potent superantigen (SAg) discovered thus far. All toxins, except rSPE-G, were active on murine T cells, but with reduced potency. Binding to a human B-lymphoblastoid line was shown to be zinc dependent with high binding affinity of 15-65 nM. Evidence from modeled protein structures and competitive binding experiments suggest that high affinity binding of each toxin is to the major histocompatibility complex class II beta chain. Competition for binding between toxins was varied and revealed overlapping but discrete binding to subsets of class II molecules in the hierarchical order (SMEZ, SPE-C) > SMEZ-2 > SPE-H > SPE-G. The most common targets for the novel SAgs were human Vbeta2.1- and Vbeta4-expressing T cells. This might reflect a specific role for this subset of Vbetas in the immune defense of gram-positive bacteria.

Age-related occurrence of inhibitory antibodies to streptococcal pyrogenic superantigens

Several bacteria, such as staphylococci and streptococci, can produce superantigens (SA) that induce the activation of T cells in humans. Although these organisms are the major causes of infection in children, the evidence that T cells are vigorously activated by SA produced by such organisms has not been reported except for toxic shock syndrome. In a previous paper, we demonstrated that inhibitory IgG antibodies (Ab) to SA in humans may protect against SA stimulation. In the present study, we investigated the occurrence of these inhibitory Ab to SA in 94 healthy children by the enzyme linked immunosorbent assay technique and the suppressive effect on T cell stimulation by SA. The positivity of Ab to streptococcal pyrogenic exotoxin (SPE)-A, SPE-C and staphylococcal enterotoxin B (SEB) increased with age. The age at which more than 50% of children exhibited Ab to SA was 1 year for SEB, 6 years for SPE-C and 11 years for SPE-A. Sera from these children were inhibitory to T cell proliferation elicited by SA in proportion to the concentration of IgG Ab to each SA. Sera supplemented with IgG Ab to SA by gamma-globulin therapy became inhibitory to T cell proliferation by SA. We conclude that, as children grow, they can develop Ab to SA that may play a role in protecting them against vigorous T cell activation by SA.

Erythrogenic toxin type A (ETA): epidemiological analysis of gene distribution and protein formation in clinical Streptococcus pyogenes strains causing scarlet fever and the streptococcal toxic shock-like syndrome (TSLS)

Erythrogenic toxin type A (ETA) is assumed to play a causative role in both scarlet fever and the streptococcal toxic shock-like syndrome (TSLS). For a molecular epidemiological analysis of the gene of erythrogenic toxin type A (speA) we used altogether 497 clinical isolates of Streptococcus pyogenes belonging to three groups: a) isolates from patients with scarlet fever, b) isolates from cases with TSLS, c) isolates from patients with other streptococcal infections (like otitis media, tonsillitis, impetigo) (general group). We found that less than 50% of the scarlet fever-associated strains possessed the speA gene as compared to 25% of the general group. Only 5 to 30% of these strains secreted the toxin under experimental conditions in very low quantities. Among strains isolated from TSLS, 67% appeared to contain the speA gene. The amount of ETA secreted into the medium was also extremely low. Southern hybridization patterns proved to be the same with an speA-specific probe in all three groups of streptococcal isolates (HaeIII, HindIII). Increased occurrence of the speA gene among scarlet fever and TSLS-associated strains does not seem to be sufficient to support the hypothesis that ETA may have a causative role in both diseases since a considerable number of strains in these groups did not possess the speA gene.

Erythrogenic toxins A, B and C: occurrence of the genes and exotoxin formation from clinical Streptococcus pyogenes strains associated with streptococcal toxic shock-like syndrome

We report the study of 53 clinical isolates of group A streptococci, all from patients with streptococcal toxic shock-like syndrome. The strains were analysed for the occurrence of the genes of erythrogenic toxins (pyrogenic exotoxins) types A, B and C and in vitro production of these toxins. In contrast to reports indicating that 85% of the toxic shock-like syndrome-associated isolates contained the erythrogenic toxin A gene, only 58.5% of our strains harboured this gene. The erythrogenic toxin C gene was detected in 22.6% of the isolates. Erythrogenic toxin A and erythrogenic toxin B were produced by 68.7% and 58.3% of the strains containing either gene. For all group A streptococci, irrespective of clinical association, the erythrogenic toxin B gene was detected in all the isolates tested. Thus, it is difficult to define a specific role for erythrogenic toxin B in toxic shock-like syndrome as there was no clear correlation between this disease and the presence of toxin genes. Our results suggest the existence of other pathogenic factor(s) produced by group A streptococci which may stimulate human peripheral T lymphocytes in a manner similar to that of erythrogenic toxins, thus explaining different observations in previous epidemiological genetic studies.

Emergence of invasive group A streptococcal disease among young children

Eight cases of invasive group A streptococcal disease in young children were reported over a three-month period, February to April 1990. The spectrum of clinical disease included: pneumonia with bacteremia (two patients), osteomyelitis/septic arthritis (three patients), epiglottitis/supraglottitis (two patients), and sepsis without a focus (one patient). Three cases followed chicken pox. Three children were in shock at the time of presentation, including one child who had a toxic shock-like appearance. Only four children had pharyngitis. Bacteremia was confirmed in three children and presumed in another three. All the subjects survived. Four isolates of group A streptococci were tested for exotoxin A, B, and C (A-0, B-4, C-1) production. These data confirm the reappearance of a highly invasive strain of group A streptococci capable of producing a variety of clinical diseases, including bacteremia and shock, in a significant proportion of victims.

Production of pyrogenic exotoxins in group A streptococci isolated from patients in Zagreb, Croatia

The pyrogenic exotoxin profiles were determined of group A streptococci isolated from patients in Zagreb, Croatia in the period 1989-1990. A total of 12 strains were studied, five from patients with serious infections and seven from patients with uncomplicated infections. Serotypes M1 and M3 were found in seven (58%) patients. Seven strains produced exotoxin A and ten strains exotoxin B. The proportion of exotoxin A and B producing strains in patients with severe infections (3 patients respectively) was similar to that found in patients with uncomplicated infections (4 and 7 patients respectively).

Molecular analysis of pyrogenic exotoxins from Streptococcus pyogenes isolates associated with toxic shock-like syndrome

Toxic shock-like syndrome (TSLS) is characterized by hypotension or shock, fever, multiorgan system involvement, and a concurrent group A streptococcal infection. We analyzed 34 streptococcal strains isolated from patients with clinically well-documented TSLS for their pyrogenic toxin profiles and M-protein types. Although strains of nine different M types were represented in the sample, 74% of the isolates were of either M type 1 or 3. It was determined that 53% produced streptococcal pyrogenic exotoxin type A under in vitro growth conditions and that 85% contained the gene encoding this toxin. These values are in contrast to the published value of 15% for the incidence of this gene in a sample of general group A streptococcal isolates. As has been found with all group A streptococci examined to date, regardless of disease association, 100% of TSLS-associated isolates contained the gene encoding pyrogenic exotoxin type B. This toxin was detectably produced by 59% of isolates. The gene encoding pyrogenic toxin type C was found in only 21% of isolates. We conclude that the pyrogenic exotoxin type A gene is associated with group A streptococcal strains isolated from patients with TSLS and may play a causative role in this illness. However, other factors are also likely to be important, since not all strains from patients with TSLS contained the A toxin gene.

Streptococcus pyogenes causing toxic-shock-like syndrome and other invasive diseases: clonal diversity and pyrogenic exotoxin expression

Genetic diversity and relationships among 108 isolates of the bacterium Streptococcus pyogenes recently recovered from patients in the United States with toxic-shock-like syndrome or other invasive diseases were estimated by multilocus enzyme electrophoresis. Thirty-three electrophoretic types (ETs), representing distinctive multilocus clonal genotypes, were identified, but nearly half the disease episodes, including more than two-thirds of the cases of toxic-shock-like syndrome, were caused by strains of two related clones (ET 1 and ET 2). These two clones were also represented by recent pathogenic European isolates. A previous report of a relatively high frequency of expression of exotoxin A among isolates recovered from toxic-shock-like syndrome patients in the United States was confirmed; and the demonstration of this association both within clones and among distantly related clones supports the hypothesis that exotoxin A is a causal factor in pathogenesis of this disease. Near identity of the nucleotide sequences of the exotoxin A structural gene of six isolates of five ETs in diverse phylogenetic lineages was interpreted as evidence that the gene has been horizontally distributed among clones, presumably by bacteriophage-mediated transfer.

Staphylococcal and streptococcal pyrogenic toxins involved in toxic shock syndrome and related illnesses

Toxic-shock syndrome (TSS) is an acute onset, multiorgan illness which resembles severe scarlet fever. The illness is caused by Staphylococcus aureus strains that express TSS toxin-1 (TSST-1), enterotoxin B, or enterotoxin C. TSST-1 is associated with menstrual TSS and approximately one-half of nonmenstrual cases; the other two toxins cause nonmenstrual cases, 47% and 3%, respectively. The three toxins are expressed in culture media under similar environmental conditions. These conditions may explain the association of certain tampons with menstrual TSS. Biochemically, the toxins are all relatively low molecular weight and fairly heat and protease stable. Enterotoxins B and C, share nearly 50% sequence homology with streptococcal scarlet fever toxin A; they share no homology with TSST-1 despite sharing numerous biological properties. Numerous animal models for development of TSS have suggested mechanisms of toxin action, though the exact molecular action is not known. The toxins are all potent pyrogens, induce T lymphocyte proliferation, requiring interleukin 1 release from macrophages, suppress immunoglobulin production, enhance endotoxin shock, and enhance hypersensitivity skin reactions. The genetic control of the toxins has been studied and suggests the exotoxins are variable traits. Some additional properties of TSS S. aureus which facilitate disease causation have been clarified.

Molecular epidemiologic analysis of the type A streptococcal exotoxin (erythrogenic toxin) gene (speA) in clinical Streptococcus pyogenes strains

A molecular epidemiology analysis was performed with over 440 clinical isolates of Streptococcus pyogenes obtained from 11 different countries in order to determine the frequency of occurrence of the type A streptococcal exotoxin (erythrogenic toxin) gene (speA) among group A strains. The colony hybridization technique employing a specific internal fragment of the speA gene was used for initial screening, and all positive results were further confirmed by the Southern hybridization technique. Among over 300 general strains obtained from patients with a variety of diseases, except scarlet fever (such as tonsillitis, impetigo, cellulitis, pyoderma, abscess, rheumatic fever, and glomerulonephritis), 15% were found to contain the speA gene. Among a group of 146 strains obtained from individuals described as having scarlet fever, 45% were shown to contain the speA gene. Further analysis of the data indicated that strains with certain M- or T-type surface antigens showed a higher (such as M and T types 1 and 3/13) or lower (such as M2, M12, T4, T5, and T28) tendency to contain the speA gene. No correlation was found between speA content of a strain and the ability to cause a specific disease, although strains possessing the speA gene were more likely to be associated with scarlet fever and rheumatic fever than with other types of disease.

Group A streptococcal pyrogenic exotoxin (scarlet fever toxin) type A and blastogen A are the same protein

Group A streptococcal pyrogenic exotoxins A, B, and C (also known as scarlet fever toxins and erythrogenic toxins) were evaluated for relatedness to another streptococcus-derived lymphocyte mitogen, blastogen A. Streptococcal pyrogenic exotoxin A and blastogen A were immunologically cross-reactive and shared the same molecular weight, N-terminal amino acid sequence, and capacity to stimulate rabbit splenocyte proliferation nonspecifically.

Bacteriophage association of streptococcal pyrogenic exotoxin type C

A gene encoding streptococcal pyrogenic exotoxin type C (SPE C) was isolated from bacteriophage DNA derived from Streptococcus pyogenes CS112. The gene, designated speC2, was shown to reside near the phage attachment site of phage CS112. A restriction endonuclease map of the CS112 phage was generated, and the location and orientation of the speC2 gene were determined. Hybridization analyses of eight SPE C-producing strains revealed restriction fragment length polymorphism of the speC gene-containing DNA fragments and further showed that each speC was linked to a common CS112 phage-derived DNA fragment.

Biological and immunological properties of the carboxyl terminus of staphylococcal enterotoxin C1

Comparisons of recently published primary sequences of staphylococcal and streptococcal pyrogenic toxins prompted an evaluation of biological and immunological properties of the C terminus of staphylococcal enterotoxin C1. The 59 N-terminal amino acids were deleted from the toxin by digestion with trypsin. The resulting fragment (Mr, 20,659) contained the remaining 180 C-terminal residues. This fragment (Trp F1) consisted of two polypeptide chains (Trp F1a and Trp F1b) linked by cysteine residues. Trp F1 was mitogenic, pyrogenic, and enhanced susceptibility of rabbits to lethal endotoxin shock. In addition, this fragment contained at least one antigenic epitope that cross-reacted with enterotoxin B.

Nucleotide sequence of streptococcal pyrogenic exotoxin type C

The nucleotide sequence of the gene speC, encoding streptococcal pyrogenic exotoxin type C (SPE C), was determined. The gene encoded a mature protein of 208 amino acids, with a calculated molecular weight of 24,354. The mature amino acid sequence of SPE C was analyzed for homology with the amino acid sequences of streptococcal pyrogenic exotoxin type A, the staphylococcal enterotoxins, and toxic shock syndrome toxin-1. Of these, SPE C shared the greatest amount of homology with streptococcal exotoxin type A.