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

Presence of Group A streptococcus frequently assayed virulence genes in invasive disease: a systematic review and meta-analysis

Introduction

It is currently unclear what the role of Group A streptococcus (GAS) virulence factors (VFs) is in contributing to the invasive potential of GAS. This work investigated the evidence for the association of GAS VFs with invasive disease.

Methods

We employed a broad search strategy for studies reporting the presence of GAS VFs in invasive and non-invasive GAS disease. Data were independently extracted by two reviewers, quality assessed, and meta-analyzed using Stata®.

Results

A total of 32 studies reported on 45 putative virulence factors [invasive (n = 3,236); non-invasive (n = 5,218)], characterized by polymerase chain reaction (PCR) (n = 30) and whole-genome sequencing (WGS) (n = 2). The risk of bias was rated as low and moderate, in 23 and 9 studies, respectively. Meta-,analyses of high-quality studies (n = 23) revealed a significant association of speM [OR, 1.64 (95%CI, 1.06; 2.52)] with invasive infection. Meta-analysis of WGS studies demonstrated a significant association of hasA [OR, 1.91 (95%CI, 1.36; 2.67)] and speG [OR, 2.83 (95%CI, 1.63; 4.92)] with invasive GAS (iGAS). Meta-analysis of PCR studies indicated a significant association of speA [OR, 1.59 (95%CI, 1.10; 2.30)] and speK [OR, 2.95 (95%CI, 1.81; 4.80)] with invasive infection. A significant inverse association was observed between prtf1 [OR, 0.42 (95%CI, 0.20; 0.87)] and invasive infection.

Conclusion

This systematic review and genomic meta-analysis provides evidence of a statistically significant association with invasive infection for the hasA gene, while smeZ, ssa, pnga3, sda1, sic, and NaDase show statistically significantly inverse associations with invasive infection. SpeA, speK, and speG are associated with GAS virulence; however, it is unclear if they are markers of invasive infection. This work could possibly aid in developing preventative strategies.

T-cell receptor Vβ8 for detection of biologically active streptococcal pyrogenic exotoxin type C

Streptococcus pyogenes is an important human pathogen, commonly spread by airborne droplets but also by ingestion of contaminated food. Apart from causing infection, this pathogen produces 13 distinct types of streptococcal pyrogenic exotoxins (SPE). The current method for detection cannot distinguish between the biologically active form of SPE that has been reported to cause foodborne outbreaks and the inactivated toxin that poses no health risk. To measure the biological activity of SPE type C (SPE-C), one such toxin that was linked to foodborne outbreaks associated with milk and milk products, we developed a cell-based assay that can discern between biologically active and inactive SPE-C. To the best of our knowledge, this is the first showing that SPE-C activates T-cells expressing Vβ8. With this finding, we used a T-cell line natively expressing Vβ8 that was genetically engineered to also express the luciferase reporter gene under the regulation of nuclear factor of activated T-cells response element in combination with a B-cell line to present the recombinant SPE-C (rSPE-C) toxin via major histocompatibility complex (MHC) class II to the Vβ8 T-cell receptor (TCR) in an assay to detect and to discern between biologically active and inactive rSPE-C. By using this system, we demonstrated that SPE-C induced significant IL-2 secretion after 72 h and visible light emission after only 5 h, doubling by 24 h. We utilize this finding to assess the specificity of the assay and the effect of pasteurization on SPE-C activity. We observed no cross-reactivity with SPE-B and significant loss of SPE-C biological activity in spiked phosphate-buffered saline while SPE-C spiked into milk is heat stable. Once SPE-C has formed, it is infeasible to eliminate it from milk by thermal treatment.

Pregnancy-Associated Sacroiliitis following an Uncomplicated Pregnancy

Pregnancy-associated sacroiliitis is infrequent during the peripartum period. Although pregnancy-associated pyogenic sacroiliitis rarely occurs, it is associated with significant morbidity and mortality. A timely diagnosis of the disease is challenging due to its nonspecific clinical symptoms. We reviewed a case that experienced an acute illness during pregnancy. The illness was manifested by localized pain in the hips or buttocks, sacroiliac joint tenderness, and debilitating hip pain during ambulation. Magnetic resonance imaging revealed little joint involvement, and the patient was treated with antibiotics, nonsteroidal anti-inflammatory drugs (NSAIDs), and glucocorticoids. The patient responded well to the therapy with marked improvement in her ambulation. Septic sacroiliitis should be considered in peripartum patients presenting with increased inflammatory markers and severe localized pain. Medical management is usually curative and without an adverse effect on pregnancy. Although we could not perform a biopsy to verify the cause of the disease, the patient's excellent response to the treatment confirmed our diagnosis.

Pathogen Stimulation of Interleukin-8 from Human Vaginal Epithelial Cells through CD40

Many bacterial and fungal pathogens cause disease across mucosal surfaces, and to a lesser extent through skin surfaces. Pathogens that potentially cause disease vaginally across epithelial cells include Staphylococcus aureus, group A and B streptococci, Escherichia coli, Neisseria gonorrhoeae, and Candida albicans. We have previously shown that staphylococcal and streptococcal superantigens induce inflammatory chemokines from vaginal epithelial cells through the immune costimulatory molecule CD40 through use of a CRISPR cas9 knockout mutant and complemented epithelial cell line. In this study, we show that the potential vaginal pathogens S. aureus, group A and B streptococci, E. coli, an Enterococcus faecalis strain, and C. albicans in part use CD40 to stimulate interleukin-8 (IL-8) production from human vaginal epithelial cells. In contrast, N. gonorrhoeae does not appear to use CD40 to signal IL-8 production. Normal flora Lactobacillus crispatus and an Enterococcus faecalis strain that produces reutericyclin do not induce IL-8. These data indicate that many potential pathogens, but no normal commensals, induce IL-8 to help disrupt the human vaginal epithelial barrier through CD40, thus providing a potential therapeutic target for drug development. IMPORTANCE Most bacterial and fungal pathogens cause disease across mucosal, and to a lesser extent, skin barriers with the help of induced chemokines from epithelial cells. In this study, we showed that potential vaginal pathogens Staphylococcus aureus, group A and B streptococci, some Enterococcus faecalis strains, Escherichia coli, and Candida albicans use the immune costimulatory molecule CD40 to induce the chemokine interleukin-8 production. In contrast, Neisseria gonorrhoeae does not use CD40 to stimulate interleukin-8. Normal flora lactobacilli and at least one E. faecalis strain do not induce interleukin-8.

A brief review on Group A Streptococcus pathogenesis and vaccine development

Streptococcus pyogenes, also known as Group A Streptococcus (GAS), is a Gram-positive human-exclusive pathogen, responsible for more than 500 000 deaths annually worldwide. Upon infection, GAS commonly triggers mild symptoms such as pharyngitis, pyoderma and fever. However, recurrent infections or prolonged exposure to GAS might lead to life-threatening conditions. Necrotizing fasciitis, streptococcal toxic shock syndrome and post-immune mediated diseases, such as poststreptococcal glomerulonephritis, acute rheumatic fever and rheumatic heart disease, contribute to very high mortality rates in non-industrialized countries. Though an initial reduction in GAS infections was observed in high-income countries, global outbreaks of GAS, causing rheumatic fever and acute poststreptococcal glomerulonephritis, have been reported over the last decade. At the same time, our understanding of GAS pathogenesis and transmission has vastly increased, with detailed insight into the various stages of infection, beginning with adhesion, colonization and evasion of the host immune system. Despite deeper knowledge of the impact of GAS on the human body, the development of a successful vaccine for prophylaxis of GAS remains outstanding. In this review, we discuss the challenges involved in identifying a universal GAS vaccine and describe several potential vaccine candidates that we believe warrant pursuit.

Detection of Streptococcus pyogenes Virulence Factors

Streptococcus pyogenes encodes multiple virulence factors and their presence is often related to the severity of the disease. We designed the system of four low-volume multiplex PCR reactions to detect genes encoding 20 virulence factors: spd3, sdc, sdaB, sdaD, speB, spyCEP, scpA, mac, sic, speL, speK, speM, speC, speI, speA, speH, speG, speJ, smeZ, and ssa. Classification of strains based on the virulence factors absence or presence correlates with PFGE MLST and emm typing results. The typing/detection system is fast and cost-effective, can be used to detect GAS virulence factors and as a rapid tool to effectively differentiate between strains.

Toxins and Superantigens of Group A Streptococci

Streptococcus pyogenes (i.e., the group A Streptococcus) is a human-restricted and versatile bacterial pathogen that produces an impressive arsenal of both surface-expressed and secreted virulence factors. Although surface-expressed virulence factors are clearly vital for colonization, establishing infection, and the development of disease, the secreted virulence factors are likely the major mediators of tissue damage and toxicity seen during active infection. The collective exotoxin arsenal of S. pyogenes is rivaled by few bacterial pathogens and includes extracellular enzymes, membrane active proteins, and a variety of toxins that specifically target both the innate and adaptive arms of the immune system, including the superantigens; however, despite their role in S. pyogenes disease, each of these virulence factors has likely evolved with humans in the context of asymptomatic colonization and transmission. In this article, we focus on the biology of the true secreted exotoxins of the group A Streptococcus, as well as their roles in the pathogenesis of human disease.

A Multiplex Assay for Detection of Staphylococcal and Streptococcal Exotoxins

Staphylococcal and streptococcal exotoxins, also known as superantigens, mediate a range of diseases including toxic shock syndrome, and they exacerbate skin, pulmonary and systemic infections caused by these organisms. When present in food sources they can cause enteric effects commonly known as food poisoning. A rapid, sensitive assay for the toxins would enable testing of clinical samples and improve surveillance of food sources. Here we developed a bead-based, two-color flow cytometry assay using single protein domains of the beta chain of T cell receptors engineered for high-affinity for staphylococcal (SEA, SEB and TSST-1) and streptococcal (SpeA and SpeC) toxins. Site-directed biotinylated forms of these high-affinity agents were used together with commercial, polyclonal, anti-toxin reagents to enable specific and sensitive detection with SD₅₀ values of 400 pg/ml (SEA), 3 pg/ml (SEB), 25 pg/ml (TSST-1), 6 ng/ml (SpeA), and 100 pg/ml (SpeC). These sensitivities were in the range of 4- to 80-fold higher than achieved with standard ELISAs using the same reagents. A multiplex format of the assay showed reduced sensitivity due to higher noise associated with the use of multiple polyclonal agents, but the sensitivities were still well within the range necessary for detection in food sources or for rapid detection of toxins in culture supernatants. For example, the assay specifically detected toxins in supernatants derived from cultures of Staphylococcus aureus. Thus, these reagents can be used for simultaneous detection of the toxins in food sources or culture supernatants of potential pathogenic strains of Staphylococcus aureus and Streptococcus pyogenes.

Analysis of the roles of NrdR and DnaB from Streptococcus pyogenes in response to host defense

Toxic shock syndrome caused by Streptococcus pyogenes (S. pyogenes) is a re-emerging infectious disease. Many virulence-associated proteins play important roles in its pathogenesis and the production of these proteins is controlled by many regulatory factors. CovS is one of the most important two-component sensor proteins in S. pyogenes, and it has been analyzed extensively. Our recent analyses revealed the existence of a transposon between covS and nrdR in several strains, and we speculated that this insertion has some importance. Hence, we examined the significances of the NrdR stand-alone regulator and DnaB, which is encoded by the gene located immediately downstream of nrdR in S. pyogenes infection. We established an nrdR-only knockout strain, and both nrdR and partial dnaB knockout strain. These established knockout strains exhibited a deteriorated response to H2 O2 exposure. nrdR and partial dnaB knockout strain was more easily killed by human polynuclear blood cells, but the nrdR-only knockout strain had no significant difference compared to wild type in contrast to the combined knockout strain. In addition, the mouse infection model experiment illustrated that nrdR and partial dnaB knockout strain, but not the nrdR-only knockout strain, was less virulent compared with the parental strain. These results suggest that DnaB is involved in response to host defense.

Antimicrobial Peptide Resistance Mechanisms of Gram-Positive Bacteria

Antimicrobial peptides, or AMPs, play a significant role in many environments as a tool to remove competing organisms. In response, many bacteria have evolved mechanisms to resist these peptides and prevent AMP-mediated killing. The development of AMP resistance mechanisms is driven by direct competition between bacterial species, as well as host and pathogen interactions. Akin to the number of different AMPs found in nature, resistance mechanisms that have evolved are just as varied and may confer broad-range resistance or specific resistance to AMPs. Specific mechanisms of AMP resistance prevent AMP-mediated killing against a single type of AMP, while broad resistance mechanisms often lead to a global change in the bacterial cell surface and protect the bacterium from a large group of AMPs that have similar characteristics. AMP resistance mechanisms can be found in many species of bacteria and can provide a competitive edge against other bacterial species or a host immune response. Gram-positive bacteria are one of the largest AMP producing groups, but characterization of Gram-positive AMP resistance mechanisms lags behind that of Gram-negative species. In this review we present a summary of the AMP resistance mechanisms that have been identified and characterized in Gram-positive bacteria. Understanding the mechanisms of AMP resistance in Gram-positive species can provide guidelines in developing and applying AMPs as therapeutics, and offer insight into the role of resistance in bacterial pathogenesis.

Staphylococcal and streptococcal superantigen exotoxins

SUMMARY This review begins with a discussion of the large family of Staphylococcus aureus and beta-hemolytic streptococcal pyrogenic toxin T lymphocyte superantigens from structural and immunobiological perspectives. With this as background, the review then discusses the major known and possible human disease associations with superantigens, including associations with toxic shock syndromes, atopic dermatitis, pneumonia, infective endocarditis, and autoimmune sequelae to streptococcal illnesses. Finally, the review addresses current and possible novel strategies to prevent superantigen production and passive and active immunization strategies.

A natural inactivating mutation in the CovS component of the CovRS regulatory operon in a pattern D Streptococcal pyogenes strain influences virulence-associated genes

A skin-tropic invasive group A Streptococcus pyogenes (GAS) strain, AP53, contains a natural inactivating mutation in the covS gene (covS(M)) of the two-component responder (CovR)/sensor (CovS) gene regulatory system. The effects of this mutation on specific GAS virulence determinants have been assessed, with emphasis on expression of the extracellular protease, streptococcal pyrogenic exotoxin B (SpeB), capsular hyaluronic acid, and proteins that allow host plasmin assembly on the bacterial surface, viz. a high affinity plasminogen (Pg)/plasmin receptor, Pg-binding group A streptococcal M protein (PAM), and the human Pg activator streptokinase. To further illuminate mechanisms of the functioning of CovRS in the virulence of AP53, two AP53 isogenic strains were generated, one in which the natural covS(M) gene was mutated to WT-covS (AP53/covS(WT)) and a strain that contained an inactivated covR gene (AP53/ΔcovR). Two additional strains that do not contain PAM, viz. WT-NS931 and NS931/covS(M), were also employed. SpeB was not measurably expressed in strains containing covR(WT)/covS(M), whereas in strains with natural or engineered covR(WT)/covS(WT), SpeB expression was highly up-regulated. Alternatively, capsule synthesis via the hasABC operon was enhanced in strain AP53/covS(M), whereas streptokinase expression was only slightly affected by the covS inactivation. PAM expression was not substantially influenced by the covS mutation, suggesting that covRS had minimal effects on the mga regulon that controls PAM expression. These results demonstrate that a covS inactivation results in virulence gene alterations and also suggest that the CovR phosphorylation needed for gene up- or down-regulation can occur by alternative pathways to CovS kinase.

Gram-positive bacterial superantigen outside-in signaling causes toxic shock syndrome

Staphylococcus aureus and Streptococcus pyogenes (group A streptococci) are Gram-positive pathogens capable of producing a variety of bacterial exotoxins known as superantigens. Superantigens interact with antigen-presenting cells (APCs) and T cells to induce T cell proliferation and massive cytokine production, which leads to fever, rash, capillary leak and subsequent hypotension, the major symptoms of toxic shock syndrome. Both S. aureus and group A streptococci colonize mucosal surfaces, including the anterior nares and vagina for S. aureus, and the oropharynx and less commonly the vagina for group A streptococci. However, due to their abilities to secrete a variety of virulence factors, the organisms can also cause illnesses from the mucosa. This review provides an updated discussion of the biochemical and structural features of one group of secreted virulence factors, the staphylococcal and group A streptococcal superantigens, and their abilities to cause toxic shock syndrome from a mucosal surface. The main focus of this review, however, is the abilities of superantigens to induce cytokines and chemokines from epithelial cells, which has been linked to a dodecapeptide region that is relatively conserved among all superantigens and is distinct from the binding sites required for interactions with APCs and T cells. This phenomenon, termed outside-in signaling, acts to recruit adaptive immune cells to the submucosa, where the superantigens can then interact with those cells to initiate the final cytokine cascades that lead to toxic shock syndrome.

Analysis of the pathological lesions of the lung in a mouse model of cutaneous infection with Streptococcus pyogenes

Invasive diseases such as toxic shock syndrome caused by Streptococcus pyogenes (S. pyogenes) are re-emerging infectious diseases. The mechanism of pathogenesis is not completely understood although the virulence of this organism has been analyzed using animal model systems, particularly using mice. The analysis of the progression of infection, however, is difficult. Computed tomography (CT) scanning is an extremely powerful technique that we applied to the mouse model of cutaneous infection with S. pyogenes. Two or three days after subcutaneous administration of bacteria, high density reticular areas were detected in the lung by CT. Histopathological examination of the lung was performed to examine the results of CT. Increased numbers of cytokeratin-positive epithelial cells, probably alveolar type II epithelial cells, were detected but no remarkable increase of inflammatory cell infiltrates was observed. Our results show that the pathological lesions of the lung in this model, wherein relatively few numbers of neutrophils were in the alveoli, are well correlated with the lung of a part of streptococcal toxic shock syndrome patients. Therefore, CT may be useful in assessing the progression of S. pyogenes infection, particularly in the pathological lesions of the lung in this model.

Postpartum group a Streptococcus sepsis and maternal immunology

Group A Streptococcus (GAS) is an historically important agent of puerperal infections and sepsis. The inception of hand-washing and improved hospital hygiene drastically reduced the incidence of puerperal sepsis, but recently the incidence and severity of postpartum GAS infections has been rising for uncertain reasons. Several epidemiological, host, and microbial factors contribute to the risk for GAS infection and mortality in postpartum women. These include the mode of delivery (vaginal versus cesarean section), the location where labor and delivery occurred, exposure to GAS carriers, the altered immune status associated with pregnancy, the genetic background of the host, the virulence of the infecting GAS strain, and highly specialized immune responses associated with female reproductive tract tissues and organs. This review will discuss the complicated factors that contribute to the increased susceptibility to GAS after delivery and potential reasons for the recent increase observed in morbidity and mortality.

Analysis of two-component sensor proteins involved in the response to acid stimuli in Streptococcus pyogenes

The virulence of Streptococcus pyogenes depends on proteins that are produced by this bacterium. The production of virulence proteins depends on environmental factors, and two-component regulatory systems are considered to be involved in sensing these factors. One of the environmental factors is acid stimuli. We established knockout strains in all speculated two-component regulatory sensor proteins of the M1 clinical strain of S. pyogenes and examined their relevance to acid stimuli. The parental strain and its derived knockout strains were cultured in a medium adjusted to pH 7.6 or 6.0, and their growth in broth was compared. The spy1622 sensor knockout strain showed significant growth reduction compared with the parental strain in broth at pH 6.0, suggesting that the Spy1622 two-component sensor protein is involved in sensing acid stimuli. To further examine the role of the Spy1622 two-component sensor protein in virulence, blood bactericidal assays and mouse infection model experiments were performed. We found that the spy1622 knockout strain was less virulent than the parental strain, which suggests that the Spy1622 two-component sensor protein could play an important role in virulence.

Invasive group A, C and G streptococcal disease in western Norway: virulence gene profiles, clinical features and outcomes

Invasive group A streptococcal (iGAS) disease is endemic in Norway, but data on invasive group C and group G streptococcal (iGCS/GGS) disease are lacking. We investigated the characteristics of iGAS and iGCS/GGS infections in western Norway from March 2006 to February 2009. Clinical information was retrospectively obtained from medical records. GAS and GCS/GGS isolates were emm typed and screened for the presence of 11 superantigen (SAg) genes and the gene encoding streptococcal phospholipase A₂ (SlaA). GCS/GGS isolates were also subjected to PCR with primers targeting speG(dys) . Sixty iGAS and 50 iGCS/GGS cases were identified, corresponding to mean annual incidence rates of 5.0 per 100,000 and 4.1 per 100,000 inhabitants, respectively. Skin and soft tissue infections were the most frequent clinical manifestations of both iGAS and iGCS/GGS disease, and 14 iGAS patients (23%) developed necrotizing fasciitis. The 30-day case fatality rates of iGAS and iGCS/GGS disease were 10% and 2%, respectively. emm1, emm3 and emm28 accounted for 53% of the GAS isolates, and these types were associated with severe clinical outcome. SAg gene and SlaA profiles were conserved within most of the GAS emm types, although five profiles were obtained within isolates of emm28. stG643 was the most prevalent GCS/GGS emm type, and speG(dys) was identified in 73% of the GCS/GGS isolates. Neither GAS SAg genes nor SlaA were detected in GCS/GGS. Our findings indicate a considerable burden of both iGAS and iGCS/GGS disease and a high frequency of necrotizing fasciitis caused by GAS in our community.

Epidemiological markers of Streptococcus pyogenes strains in Tunisia

To further understand the epidemiology of Streptococcus pyogenes or group A streptococcus (GAS) infections in Tunisia, phenotypic and genomic markers of GAS isolates, including antibiotic susceptibility, biotypes, T and emm types and toxin gene profiles, have been characterized. A total of 103 isolates, collected between 2000 and 2006, were investigated; 47 were recovered from invasive infections, and 56 from non-invasive infections. Rates of resistance to tetracycline, erythromycin, clindamycin and rifampin were 70.8%, 4.8%, 4.8% and 0.9%, respectively. High levels of resistance to streptomycin and kanamycin were observed in 1.9% and 4.8% of isolates, respectively. Biotype 3 was most common. Twenty different T patterns were observed, with a predominance of T3/13/B3264, and 38 different emm types. In both invasive and non-invasive isolates, emm118 (9.7%), emm42 (8.7%), emm1 (7.8%), st432 (6.8%), emm28 (5.8%) and emm76 (5.8%) were the most prevalent types; emm1, emm76 and emm18 were mainly observed among invasive infections, whereas emm118 (12.5%), emm42 (10.7%) and emm28 (8.9%) were predominant among non-invasive infections. The speB gene was detected in all isolates, but there were variable frequencies of speA, speC and ssa (20.3%, 32% and 25.2% respectively). Significant associations of emm1, emm18 and emm3 with speA and of emm4 and st432 with ssa were found. This first report from Tunisia revealed a unique emm distribution of GAS that differs from those of other regions. This information on the distribution of such emm types will be useful for the development of an appropriate vaccine in a country where the incidence of rheumatic fever remains high.

Variation in Streptococcus pyogenes NAD+ glycohydrolase is associated with tissue tropism

Streptococcus pyogenes is an important pathogen that causes a variety of diseases. The most common infections involve the throat (pharyngitis) or skin (impetigo); however, the factors that determine tissue tropism and severity are incompletely understood. The S. pyogenes NAD(+) glycohydrolase (SPN) is a virulence factor that has been implicated in contributing to the pathogenesis of severe infections. However, the role of SPN in determining the bacterium's tissue tropism has not been evaluated. In this report, we examine the sequences of spn and its endogenous inhibitor ifs from a worldwide collection of S. pyogenes strains. Analysis of average pairwise nucleotide diversity, average number of nucleotide differences, and ratio of nonsynonymous to synonymous substitutions revealed significant diversity in spn and ifs. Application of established models of molecular evolution shows that SPN is evolving under positive selection and diverging into NAD(+) glycohydrolase (NADase)-active and -inactive subtypes. Additionally, the NADase-inactive SPN subtypes maintain the characteristics of a functional gene while ifs becomes a pseudogene. Thus, NADase-inactive SPN continues to evolve under functional constraint. Furthermore, NADase activity did not correlate with invasive disease in our collection but was associated with tissue tropism. The ability to cause infection at both the pharynx and the skin ("generalist" strains) is correlated with NADase-active SPN, while the preference for causing infection at either the throat or the skin ("specialist" strains) is associated with NADase-inactive SPN. These findings suggest that SPN has a NADase-independent function and prompt a reevaluation of the role of SPN in streptococcal pathogenesis.

Characterization of a virulence-associated and cell-wall-located DNase of Streptococcus pyogenes

We investigated culture supernatant proteins from the M1 serotype of Streptococcus pyogenes by two-dimensional gel electrophoresis and peptide mass mapping analysis, and characterized the single protein spots. Among them, we analysed the Spy0747 protein. This protein is homologous to the SsnA protein, a cell-wall-located DNase expressed in Streptococcus suis serotype 2. We designated the Spy0747 protein as SpnA. SpnA protein was also detected in the insoluble fraction of whole-cell lysates using shotgun proteomic analysis, suggesting that SpnA is also located in the cell wall. SpnA was expressed as a glutathione S-transferase-fusion protein in Escherichia coli. We confirmed that the recombinant protein had DNase activity that was dependent on Ca(2+) and Mg(2+), like SsnA. Blood bactericidal assays and mouse infection model experiments showed that the spnA knockout strain was less virulent than the parental strain, thus suggesting that SpnA could play an important role in virulence. Using PCR, we found that the spnA gene was present in all clinical S. pyogenes strains we examined. Our results, together with a previous report identifying Spy0747 as a surface-associated protein, suggest that SpnA is an important cell-wall-located DNase that is generally produced in S. pyogenes and is involved in virulence.

Immune cell subsets in necrotizing fasciitis: an immunohistochemical analysis

Current concepts of the pathophysiology of necrotizing fasciitis (NF), a life-threatening infection of soft tissues associated with a toxic shock syndrome, emphasizes the role of bacterial superantigens as mediators of cytokine release by immune lymphocytes. In order to assess the cellular basis of immune activation, immunohistochemistry was applied to the analysis of inflammatory cell subsets in situ in 13 patients with NF. The percentage of inflammatory cells in skin and soft tissue was scored from 0 to 3+ (>50%). Substantial numbers of CD15+ polymorphonuclear leukocytes were present in 12 of 13 patients. CD3+ T-lymphocytes accounted for >10%, CD68+ macrophages for >50%, and Factor XIIIa+ mononuclear cells for >10% of the mononuclear cell infiltrates, respectively, in 10 of 13 patients, whereas CD1a+ cells were present in only 3 of 13 cases and accounted for <10% of mononuclear inflammatory cells. We conclude that immune lymphocytes and accessory immune cells are represented in substantial numbers in the early lesions of NF, and their presence supports current concepts with respect to the pathophysiology of this disorder.

Cytolysins augment superantigen penetration of stratified mucosa

Staphylococcus aureus and Streptococcus pyogenes colonize mucosal surfaces of the human body to cause disease. A group of virulence factors known as superantigens are produced by both of these organisms that allows them to cause serious diseases from the vaginal (staphylococci) or oral mucosa (streptococci) of the body. Superantigens interact with T cells and APCs to cause massive cytokine release to mediate the symptoms collectively known as toxic shock syndrome. In this study we demonstrate that another group of virulence factors, cytolysins, aid in the penetration of superantigens across vaginal mucosa as a representative nonkeratinized stratified squamous epithelial surface. The staphylococcal cytolysin alpha-toxin and the streptococcal cytolysin streptolysin O enhanced penetration of toxic shock syndrome toxin-1 and streptococcal pyrogenic exotoxin A, respectively, across porcine vaginal mucosa in an ex vivo model of superantigen penetration. Upon histological examination, both cytolysins caused damage to the uppermost layers of the vaginal tissue. In vitro evidence using immortalized human vaginal epithelial cells demonstrated that although both superantigens were proinflammatory, only the staphylococcal cytolysin alpha-toxin induced a strong immune response from the cells. Streptolysin O damaged and killed the cells quickly, allowing only a small release of IL-1beta. Two separate models of superantigen penetration are proposed: staphylococcal alpha-toxin induces a strong proinflammatory response from epithelial cells to disrupt the mucosa enough to allow for enhanced penetration of toxic shock syndrome toxin-1, whereas streptolysin O directly damages the mucosa to allow for penetration of streptococcal pyrogenic exotoxin A and possibly viable streptococci.

Novel toxic shock syndrome toxin-1 amino acids required for biological activity

Superantigens interact with T lymphocytes and macrophages to cause T lymphocyte proliferation and overwhelming cytokine production, which lead to toxic shock syndrome. Staphylococcus aureus superantigen toxic shock syndrome toxin-1 is a major cause of menstrual toxic shock syndrome. In general, superantigen-secreting S. aureus remains localized at the vaginal surface, and the superantigen must therefore penetrate the vaginal mucosa to interact with underlying immune cells to cause toxic shock syndrome. A dodecapeptide region (toxic shock syndrome toxin-1 amino acids F119-D130), relatively conserved among superantigens, has been implicated in superantigen penetration of the epithelium. The purpose of this study was to determine amino acids within this dodecapeptide region that are required for interaction with vaginal epithelium. Alanine mutations were constructed in S. aureus toxic shock syndrome toxin-1 amino acids D120 to D130. All mutants maintained superantigenicity, and selected mutants were lethal when given intravenously to rabbits. Toxic shock syndrome toxin-1 induces interleukin-8 from immortalized human vaginal epithelial cells; however, three toxin mutants (S127A, T128A, and D130A) induced low levels of interleukin-8 compared to wild type toxin. When carboxy-terminal mutants (S127A to D130A) were administered vaginally to rabbits, D130A was nonlethal, while S127A and T128A demonstrated delayed lethality compared to wild type toxin. In a porcine ex vivo permeability model, mutant D130A penetrated the vaginal mucosa more quickly than wild type toxin. Toxic shock syndrome toxin-1 residue D130 may contribute to binding an epithelial receptor, which allows it to penetrate the vaginal mucosa, induce interleukin-8, and cause toxic shock syndrome.

Rapidly fatal infections

Emergency physicians are trained to separate “sick” from “not sick” patients during their training. Nevertheless, every emergency physician will face situations in which early intervention is critical to their patient's outcome. Infectious diseases are responsible for many of these potentially poor outcomes. This article discusses early identification and treatment for several rapidly fatal infections, including two newly identified travel-related illnesses.

Superantigens SPEA and SMEZ do not affect secretome expression in Streptococcus pyogenes

The superantigens, toxic shock syndrome toxin-1 (TSST-1) and staphylococcal enterotoxin B (SEB), were recently reported to repress global exoprotein synthesis in Staphylococcus aureus. To investigate if this phenomenon could be observed in a different Gram-positive pathogen, the effects of two major Streptococcus pyogenes superantigens on streptococcal secretome expression were examined. Using mutagenesis and genetic complementation, we demonstrated that neither streptococcal pyrogenic exotoxin A (SPEA) nor streptococcal mitogenic exotoxin Z (SMEZ) had any consistent effect on global protein expression or on transcription of genes encoding the secreted exoproteins, DNase B, SPEB and SPEG. In S. pyogenes, superantigen production does not appear to have a major regulatory role.

Genetic variation in group A streptococci

Group A streptococcus (GAS) is responsible for a range of human diseases that vary in their clinical manifestations and severity. While numerous virulence factors have been described, the way these factors interact to promote different streptococcal diseases is less clear. In order to identify multifactorial relationships between GAS and the human host, novel high-throughput techniques such as microarrays are necessary. We have performed comparative studies using custom-designed virulence arrays to enhance our understanding of the high degree of genotypic variation that occurs in streptococci. This study has pointed to mobile genetic elements as the major agents that promote variation. Our results show that multiple combinations of genes might bring about similar clinical pictures. This adds further complexity to the intricate relationship between pathogen and host.

Virulence profiling of Streptococcus dysgalactiae subspecies equisimilis isolated from infected humans reveals 2 distinct genetic lineages that do not segregate with their phenotypes or propensity to cause diseases

BACKGROUND

In spite of the emerging importance of Streptococcus dysgalactiae subspecies equisimilis (human group C streptococci [GCS] and group G streptococci [GGS]) in human health, its molecular makeup remains largely undefined. Apart from sharing a phylogenetic relationship with the human pathogen group A streptococci (GAS), GCS/GGS and GAS colonize the same ecological niche and exhibit considerable overlap in their disease profiles. Such similarities imply that the virulence factors associated with diseases may also be similar.

METHODS

In this study, we used a targeted microarray containing 216 GAS virulence genes to profile the virulence gene repertoires of 58 S. dysgalactiae subspecies equisimilis isolates recovered during human infections. We performed comparative analyses to investigate the relationship between GAS virulence genes in and the invasive potential of GCS/GGS.

RESULTS

Up to one-half of the GAS virulence genes represented in the microarray were identified in GCS/GGS. No statistical differences were observed between isolates harboring the group C versus group G carbohydrates; however, clustering algorithms revealed 2 genetically distinct clusters of S. dysgalactiae subspecies equisimilis isolates. No relationship was observed between the virulence profile of GCS/GGS and the propensity for disease or the tissue site of isolation.

CONCLUSIONS

This is, to our knowledge, the first comprehensive analysis of the virulence profile of S. dysgalactiae subspecies equisimilis, and it enables novel insights into the pathogen's genetic basis of disease propensity shared with GAS. Human group C and group G streptococci may not be considered to be separate species; in fact, they may constitute 2 distinct lineages. Additional incongruent relationships were observed between virulence profiles and GCS/GGS disease propensity.

Identification and characterization of bicistronic speB and prsA gene expression in the group A Streptococcus

Severe, invasive group A streptococcal infections have reemerged worldwide, and extracellular toxins, including streptococcal pyrogenic exotoxin B (SpeB), have been implicated in pathogenesis. The genetic regulation of SpeB is not fully understood, and the mechanisms involved in the processing of the protoxin to its enzymatically active form have not been definitively established. The present work demonstrated that the genes encoding SpeB (speB) and a peptidyl-prolyl isomerase (prsA) constitute an operon with transcription initiated from two promoters upstream of speB. Further, the speB-prsA operon was transcribed as a bicistronic mRNA. This finding is in contrast to the generally accepted notion that speB is transcribed only as a monocistronic gene. In addition, prsA has its own promoter, and transcription from this promoter starts in early log phase, prior to the transcription of speB. Genomic disruption of prsA decreased the production of enzymatically active SpeB but not the level of the pro-SpeB zymogen. Taken together, these results demonstrate that prsA is required for production of fully mature, enzymatically active SpeB.

Genes for the majority of group a streptococcal virulence factors and extracellular surface proteins do not confer an increased propensity to cause invasive disease

BACKGROUND

The factors behind the reemergence of severe, invasive group A streptococcal (GAS) diseases are unclear, but it could be caused by altered genetic endowment in these organisms. However, data from previous studies assessing the association between single genetic factors and invasive disease are often conflicting, suggesting that other, as-yet unidentified factors are necessary for the development of this class of disease.

METHODS

In this study, we used a targeted GAS virulence microarray containing 226 GAS genes to determine the virulence gene repertoires of 68 GAS isolates (42 associated with invasive disease and 28 associated with noninvasive disease) collected in a defined geographic location during a contiguous time period. We then employed 3 advanced machine learning methods (genetic algorithm neural network, support vector machines, and classification trees) to identify genes with an increased association with invasive disease.

RESULTS

Virulence gene profiles of individual GAS isolates varied extensively among these geographically and temporally related strains. Using genetic algorithm neural network analysis, we identified 3 genes with a marginal overrepresentation in invasive disease isolates. Significantly, 2 of these genes, ssa and mf4, encoded superantigens but were only present in a restricted set of GAS M-types. The third gene, spa, was found in variable distributions in all M-types in the study.

CONCLUSIONS

Our comprehensive analysis of GAS virulence profiles provides strong evidence for the incongruent relationships among any of the 226 genes represented on the array and the overall propensity of GAS to cause invasive disease, underscoring the pathogenic complexity of these diseases, as well as the importance of multiple bacteria and/or host factors.

Genetic diversity and exotoxin A production of group A streptococci causing sepsis

The M protein and streptococcus pyrogenic exotoxin (SPE A) are important virulence factors in group A streptococci (GAS) infections. The emm types of GAS strains isolated from patients with sepsis were determined by sequencing the 5' N-terminus of the emm gene, encoding the M protein, and clonality analysis using pulsed-field gel electrophoresis. The presence of speA and production of SPE A were also examined. There were no predominant GAS clones. The emm genotypes were variable, and the most common genotype was emm13 (17.9%). The production prevalence of SPE A was 21.4%. The low mortality rate (7.1%) of GAS sepsis might be attributable to the low incidence of virulent strains such as emm1 (10.7%) and emm3 (7.1%), as well as to low production rate of SPE A.

Association of group A streptococcal emm types with virulence traits and macrolide-resistance genes is independent of the source of isolation

Streptococcus pyogenes (group A streptococci; GAS) recovered from paediatric pharyngitis (101 isolates) and asymptomatic children (79 isolates) in the same geographical area and period, as well as isolates collected during an enhanced national surveillance programme for GAS invasive diseases (79 isolates), were screened for the incidence of the streptococcal pyrogenic exotoxin (spe) genes speA and speC, as well as the macrolide-resistance genes erm(B), erm(A) subclass erm(TR) and mef(A), and typed by emm sequencing. The speA gene was detected with comparable incidence among throat isolates (13.9 % of asymptomatic children and 16.8 % of pharyngitis isolates) and in 25 % of invasive cases; in contrast, speC incidence was, surprisingly, higher in paediatric populations (55.4 % in pharyngitis isolates and 65.8 % in asymptomatic children) than in invasive isolates (30 %; P < 0.0001). Macrolide resistance was detected in 26.6, 38.0 and 37.6 % of strains belonging to invasive, asymptomatic and pharyngitis populations, respectively. The different incidences of exotoxin and antibiotic-resistance genes among populations did not appear to have an intrinsic clinical significance, but may reflect the propensity of these traits to be associated with certain emm types independent of the source from which the strains were isolated. Further investigations with larger emm-type populations are warranted to confirm this.

Variations in emm type among group A streptococcal isolates causing invasive or noninvasive infections in a nationwide study

Since the late 1980s several studies have described the increased incidence and severity of invasive group A streptococcal (GAS) infections. However, most studies on GAS pathogenesis have focused on information obtained during outbreaks. We analyzed isolate distribution and host susceptibility as part of a nationwide prospective surveillance study performed between January 2001 and August 2002. GAS isolates collected from 201 patients with invasive infections, 335 patients with noninvasive infections, and 17 asymptomatic carriers were characterized with respect to their emm types and superantigen genotypes. The superantigen-neutralizing capacity and levels of antibodies against streptolysin O and DNAse B were determined for isolates from the sera from 36 invasive cases and 91 noninvasive cases. emm type 1 (emm-1) isolates were significantly more common among invasive cases, whereas emm-4, emm-6, and emm-12 dominated among the noninvasive cases. The distributions of the phage-associated superantigen genes (speA, speC, speH, speI, ssa) differed among invasive and noninvasive isolates, mainly due to their linkage to certain emm types. No significant differences in serum superantigen-neutralizing capacities were observed. The levels of anti-streptolysin O and anti-DNAse B antibodies were highest in the sera from invasive cases. Our study emphasizes the importance of obtaining data during years with stable incidences, which will enable evaluation of future outbreak data.

Reemergence of emm1 and a changed superantigen profile for group A streptococci causing invasive infections: results from a nationwide study

Between 1999 and 2002, 496 invasive group A streptococcal (GAS) isolates from clinical microbiological departments in Denmark and subsequently 487 (98%) questionnaires from the clinicians treating the patients were received as part of a national surveillance. emm types and streptococcal superantigen (SAg) genes were determined. The incidence of invasive GAS infections was on average 2.3 per 100,000 per year. Bacteremia with no focal symptoms (27%) was together with erysipelas (20%) the most prevalent clinical diagnoses. Streptococcal toxic shock syndrome occurred in 10% of patients, of which 56% died. The overall case fatality rate within 30 days was 23%. In total, 47 different emm types were identified, of which emm1, emm3, emm4, emm12, emm28, and emm89 were identified in 72% of the 493 available isolates. During the 4-year period the presence of emm1 increased from 16% in 1999 to 40% in 2002. Concurrently, the presence of emm3 decreased from 23% in 1999 to 2% in 2002. The emm1 isolates predominantly carried speA, although the frequency decreased from 94% in 1999 to 71% in 2002, whereas the emm1-specific prevalence of speC increased from 25 to 53%. In a historical perspective, this could be interpreted as a reemergence of emm1 and could indicate a possible introduction of a new emm1 subclone. However, this reemergence did not result in any significant changes in the clinical manifestations during the study period. Our results show the complexity of invasive GAS infections, with time-dependent variations in the incidence and distribution of emm and SAg genes, which emphasizes the need for continuous epidemiological and molecular investigations.

Crystal structure of a dimeric form of streptococcal pyrogenic exotoxin A (SpeA1)

Streptococcal pyrogenic exotoxin A (SpeA1) is a bacterial superantigen associated with scarlet fever and streptococcal toxic shock syndrome (STSS). SpeA1 is found in both monomeric and dimeric forms, and previous work suggested that the dimer results from an intermolecular disulfide bond between the cysteines at positions 90 of each monomer. Here, we present the crystal structure of the dimeric form of SpeA1. The toxin crystallizes in the orthorhombic space group P212121, with two dimers in the crystallographic asymmetric unit. The final structure has a crystallographic R-factor of 21.52% for 7248 protein atoms, 136 water molecules, and 4 zinc atoms (one zinc atom per molecule). The implications of SpeA1 dimer on MHC class II and T-cell receptor recognition are discussed.

Epidemiological features of invasive and noninvasive group A streptococcal disease in the Netherlands, 1992-1996

A prospective, nationwide, laboratory-based surveillance of invasive group A streptococcal infections was conducted in the Netherlands from 1992 through 1996. Clinical and demographic data were obtained and all isolates were T/M typed. All noninvasive group A streptococcal isolates were registered from 1994 through 1996. A total of 880 patients with invasive streptococcal disease were identified. The annual incidence was found to be 2.2 per 100,000. Predominant M types were M1 (21%), M3 (11%), M6 (5%), M12 (5%), and M28 (8%). Particular age and M-type distributions were observed in different clinical entities. The case-fatality rate was 18% overall, but it reached 59% among cases of toxic shock-like syndrome. Older age, necrotizing fasciitis, sepsis without focus, pneumonia, infection with type M1 or M3 strains, and underlying cardiopulmonary disease were associated with fatality. A total of 10,105 patients with noninvasive group A streptococcal disease were registered. These patients differed significantly from patients with invasive disease with regard to age distribution and primary foci of infection.

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.

Biology and pathogenesis of thrombosis and procoagulant activity in invasive infections caused by group A streptococci and Clostridium perfringens

Group A streptococcal necrotizing fasciitis/myonecrosis and Clostridium perfringens gas gangrene are two of the most fulminant gram-positive infections in humans. Tissue destruction associated with these infections progresses rapidly to involve an entire extremity. Multiple-organ failure is common, and morbidity and mortality remain high. Systemic activation of coagulation and dysregulation of the anticoagulation pathways contribute to the pathogenesis of many diverse disease entities of infectious etiology, and it has been our hypothesis that microvascular thrombosis contributes to reduced tissue perfusion, hypoxia, and subsequent regional tissue necrosis and organ failure in these invasive gram-positive infections. This article reviews the coagulation, anticoagulation, and fibrinolytic systems from cellular players to cytokines to novel antithrombotic therapies and discusses the mechanisms contributing to occlusive microvascular thrombosis and tissue destruction in invasive group A streptococcal and C. perfringens infections. A thorough understanding of these mechanisms may suggest novel therapeutic targets for patients with these devastating infections.