Cloning, characterization and overexpression of a Streptococcus pyogenes gene encoding a new type of mitogenic factor

Close Correlation of Streptococcal DNase B (sdaB) Alleles withemmGenotypes inStreptococcus pyogenes

DNase B is a major nuclease and a possible virulence factor in Streptococcus pyogenes. The allelic diversity of streptococcal DNase B (sdaB) gene was investigated in 83 strains with 14 emm genotypes. Of the 15 alleles identified, 11 alleles carried only synonymous nucleotide substitutions. On the other hand, 4 alleles had a non-synonymous substitution other than synonymous substitutions, resulting in the substitution of a single amino acid. The distribution of each allele was generally emm genotype-specific. Only sdaB7 was found in both emm2 and emm4. The promoter region was highly conserved and DNase B protein was similarly expressed in all alleles.

Selection of indicators for tonsillectomy in adults with recurrent tonsillitis

BACKGROUND

We aimed to find some new indicators for tonsillectomy (TE) in adults with recurrent tonsillitis (RT) by exploring whether the frequency of tonsillitis episodes and the length of morbidity period are associated with the macroscopic signs of sclerotic process in tonsils and microbiological data assessed by culture, molecular (PCR) and transmission electron microscopy (EM) methods.

METHODS

The study involved 62 RT patients admitted for TE (age range 15-35, median 22 years) and 54 healthy volunteers (age range 18-24, median 20 years). The index of tonsillitis (IT) was calculated by multiplying the number of tonsillitis episodes per year by the morbidity period in years. On oropharyngeal examination the presence or absence of three sclerotic signs was evaluated: tonsillar sclerosis, obstruction of tonsillar crypts and scar tissue on the tonsils. The occurrence of Streptococcus pyogenes was assessed by culture and PCR methods in 24 tonsillar core specimens. The samples for EM investigation of crypt epithelium were taken from 10 removed tonsils.

RESULTS

The IT values were in positive correlation with the number of sclerotic signs on oropharyngeal examination (r = 0.325, P = 0.010). Based on the IT values and the presence or absence of tonsillar sclerosis and obstruction of tonsillar crypts the receiver-operating curve (ROC) was constructed. It revealed that an IT score of 36 is an optimal cut-off value for prediction of sclerotic type tonsils. S. pyogenes was never found by culture, but its presence by PCR in nearly one third (29%) of diseased tonsillar tissue specimens was tightly associated with longer morbidity. EM revealed coccoid forms of intracellular bacteria in the crypt epithelium, which was accompanied with the damage of tight junctions between epithelial cells.

CONCLUSION

The index of tonsillitis > or = 36, being a combination between the frequency of tonsillitis and the length of morbidity period, predicts the sclerotic process in recurrently inflamed tonsils. Therefore, the high IT values could serve as an indicator for TE in adults. The correlation between the longer morbidity period and the presence of S. pyogenes by PCR suggests that persistent infection may have a role in maintenance of recurrent inflammation in tonsils.

Post-proteomic identification of a novel phage-encoded streptodornase, Sda1, in invasive M1T1 Streptococcus pyogenes

The M1T1 strain remains the most frequently isolated strain from group A streptococcal (GAS) infection cases worldwide. We previously reported that M1T1 differs from the fully sequenced M1 SF370 strain. To better understand the reason for the persistence and increased virulence of M1T1, we analysed its secreted proteome and identified two virulence proteins that are not present in the sequenced M1 SF370 strain: streptococcal pyrogenic exotoxin A (SpeA) and a streptodornase D (SdaD) homologue. In the present study, we determined the nucleotide sequence of the M1T1 streptodornase and found that its deduced amino acid sequence is highly similar to other streptococcal streptodornases, and is most closely related to the SdaD of GAS strain M49. M1T1 Sda shares two highly conserved domains with several DNases and putative DNases in streptococci; however, it possesses a unique C-terminal amino acid sequence. Thus, we named the protein Sda1, and we detected the presence of the sda1 gene in 16 M1T1 clinical isolates. The cloned and expressed Sda1 degrades both streptococcal and mammalian DNA at physiological pH. Amino acid similarity analyses of known GAS deoxyribonucleases suggest that Sda1 may be a chimeric protein created through recombination events. Moreover, a natural mutation that resulted in longer Sda1 and SdaD as compared to other GAS DNases was found to confer increased activity on the protein. Analysis of the sequences flanking sda1 determined that it is carried by a prophage or a prophage-like element inserted in the tRNA-Ser gene of M1T1 GAS. Ongoing studies in our laboratory aim to determine the contribution of Sda1 to the virulence of this globally disseminated M1T1 strain.

Fatal case of toxic shock-like syndrome due to group C streptococcus associated with superantigen exotoxin

Group C streptococci have been reported to cause invasive disease similar to that classically associated with group A streptococcus (GAS). We describe a fatal case of toxic shock-like syndrome due to Streptococcus equi subsp. zooepidemicus. The causative organism did not possess any known GAS superantigen exotoxin genes but did show evidence of superantigen production.

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 prophage sequences of Lactobacillus plantarum strain WCFS1

The Lactobacillus plantarum commensal WCFS1 contains four prophage elements in its genome. Lp1 and Lp2 are two about 40-kb-long uninducible prophages that share closely related DNA packaging, head and tail genes defining a second lineage of pac-site Siphoviridae in L. plantarum, distinct from L. plantarum phage phig1e, but related to Bacillus phage SPP1 and Lactococcus phage TP901-1. Northern analysis revealed transcribed prophage genes exclusively near both attachment sites. Comparative genomics identified candidate lysogenic conversion genes (LCG) downstream of the lysis cassette and within the lysogeny module. Notable are genes with sequence similarities to putative LCG from Streptococcus pyogenes prophages and to a Bacillus plasmid. Both prophages harbored tRNA genes. R-Lp3 and R-Lp4 represent short prophage remnants; R-Lp3 abuts Lp2 and displays sequence links to cos-site Siphoviridae.

Association of pyrogenic exotoxin genes with pharyngitis and rheumatic fever/rheumatic heart disease among Indian isolates of Streptococcus pyogenes

AIM

To monitor the presence of various pyrogenic exotoxin genes in strains of Streptococcus pyogenes isolated in India.

METHODS & RESULTS

Isolates recovered from pharyngitis (52) and rheumatic fever (RF)/ rheumatic heart disease (RHD) (8) patients were analysed for the presence of toxin genes, speA, speB and speF, by PCR. The specificity of the products was confirmed by restriction enzyme digestion and Southern hybridization. Among the 60 isolates studied, the incidence of speA, speB and speF were 5(8.3%), 56(93.3%) and 53(88.3%), respectively. The expression of these genes was established in representative isolates by RT-PCR.

CONCLUSIONS

Comparative analysis of frequency of the speA, speB and speF genes, among pharyngitis and RF/RHD associated isolates, showed higher incidence in RF/RHD (25%, 100%,100%) as compared to pharyngitis patients (5.8%, 92.3%, 86.5%), respectively. SIGNIFICANCE OF STUDY: The presence of the speA gene, which is usually associated with scarlet fever or toxic shock-like syndrome, within few Indian isolates may be indicative of new virulent strains circulating within the Indian community. High distribution of toxin genes among RF/RHD compared to pharyngitis isolates indicate their possible role in increased virulence.

Superantigen bacterial toxins: state of the art

Superantigens (SAgs) are viral and bacterial proteins exhibiting a highly potent polyclonal lymphocyte-proliferating activity for CD4(+), CD8(+) and sometimes gammadelta(+) T cells of human and (or) various animal species. Unlike conventional antigens, SAgs bind as unprocessed proteins to invariant regions of major histocompatibility complex (MHC) class II molecules on the surface of antigen-presenting cells (APCs) and to particular motifs of the variable region of the beta chain (Vbeta) of T-cell receptor (TcR) outside the antigen-binding groove. As a consequence, SAgs stimulate at nano-to picogram concentrations up to 10 to 30% of host T-cell repertoire while only one in 10(5)-10(6) T cells (0.01-0.0001%) are activated upon conventional antigenic peptide binding to TcR. SAg activation of an unusually high percentage of T lymphocytes initiates massive release of pro-inflammatory and other cytokines which play a pivotal role in the pathogenesis of the diseases provoked by SAg-producing microorganisms. We briefly describe in this review the molecular and biological properties of the bacterial superantigen toxins and mitogens identified in the past decade.

Comparative genomics reveals close genetic relationships between phages from dairy bacteria and pathogenic Streptococci: evolutionary implications for prophage-host interactions

The genome of the highly pathogenic M1 serotype Streptococcus pyogenes isolate SF370 contains eight prophage elements. Only prophage SF370.1 could be induced by mitomycin C treatment. Prophage SF370.3 showed a 33.5-kb-long genome that closely resembled the genome organization of the cos-site temperate Siphovirus r1t infecting the dairy bacterium Lactococcus lactis. The two-phage genomes shared between 60 and 70% nucleotide sequence identity over the DNA packaging, head and tail genes. Analysis of the SF370.3 genome revealed mutations in the replisome organizer gene that may prevent the induction of the prophage. The mutated phage replication gene was closely related to a virulence marker identified in recently emerged M3 serotype S. pyogenes strains in Japan. This observation suggests that prophage genes confer selective advantage to the lysogenic host. SF370.3 encodes a hyaluronidase and a DNase that may facilitate the spreading of S. pyogenes through tissue planes of its human host. Prophage SF370.2 showed a 43-kb-long genome that closely resembled the genome organization of pac-site temperate Siphoviridae infecting the dairy bacteria S. thermophilus and L. lactis. Over part of the structural genes, the similarity between SF370.2 and S. thermophilus phage O1205 extended to the nucleotide sequence level. SF370.2 showed two probable inactivating mutations: one in the replisome organizer gene and another in the gene encoding the portal protein. Prophage SF370.2 also encodes a hyaluronidase and in addition two very likely virulence factors: prophage-encoded toxins acting as superantigens that may contribute to the immune deregulation observed during invasive streptococcal infections. The superantigens are encoded between the phage lysin and the right attachment site of the prophage genome. The genes were nearly sequence identical with a DNA segment in S. equi, suggesting horizontal gene transfer. The trend for prophage genome inactivation was even more evident for the remaining five prophage sequences that showed massive losses of prophage DNA. In these prophage remnants only 13-0.3 kb of putative prophage DNA was detected. We discuss the genomics data from S. pyogenes strain SF370 within the framework of Darwinian coevolution of prophages and lysogenic bacteria and suggest elements of genetic cooperation and elements of an arms race in this host-parasite relationship.

Pyrogenicity and cytokine-inducing properties of Streptococcus pyogenes superantigens: comparative study of streptococcal mitogenic exotoxin Z and pyrogenic exotoxin A

Streptococcal mitogenic exotoxin Z (SMEZ), a superantigen derived from Streptococcus pyogenes, provoked expansion of human lymphocytes expressing the Vbeta 2, 4, 7 and 8 motifs of T-cell receptor. SMEZ was pyrogenic in rabbits and stimulated the expression of the T-cell activation markers CD69 and cutaneous lymphocyte-associated antigen. A variety of cytokines was released by human mononuclear leukocytes stimulated with SMEZ, which was 10-fold more active than streptococcal pyrogenic exotoxin A. Th2-derived cytokines were elicited only by superantigens and not by streptococcal cells.

Mitogenic factor (MF) is the major DNase of serotype M89 Streptococcus pyogenes

To investigate the role of mitogenic factor (MF) in streptococcal pathogenesis, the structural gene (mf) encoding this protein was disrupted in a clinical isolate of Streptococcus pyogenes H293, to yield the isogenic mutant H363. Growth in enriched broth and on blood agar was unaffected by disruption of mf. Cell-free broth supernatants from H293 and H363 demonstrated identical promitogenic activities when co-incubated with human peripheral blood mononuclear cells, even when diluted 100000-fold, showing that MF is not a major streptococcal mitogen compared with other secreted superantigens. Disruption of mf resulted in complete loss of DNase B production and detectable DNase activity in H363 compared with the parent strain, confirming that the single gene mf, which is present in all group A streptococcal M serotypes studied, encodes DNase B. Despite loss of DNase activity, the virulence of S. pyogenes in a mouse model of necrotizing fasciitis and myositis was unaffected.

Pathogenesis of group A streptococcal infections

Group A streptococci are model extracellular gram-positive pathogens responsible for pharyngitis, impetigo, rheumatic fever, and acute glomerulonephritis. A resurgence of invasive streptococcal diseases and rheumatic fever has appeared in outbreaks over the past 10 years, with a predominant M1 serotype as well as others identified with the outbreaks. emm (M protein) gene sequencing has changed serotyping, and new virulence genes and new virulence regulatory networks have been defined. The emm gene superfamily has expanded to include antiphagocytic molecules and immunoglobulin-binding proteins with common structural features. At least nine superantigens have been characterized, all of which may contribute to toxic streptococcal syndrome. An emerging theme is the dichotomy between skin and throat strains in their epidemiology and genetic makeup. Eleven adhesins have been reported, and surface plasmin-binding proteins have been defined. The strong resistance of the group A streptococcus to phagocytosis is related to factor H and fibrinogen binding by M protein and to disarming complement component C5a by the C5a peptidase. Molecular mimicry appears to play a role in autoimmune mechanisms involved in rheumatic fever, while nephritis strain-associated proteins may lead to immune-mediated acute glomerulonephritis. Vaccine strategies have focused on recombinant M protein and C5a peptidase vaccines, and mucosal vaccine delivery systems are under investigation.

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.

Streptococcal DNase B is immunologically identical to superantigen SpeF but involves separate domains

The previous suggestion that streptococcal superantigen SpeF might be identical to DNase B was confirmed in this study. Polyclonal SpeF-specific antisera were able to inhibit depolymerization of methyl-green DNA by DNase B. However, T-cell mitogenicity and nuclease activity appear to involve separate immune epitopes on SpeF, since sera with the capacity to neutralize the mitogenic activity of SpeF did not always inhibit the DNase activity.

Inhibition of human peripheral blood mononuclear cell proliferation by Streptococcus pyogenes cell extract is associated with arginine deiminase activity

Streptococcus pyogenes (group A Streptococcus) cell extracts (CE) have a remarkably powerful and dose-dependent inhibitory effect on antigen, superantigen, or mitogen-stimulated human peripheral blood mononuclear cell (PBMC) proliferation in vitro. Purification of the inhibitory component present in S. pyogenes type M5 (Manfredo strain) CE by anion-exchange chromatography followed by gel filtration chromatography showed that the inhibitor had an approximate native molecular mass of 100 kDa. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified inhibitory fractions followed by silver staining gave a single band with an approximate molecular mass of 47 kDa, indicating that the inhibitor is composed of two identical subunits. NH2-terminal sequencing of the protein revealed that it was identical to the previously characterized streptococcal acid glycoprotein (SAGP); this protein possesses between 31.5 and 39.0% amino acid identity with arginine deiminase (AD) from Mycoplasma hominis, Mycoplasma arginini, Pseudomonas putida, and Pseudomonas aeruginosa. AD enzyme activity was present in unfractionated CE prepared from a range of streptococcal strains, and partially purified inhibitory fractions of Manfredo CE also had high levels of activity. The inhibitory effect of Manfredo CE was overcome by the addition of L-arginine to proliferation assays in which human PBMC were stimulated with phytohemagglutinin. We conclude that SAGP, or its homolog, possesses AD activity and that the potent inhibition of proliferation of human T cells by streptococcal CE is due to activity of this enzyme.

Serologic evidence that streptococcal superantigens are not involved in the pathogenesis of Kawasaki disease

Kawasaki disease (KD) is an acute multisystem vasculitis of unknown etiology and is associated with marked activation of T cells and monocyte macrophages, leading to the assumption that superantigens are involved in its pathogenesis. To determine if an association exists between streptococcal superantigens and KD, we examined serum antibody responses to superantigens in sera from 50 paired acute and convalescent KD patients using purified recombinant streptococcal superantigens, such as SPEA, SPEC, SSA and MF. We found a very low frequency of detection of anti-superantigen antibodies by ELISA and no marked IgG seroconversion to each superantigen, indicating the absence of a serological relationship between toxin-producing streptococcal infection and the onset of KD.

Streptococcal mitogenic exotoxin Z, a novel acidic superantigenic toxin produced by a T1 strain of Streptococcus pyogenes

Streptococcus pyogenes T1 was previously found to produce an acidic mitogenic exotoxin, designated A beta, antigenically distinct from erythrogenic toxin type A (ETA) of strains T1 and NY5. Following chemical analysis and biological characterization, we have renamed this toxin streptococcal mitogenic exotoxin Z (SMEZ). Physicochemical separation of SMEZ from ETA was successfully performed on a hydrophobic chromatograph. The isoelectric point was pH 5.3, and the molecular size was estimated to be 28 kDa. These values were similar to those of ETA, but the amino acid composition and the NH2-terminal sequence of SMEZ were distinct from those of any mitogenic exotoxins hitherto described. Its mitogenic activity was found to be more potent than that of ETA in rabbit lymphocyte cultures. A specific antiserum raised against SMEZ did not cross-react with ETA, ETB, or ETC in the neutralization tests of mitogenic and erythrogenic activities. Its superantigenic nature was evident from the reverse transcriptase PCR findings of the T-cell receptor Vbeta profiles of rabbit lymphocytes stimulated in vitro. The Vbeta 8 subfamily was unique to SMEZ, while the Vbeta 2 and 6 subfamilies were found to be common among lymphocytes stimulated with ETA, ETB, ETC, or SMEZ. The results from this study provide an additional example of the diversity that exists among mitogenic or superantigenic exotoxins of streptococcal origin.

Polymerase chain reaction for Streptococcus pyogenes used to evaluate an optical immunoassay for the detection of group A streptococci in children with pharyngitis

BACKGROUND

In evaluations of sensitive rapid tests for group A streptococci such as the optical immunoassay (OIA), some samples are positive by the antigen test but negative by culture. A method is needed for resolving these discrepant results.

OBJECTIVE

To develop a PCR-based assay to detect group A streptococci and to use it to establish a reference standard for evaluating an OIA for group A streptococcal antigen.

METHODS

A PCR assay that detects a segment of the MF gene of Streptococcus pyogenes was developed for the detection of group A streptococci in throat swabs. Paired swabs were obtained from 200 children with symptomatic pharyngitis and used to perform OIA, agar culture, broth-enhanced culture and PCR. As a reference standard any patient with group A streptococci detected by either culture or PCR was considered to be truly positive.

RESULTS

In comparison to agar and broth-enhanced culture procedures, OIA had sensitivities of 82 and 80% and specificities of 87 and 89%, respectively. Eight (44%) of 18 samples that were positive by OIA but negative by culture were positive for group A streptococci by PCR. Compared with the reference standard, sensitivities were OIA 76%, agar culture 79%, broth-enhanced culture 86% and PCR 96%. The specificity of OIA was 92%.

CONCLUSIONS

PCR can be used to establish a reference standard for evaluating rapid tests for group A streptococci. With this reference standard OIA was nearly as sensitive as but less specific than agar culture for detection of group A streptococci. Maximum detection requires use of both tests.

Mitogenic factor secreted by Streptococcus pyogenes is a heat-stable nuclease requiring His122 for activity

The gene encoding a mitogenic factor, termed MF, was cloned from Streptococcus pyogenes and the recombinant MF was overexpressed in Escherichia coli. Both the natural and recombinant MF had heat-resistant nuclease activity. The nuclease activity of MF was characterized using the recombinant protein. MF showed endonuclease activity, digesting ssDNA, dsDNA and tRNA. The optimal pH for the DNase activity of MF was 9.5. The DNase activity was enhanced approximately tenfold by the simultaneous presence of two divalent cations, Mg2+ and Ca2+, compared to either alone and was inhibited by EDTA or NaCl. The heat stability of MF was biphasic; the DNase activity was heat-stable from 0 to 50 degrees C over 80 degrees C but very unstable at around 60 degrees C. DNA digested by MF possessed 5'-phosphorylated and 3'-hydroxylated termini, identical to those obtained by digestion of DNA by pancreatic deoxyribonuclease I. A mutant clone revealed that His122 was a residue essential to the nuclease activity.

Characterization of the canine type C enterotoxin produced by Staphylococcus intermedius pyoderma isolates

The type C staphylococcal enterotoxins (SECs) are a group of highly conserved proteins with substantial antigenic cross-reactivity. Although Staphylococcus intermedius and coagulase-positive species of staphylococci are reported to produce SEC and other SEs, toxins produced by species other than Staphylococcus aureus have not been previously characterized. In this study we report the molecular, biological, and immunological properties of the canine SEC (SECcanine) expressed by pathogenic isolates of S. intermedius. The mature form of SECcanine has 239 amino acid residues and a pI of 7.0. Typical of the SEs, purified SECcanine induces an emetic response in monkeys and the proliferation of T cells in a Vbeta-dependent manner. Although SECcanine has >95% sequence identity to previously described SEC variants, its sequence is most related to SEC2 and SEC3. In contrast to the sequence similarity, the Vbeta profile induced by SECcanine is typical of that induced by SEC1. This result is likely explained by the conservation of a cysteine residue at position 26 in SECcanine; residues at this position have been previously shown to determine subtype-dependent differences in T-cell receptor interactions of other SEs. Overall, these results show that superantigen toxins produced by the multiple members of the genus Staphylococcus are highly conserved in respect to biological and structural properties. Further, the frequent association of SECcanine with pyoderma in dogs supports the notion that the toxins are important for staphylococcal survival and pathogenesis.

The toxins of group A streptococcus, the flesh eating bacteria

Streptococcus pyogenes causes a wide variety of infections in individuals of all ages in most countries of the world. Because of the frequency with which these infections occur, physicians are quite familiar with the diversity of clinical presentations associated with the Group A streptococcus. Yet in the late 1980's, a severe form of streptococcal infection, the Streptococcal Toxic Shock Syndrome, emerged and has persisted for the last 10 years. This syndrome is associated with invasive soft tissue infections and the early onset of shock and organ failure. The purpose of this paper is to briefly describe the epidemiologic and clinical features of the Streptococcal Toxic Shock Syndromes and to emphasize the role that toxins produced by S. pyogenes play in the pathogenesis of this disease.

The toxic shock syndromes

Because of the frequency with which Staphylococcus aureus and Streptococcus pyogenes infections occur, physicians are quite familiar with the diversity of their clinical presentations. In the 1970s, however, shock associated with multiorgan failure was described in menstruating female patients as well as in male patients following a variety of surgical procedures, such as rhinoplasty. This previously undescribed presentation of S. aureus infection, termed staphylococcal toxic shock syndrome, was associated with unique strains of S. aureus. In the mid-1980s, the emergence of streptococcal toxic shock syndrome was heralded by several case reports describing patients with group A streptococcal infections associated with shock and organ failure. This article compares the differences in the epidemiologic, clinical, and pathophysiologic features of the toxic shock syndromes.

Definition of the mitogenic factor (MF) as a novel streptococcal superantigen that is different from streptococcal pyrogenic exotoxins A, B, and C

Human T cell activation by recombinant mitogenic factor (rMF) was investigated in comparison with that by recombinant streptococcal pyrogenic exotoxins (rSPE) A, B, and C. Recombinant MF, rSPEA, and rSPEC were mitogenic for peripheral blood mononuclear cells (PBMC), whereas rSPEB was not. Recombinant MF required only HLA-DR for the stimulation of PBMC, as determined using monoclonal antibodies (mAb) to HLA class II molecules and the mouse L cells transfected with HLA class II molecules. Recombinant SPEA and rSPEC required HLA-DR or HLA-DQ molecule. Recombinant MF selectively stimulated V beta 2, V beta 7, V beta 8, V beta 18 and V beta 21-bearing T cells, whereas rSPEA and rSPEC activated V beta 2 and V beta 6-bearing T cells as evaluated by the quantitative T cell receptor (TCR) analytical method. No clonality was observed in the nucleotide sequences of complementarity determining region 3 of TCR V beta in T cells responding to rMF. The profiles of cytokine production by PBMC in response to rMF, rSPEA, and rSPEC were quite similar. In summary, these results demonstrate that both HLA class II molecules and the TCR V beta required for rMF-mediated T cell activation are distinct from those required for rSPEA or rSPEC-mediated activation. Therefore, the MF is a novel streptococcal super-antigen which is different from SPEA, SPEB, and SPEC.

Physical and genetic chromosomal map of an M type 1 strain of Streptococcus pyogenes

A physical map of the chromosome of an M type 1 strain of Streptococcus pyogenes was constructed following digestion with three different restriction enzymes, SmaI, SfiI, and SgrAI, and separation and analysis of fragments by pulsed-field gel electrophoresis. The genome size of this strain was estimated to be 1,920 kb. By employing Southern hybridization and PCR analysis, 36 genes were located on the map.

Localization of biologically important regions on toxic shock syndrome toxin 1

Toxic shock syndrome toxin 1 (TSST-1) contains a long central alpha helix that forms the base of two grooves on opposite sides of the molecule. Previous studies indicated that residues 132, 135, and 140 along the back of the central alpha helix are important in the biological activities. We made mutations of additional central alpha-helix residues exposed along this groove on the back of TSST-1. The proteins were purified, shown not to have gross alteration in structure, and tested for both superantigenicity and ability to elicit lethal TSS, using the superantigenicity, likely to because of alteration in T-cell receptor binding. Mutants H135A, Q136A, and E132K/ Q136K lost the ability to induce lethal TSS. The mutant Q136A was most increasing because it was superantigenic, yet nonlethal.

Mitogenicity of M5 protein extracted from Streptococcus pyogenes cells is due to streptococcal pyrogenic exotoxin C and mitogenic factor MF

M proteins of Streptococcus pyogenes are virulence factors which impede phagocytosis, bind to many plasma proteins, and induce formation of cross-reactive autoimmune antibodies. Recently, it has been reported that some M proteins, extracted with pepsin from streptococci (pep M), are superantigens. One of these, pep M5, was investigated in detail and was shown to stimulate human T cells bearing V beta 2, V beta 4, and V beta 8. In the present study, we extracted and purified M5 protein by different biochemical methods from two M type 5 group A streptococcal strains. The crude extracts were fractionated by affinity chromatography and ion-exchange chromatography. All fractions were tested in parallel for M protein by immunoblotting and for T-cell-stimulating activity. Although several crude preparations of M5 protein were associated with mitogenicity for V beta 2 and V beta 8 T cells, the M5 proteins, irrespective of the extraction method, could be purified to the extent that they were no longer mitogenic. The mitogenic activity was not destroyed during the purification procedures but was found in fractions separated from M protein. In these fractions, streptococcal pyrogenic exotoxin C and mitogenic factor MF could be detected by protein blotting and enzyme-linked immunosorbent assay. Moreover, anti-M protein sera did not inhibit the mitogenic activity of crude extracts, but antisera which contained anti-streptococcal pyrogenic exotoxin C antibodies showed inhibition. The inability of M5 protein to stimulate T cells was confirmed with recombinant pep M5 produced in Escherichia coli. Our data strongly suggest that the mitogenic activity in M protein preparations is caused by traces of streptococcal superantigens different from M protein.

Superantigens and pseudosuperantigens of gram-positive cocci

Superantigens use an elaborate and unique mechanism of T lymphocyte stimulation. Prototype superantigen are the pyrogenic exotoxins produced by Staphylococcus aureus and Streptococcus pyogenes. Many candidate proteins of bacterial, viral and protozoal origin have recently been reported to be superantigens. In most cases the evidence that these proteins are in fact superantigens is highly indirect. In this review the evidence that gram-positive cocci produce superantigens other than the pyrogenic exotoxins is critically discussed. Evidence in described demonstrating that the epidermolytic toxins of Staphylococcus aureus and the pyrogenic exotoxin B and M-proteins of Streptococcus pyrogenes are not superantigens. Criteria are described for acceptance of a candidate as a superantigen.

Streptococcal toxic-shock syndrome: spectrum of disease, pathogenesis, and new concepts in treatment

Since the 1980s there has been a marked increase in the recognition and reporting of highly invasive group A streptococcal infections with or without necrotizing fasciitis associated with shock and organ failure. Such dramatic cases have been defined as streptococcal toxic-shock syndrome. Strains of group A streptococci isolated from patients with invasive disease have been predominantly M types 1 and 3 that produce pyrogenic exotoxin A or B or both. In this paper, the clinical and demographic features of streptococcal bacteremia, myositis, and necrotizing fasciitis are presented and compared to those of streptococcal toxic-shock syndrome. Current concepts in the pathogenesis of invasive streptococcal infection are also presented, with emphasis on the interaction between group A Streptococcus virulence factors and host defense mechanisms. Finally, new concepts in the treatment of streptococcal toxic-shock syndrome are discussed.

Superantigenic properties of the group A streptococcal exotoxin SpeF (MF)

Streptococcal pyrogenic exotoxin F (SpeF), previously referred to as mitogenic factor, is a newly described potent mitogen produced by group A streptococci. To investigate whether this protein belongs to the family of microbial superantigens, we analyzed the cellular and molecular requirements for its presentation to T cells and compared it with the known streptococcal superantigen pyrogenic exotoxin A (SpeA) and the nonspecific polyclonal T-cell mitogen phytohemagglutinin (PHA). SpeF and SpeA were efficiently presented by autologous antigen-presenting cells (APCs) and an allogeneic B lymphoma cell line, Raji. In contrast, the monocytic cell line U937, which does not express major histocompatibility complex (MHC) class II molecules, failed to present SpeF as well as SpeA but supported the response to PHA. Thus, the presentation of SpeF by APCs was class II dependent but not MHC restricted. The requirement for HLA class II was further supported by the ability of anti-HLA-DQ monoclonal antibody to block the SpeF-induced proliferative response by 75 to 100%. Paraformaldehyde (PFA) fixation of autologous APCs resulted in an impaired ability of SpeF and SpeA to induce optimal T-cell proliferation. In contrast, fixation of Raji cells did not affect the induced proliferation. The stimulatory effect of PHA remained unaffected by both the use of PFA-fixed APCs and the addition of the HLA class II-specific monoclonal antibodies. The addition of a supernatant enriched in interleukin 1 and interleukin 6 to fixed autologous APCs resulted in an increased SpeF-induced response; thus, the impairment was not due to a requirement for processing, but, rather, costimulatory factors produced by metabolically active APCs were needed. SpeF was found to preferentially activate T cells bearing V beta 2, 4, 8, 15, and 19, as determined by quantitative PCR. The data presented clearly show that SpeF is a superantigen. We also studied the prevalence of the speF gene in clinical isolates by Southern blot analyses, and the gene could be detected in 42 group A streptococcal strains, which represented 14 serotypes.

The gene encoding a new mitogenic factor in a Streptococcus pyogenes strain is distributed only in group A streptococci

We recently cloned a gene encoding a new mitogenic factor (MF) from Streptococcus pyogenes NY-5. In the present study, we determined the distribution of this MF gene (mf) by PCR based upon its sequence. Of 371 streptococcal group A strains isolated from clinical specimens, 370 (99.7%) were positive for mf. The strain that was negative for the MF gene was also negative for the streptolysin O gene (slo). Some streptococcal strains belonging to groups C and G were negative for mf but positive for slo. Group B strains were negative for both. Furthermore, we examined the presence of mf in 54 strains belonging to 28 families and found mf only in group A streptococci. These results indicate that mf is distributed specifically in group A streptococci and the presence of mf in clinical samples strongly suggests infection with group A streptococci.

Similar cytokine induction profiles of a novel streptococcal exotoxin, MF, and pyrogenic exotoxins A and B

The cytokine production induced by a newly discovered streptococcal exotoxin, MF, and the pyrogenic exotoxins SpeA and SpeB was determined by in vitro stimulation of peripheral blood mononuclear cells (PBMCs) obtained from healthy blood donors. The induction and kinetics of interleukin-1 alpha (IL-1 alpha), IL-1 beta, IL-1 receptor antagonist, IL-2, IL-3, IL-4, IL-5, IL-6, IL-8, IL-10, gamma interferon, tumor necrosis factor alpha (TNF-alpha), TNF-beta, and granulocyte-macrophage colony-stimulating factor were studied at the single-cell level by use of cytokine-specific monoclonal antibodies and intracellular immunofluorescent juxtanuclear staining. The cytokine-producing cells, with the exception of IL-1-expressing cells, had a characteristic morphology generated by the accumulation of cytokines in the Golgi organelle. MF, SpeA, and SpeB induced a massive gamma interferon and TNF-beta response in 10 to 16% of the PBMCs after 48 to 96 h of cell stimulation. In contrast, IL-2 and TNF-alpha production was detected in only 1 to 3% of the PBMCs. The induction of a lymphocyte TH2 phenotype response, including production of IL-3, IL-4, IL-5, and IL-10, was weak. However, the monokines, IL-1 alpha, IL-1 beta, IL-1 receptor antagonist, and IL-8, were consistently found and gradually produced, peaking at 24 h in approximately 5 to 8% of the PBMCs. MF showed extensive cytokine- and proliferation-inducing capacities equal to those of SpeA and SpeB, which suggests that MF is also a superantigen. A marked interindividual variation could be noted both in the proliferative response and in the cytokine induction of lymphocytes isolated from different individuals, which may be one explanation for the varying clinical severity noticed during group A streptococcal infections.