Association of phenotypic and genotypic characteristics of invasive Streptococcus pyogenes isolates with clinical components of streptococcal toxic shock syndrome

Immunomodulating Enzymes from Streptococcus pyogenes-In Pathogenesis, as Biotechnological Tools, and as Biological Drugs

Streptococcus pyogenes, or Group A Streptococcus, is an exclusively human pathogen that causes a wide variety of diseases ranging from mild throat and skin infections to severe invasive disease. The pathogenesis of S. pyogenes infection has been extensively studied, but the pathophysiology, especially of the more severe infections, is still somewhat elusive. One key feature of S. pyogenes is the expression of secreted, surface-associated, and intracellular enzymes that directly or indirectly affect both the innate and adaptive host immune systems. Undoubtedly, S. pyogenes is one of the major bacterial sources for immunomodulating enzymes. Major targets for these enzymes are immunoglobulins that are destroyed or modified through proteolysis or glycan hydrolysis. Furthermore, several enzymes degrade components of the complement system and a group of DNAses degrade host DNA in neutrophil extracellular traps. Additional types of enzymes interfere with cellular inflammatory and innate immunity responses. In this review, we attempt to give a broad overview of the functions of these enzymes and their roles in pathogenesis. For those enzymes where experimentally determined structures exist, the structural aspects of the enzymatic activity are further discussed. Lastly, we also discuss the emerging use of some of the enzymes as biotechnological tools as well as biological drugs and vaccines.

Human IgG Increases Virulence of Streptococcus pyogenes through Complement Evasion

Streptococcus pyogenes is an exclusively human pathogen that can provoke mild skin and throat infections but can also cause fatal septicemia. This gram-positive bacterium has developed several strategies to evade the human immune system, enabling S. pyogenes to survive in the host. These strategies include recruiting several human plasma proteins, such as the complement inhibitor, C4b-binding protein (C4BP), and human (hu)-IgG through its Fc region to the bacterial surface to evade immune recognition. We identified a novel virulence mechanism whereby IgG-enhanced binding of C4BP to five of 12 tested S. pyogenes strains expressed diverse M proteins that are important surface-expressed virulence factors. Importantly, all strains that bound C4BP in the absence of IgG bound more C4BP when IgG was present. Further studies with an M1 strain that additionally expressed protein H, also a member of the M protein family, revealed that binding of hu-IgG Fc to protein H increased the affinity of protein H for C4BP. Increased C4BP binding accentuated complement downregulation, resulting in diminished bacterial killing. Accordingly, mortality from S. pyogenes infection in hu-C4BP transgenic mice was increased when hu-IgG or its Fc portion alone was administered concomitantly. Electron microscopy analysis of human tissue samples with necrotizing fasciitis confirmed increased C4BP binding to S. pyogenes when IgG was present. Our findings provide evidence of a paradoxical function of hu-IgG bound through Fc to diverse S. pyogenes isolates that increases their virulence and may counteract the beneficial effects of IgG opsonization.

The majority of 9,729 group A streptococcus strains causing disease secrete SpeB cysteine protease: pathogenesis implications

Group A streptococcus (GAS), the causative agent of pharyngitis and necrotizing fasciitis, secretes the potent cysteine protease SpeB. Several lines of evidence suggest that SpeB is an important virulence factor. SpeB is expressed in human infections, protects mice from lethal challenge when used as a vaccine, and contributes significantly to tissue destruction and dissemination in animal models. However, recent descriptions of mutations in genes implicated in SpeB production have led to the idea that GAS may be under selective pressure to decrease secreted SpeB protease activity during infection. Thus, two divergent hypotheses have been proposed. One postulates that SpeB is a key contributor to pathogenesis; the other, that GAS is under selection to decrease SpeB during infection. In order to distinguish between these alternative hypotheses, we performed casein hydrolysis assays to measure the SpeB protease activity secreted by 6,775 GAS strains recovered from infected humans. The results demonstrated that 84.3% of the strains have a wild-type SpeB protease phenotype. The availability of whole-genome sequence data allowed us to determine the relative frequencies of mutations in genes implicated in SpeB production. The most abundantly mutated genes were direct transcription regulators. We also sequenced the genomes of 2,954 GAS isolates recovered from nonhuman primates with experimental necrotizing fasciitis. No mutations that would result in a SpeB-deficient phenotype were identified. Taken together, these data unambiguously demonstrate that the great majority of GAS strains recovered from infected humans secrete wild-type levels of SpeB protease activity. Our data confirm the important role of SpeB in GAS pathogenesis and help end a long-standing controversy.

Comparative genomics of Streptococcus pyogenes M1 isolates differing in virulence and propensity to cause systemic infection in mice

Streptococcus pyogenes serotype M1 is a frequent cause of severe infections in humans. Some M1 isolates are pathogenic in mice and used in studies on infection pathogenesis. We observed marked differences in murine infections caused by M1 strain SF370, 5448, 5448AP or AP1 which prompted us to sequence the whole genome of isolates 5448 and AP1 for comparative analysis. Strain 5448 is known to acquire inactivating mutations in the CovRS two-component system during mouse infection, producing hypervirulent progeny such as 5448AP. Isolates AP1 and 5448AP, more than 5448, caused disseminating infections that became systemic and lethal. SF370 was not pathogenic. Phages caused gross genetic differences and increased the gene content of AP1 by 8% as compared to 5448 and SF370. Each of six examined M1 genomes contained two CRISPR-Cas systems. Phage insertion destroyed a type II CRISPR-Cas system in AP1 and other strains of serotypes M1, M3, M6 and M24, but not in M1 strains 5448, SF370, MGAS5005, A20 or M1 476. A resulting impaired defence against invading genetic elements could have led to the wealth of phages in AP1. AP1 lacks genetic features of the MGAS5005-like clonal complex including the streptodornase that drives selection for hypervirulent clones with inactivated CovRS system. Still, inactivating mutations in covS were a common genetic feature of AP1 and the MGAS5005-like isolate 5448AP. Abolished expression of the cysteine proteinase SpeB, due to CovRS inactivation could be a common cause for hypervirulence of the two isolates. Moreover, an additional protein H-coding gene and a mutation in the regulator gene rofA distinguished AP1 form other M1 isolates. In conclusion, hypervirulence of S. pyogenes M1 in mice is not limited to the MGAS5005-like genotype.

Disease manifestations and pathogenic mechanisms of Group A Streptococcus

Streptococcus pyogenes, also known as group A Streptococcus (GAS), causes mild human infections such as pharyngitis and impetigo and serious infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. Furthermore, repeated GAS infections may trigger autoimmune diseases, including acute poststreptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease. Combined, these diseases account for over half a million deaths per year globally. Genomic and molecular analyses have now characterized a large number of GAS virulence determinants, many of which exhibit overlap and redundancy in the processes of adhesion and colonization, innate immune resistance, and the capacity to facilitate tissue barrier degradation and spread within the human host. This improved understanding of the contribution of individual virulence determinants to the disease process has led to the formulation of models of GAS disease progression, which may lead to better treatment and intervention strategies. While GAS remains sensitive to all penicillins and cephalosporins, rising resistance to other antibiotics used in disease treatment is an increasing worldwide concern. Several GAS vaccine formulations that elicit protective immunity in animal models have shown promise in nonhuman primate and early-stage human trials. The development of a safe and efficacious commercial human vaccine for the prophylaxis of GAS disease remains a high priority.

Disease manifestations and pathogenic mechanisms of Group A Streptococcus

Streptococcus pyogenes, also known as group A Streptococcus (GAS), causes mild human infections such as pharyngitis and impetigo and serious infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. Furthermore, repeated GAS infections may trigger autoimmune diseases, including acute poststreptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease. Combined, these diseases account for over half a million deaths per year globally. Genomic and molecular analyses have now characterized a large number of GAS virulence determinants, many of which exhibit overlap and redundancy in the processes of adhesion and colonization, innate immune resistance, and the capacity to facilitate tissue barrier degradation and spread within the human host. This improved understanding of the contribution of individual virulence determinants to the disease process has led to the formulation of models of GAS disease progression, which may lead to better treatment and intervention strategies. While GAS remains sensitive to all penicillins and cephalosporins, rising resistance to other antibiotics used in disease treatment is an increasing worldwide concern. Several GAS vaccine formulations that elicit protective immunity in animal models have shown promise in nonhuman primate and early-stage human trials. The development of a safe and efficacious commercial human vaccine for the prophylaxis of GAS disease remains a high priority.

Streptococcal superantigens: categorization and clinical associations

Superantigens are key virulence factors in the immunopathogenesis of invasive disease caused by group A streptococcus. These protein exotoxins have also been associated with severe group C and group G streptococcal infections. A number of novel streptococcal superantigens have recently been described with some resulting confusion in their classification. In addition to clarifying the nomenclature of streptococcal superantigens and proposing guidelines for their categorization, this review summarizes the evidence supporting their involvement in various clinical diseases including acute rheumatic fever.

Cysteine proteinase SpeB from Streptococcus pyogenes - a potent modifier of immunologically important host and bacterial proteins

Group A streptococcus (Streptococcus pyogenes) is an exclusively human pathogen that causes a wide spectrum of diseases ranging from pharyngitis, to impetigo, to toxic shock, to necrotizing fasciitis. The diversity of these disease states necessitates that S. pyogenes possess the ability to modulate both the innate and adaptive immune responses. SpeB, a cysteine proteinase, is the predominant secreted protein from S. pyogenes. Because of its relatively indiscriminant specificity, this enzyme has been shown to degrade the extracellular matrix, cytokines, chemokines, complement components, immunoglobulins, and serum protease inhibitors, to name but a few of the known substrates. Additionally, SpeB regulates other streptococcal proteins by degrading them or releasing them from the bacterial surface. Despite the wealth of literature on putative SpeB functions, there remains much controversy about this enzyme because many of reported activities would produce contradictory physiological results. Here we review all known host and bacterial protein substrates for SpeB, their cleavage sites, and discuss the role of this enzyme in streptococcal pathogenesis based on the current literature.

Gene repertoire evolution of Streptococcus pyogenes inferred from phylogenomic analysis with Streptococcus canis and Streptococcus dysgalactiae

Streptococcus pyogenes, is an important human pathogen classified within the pyogenic group of streptococci, exclusively adapted to the human host. Our goal was to employ a comparative evolutionary approach to better understand the genomic events concomitant with S. pyogenes human adaptation. As part of ascertaining these events, we sequenced the genome of one of the potential sister species, the agricultural pathogen S. canis, and combined it in a comparative genomics reconciliation analysis with two other closely related species, Streptococcus dysgalactiae and Streptococcus equi, to determine the genes that were gained and lost during S. pyogenes evolution. Genome wide phylogenetic analyses involving 15 Streptococcus species provided convincing support for a clade of S. equi, S. pyogenes, S. dysgalactiae, and S. canis and suggested that the most likely S. pyogenes sister species was S. dysgalactiae. The reconciliation analysis identified 113 genes that were gained on the lineage leading to S. pyogenes. Almost half (46%) of these gained genes were phage associated and 14 showed significant matches to experimentally verified bacteria virulence factors. Subsequent to the origin of S. pyogenes, over half of the phage associated genes were involved in 90 different LGT events, mostly involving different strains of S. pyogenes, but with a high proportion involving the horse specific pathogen S. equi subsp. equi, with the directionality almost exclusively (86%) in the S. pyogenes to S. equi direction. Streptococcus agalactiae appears to have played an important role in the evolution of S. pyogenes with a high proportion of LGTs originating from this species. Overall the analysis suggests that S. pyogenes adaptation to the human host was achieved in part by (i) the integration of new virulence factors (e.g. speB, and the sal locus) and (ii) the construction of new regulation networks (e.g. rgg, and to some extent speB).

Molecular markers for the study of streptococcal epidemiology

Diseases caused by Streptococcus pyogenes (Group A streptococcus, GAS) range from superficial infections such as pharyngitis and impetigo to potentially fatal rheumatic heart disease and invasive disease. Studies spanning emm-typing surveillance to population genomics are providing new insights into the epidemiology, pathogenesis, and biology of this organism. Such studies have demonstrated the differences that exist in the epidemiology of streptococcal disease between developing and developed nations. In developing nations, where streptococcal disease is endemic, the diversity of GAS emm-types circulating is much greater than that found in developed nations. An association between emm-type and disease, as observed in developed countries is also lacking. Intriguingly, comparative genetic studies suggest that emm-type is not always a good predictor of the evolutionary relatedness of geographically distant isolates. A view of GAS as a highly dynamic organism, in possession of a core set of virulence genes that contribute to host niche specialization and common pathogenic processes, augmented by accessory genes that change the relative virulence of specific lineages is emerging. Our inability to definitively identify genetic factors that contribute to specific disease outcome underscores the complex nature of streptococcal diseases.

Cysteine proteinase SpeB from Streptococcus pyogenes - a potent modifier of immunologically important host and bacterial proteins

Group A streptococcus (Streptococcus pyogenes) is an exclusively human pathogen that causes a wide spectrum of diseases ranging from pharyngitis, to impetigo, to toxic shock, to necrotizing fasciitis. The diversity of these disease states necessitates that S. pyogenes possess the ability to modulate both the innate and adaptive immune responses. SpeB, a cysteine proteinase, is the predominant secreted protein from S. pyogenes. Because of its relatively indiscriminant specificity, this enzyme has been shown to degrade the extracellular matrix, cytokines, chemokines, complement components, immunoglobulins, and serum protease inhibitors, to name but a few of the known substrates. Additionally, SpeB regulates other streptococcal proteins by degrading them or releasing them from the bacterial surface. Despite the wealth of literature on putative SpeB functions, there remains much controversy about this enzyme because many of reported activities would produce contradictory physiological results. Here we review all known host and bacterial protein substrates for SpeB, their cleavage sites, and discuss the role of this enzyme in streptococcal pathogenesis based on the current literature.

Streptococcus pyogenes bacteraemia, emm types and superantigen profiles

The aim of this study was to investigate the emm types and superantigen profiles of bacteraemic group A streptococcal (GAS; Streptococcus pyogenes) isolates and to detect possible associations between the molecular characteristics of isolates and the clinical presentations of disease. In this population-based study, 87 bacteraemic GAS isolates from adult patients in Pirkanmaa Health District (HD), Finland, during the period 1995-2004 were emm typed and genotyped for superantigen (SAg) profiles. The epidemiological and clinical data of the patients were analysed with the microbiological characterisation data. Among the 87 isolates, 18 different emm types were found. emm1, emm28 and emm81 were the three most common types, covering 52% of isolates. The prevalence of specific emm types showed high variability during the 10-year study period. We could not find any association between the emm type and clinical features of bacteraemic infection, such as underlying diseases, disease manifestations or case fatality. Of nine superantigen genes examined, speA and speC were identified in 20 and 30% of the strains, respectively. No association was found between disease manifestation and the presence of single superantigen genes. The 26-valent GAS vaccine would have covered only 62% of isolates causing invasive disease in Pirkanmaa HD during the study period.

Comparative genomic analysis of the Streptococcus dysgalactiae species group: gene content, molecular adaptation, and promoter evolution

Comparative genomics of closely related bacterial species with different pathogenesis and host preference can provide a means of identifying the specifics of adaptive differences. Streptococcus dysgalactiae (SD) is comprised of two subspecies: S. dysgalactiae subsp. equisimilis is both a human commensal organism and a human pathogen, and S. dysgalactiae subsp. dysgalactiae is strictly an animal pathogen. Here, we present complete genome sequences for both taxa, with analyses involving other species of Streptococcus but focusing on adaptation in the SD species group. We found little evidence for enrichment in biochemical categories of genes carried by each SD strain, however, differences in the virulence gene repertoire were apparent. Some of the differences could be ascribed to prophage and integrative conjugative elements. We identified approximately 9% of the nonrecombinant core genome to be under positive selection, some of which involved known virulence factors in other bacteria. Analyses of proteomes by pooling data across genes, by biochemical category, clade, or branch, provided evidence for increased rates of evolution in several gene categories, as well as external branches of the tree. Promoters were primarily evolving under purifying selection but with certain categories of genes evolving faster. Many of these fast-evolving categories were the same as those associated with rapid evolution in proteins. Overall, these results suggest that adaptation to changing environments and new hosts in the SD species group has involved the acquisition of key virulence genes along with selection of orthologous protein-coding loci and operon promoters.

Epidemiology of invasive Streptococcus pyogenes disease in Germany during 2003-2007

A nationwide laboratory-based surveillance study of invasive Streptococcus pyogenes infections was conducted in Germany. Invasive isolates (n=586) were obtained between 2003 and 2007. Most isolates were obtained from blood (53.9%) or skin lesions (17.6%). The most common emm types were emm 1 (30.5%), emm 28 (18.3%) and emm 3 (9.6%). Overall, speA was positive in 45.9%, speC in 44.7% and ssa in 14.8% of isolates. SpeA was common in emm type 1 (100%) and emm type 3 (96.4%), whereas speC was often observed in emm type 28 (93.5%). The most frequent clinical manifestations included sepsis (40.1%), necrotizing fasciitis (20.8%) and streptococcal toxic shock syndrome (16.6%). All isolates were susceptible to penicillin G, cefotaxime and levofloxacin. Tetracycline shows the highest rate of resistant or intermediate isolates with 11.6%, followed by clarithromycin (5.5%) and clindamycin (1.2%). The most prominent trend is the reduction of tetracycline-nonsusceptible isolates from 18.6% in 2003 to 8.9% in 2007.

A naturally occurring Rgg variant in serotype M3 Streptococcus pyogenes does not activate speB expression due to altered specificity of DNA binding

The transcriptional regulator Rgg of Streptococcus pyogenes is essential for expression of the secreted cysteine protease SpeB. Although all isolates of S. pyogenes possess the speB gene, not all of them produce the protein in vitro. In a murine model of infection, the absence of SpeB production is associated with invasive disease. We speculated that naturally occurring mutations in rgg, which would also abrogate SpeB production, may be present in invasive isolates of S. pyogenes. Examination of the inferred Rgg sequences available in public databases revealed that the rgg gene in strain MGAS315 (a serotype M3 strain associated with invasive disease) encodes a proline at amino acid position 103 (Rgg(103P)); in contrast, all other strains encode a serine at this position (Rgg(103S)). A caseinolytic assay and Western blotting indicated that strain MGAS315 does not produce SpeB in vitro. Gene-swapping experiments showed that the rgg gene of MGAS315 is solely responsible for the lack of SpeB expression. In contrast to Rgg(103S), Rgg(103P) does not bind to the speB promoter in gel shift assays, which correlates with a lack of speB expression. Despite its inability to activate speB expression, Rgg(103P) retains the ability to bind to DNA upstream of norA and to influence its expression. Overall, this study illustrates how variation at the rgg locus may contribute to the phenotypic diversity of S. pyogenes.

emm1/sequence type 28 strains of group A streptococci that express covR at early stationary phase are associated with increased growth and earlier SpeB secretion

Streptococcus pyogenes (group A streptococcus [GAS]) is a versatile human pathogen, and emm1/sequence type 28 (ST28) is the most frequently isolated type from GAS infections. The emm1/ST28 strain is associated with necrotizing fasciitis and streptococcal toxic shock syndrome. Growth-phase regulation is one of the important regulatory mechanisms in GAS, which controls gene expression at restricted phases of growth. CovRS, a two-component regulatory system, is considered the regulator of streptococcal pyrogenic exotoxin B (SpeB) and is thought to be activated in the exponential phase of growth. In the present study, Northern hybridization analysis showed that 52% of the analyzed GAS strains expressed covR at the exponential phase, but 48% of the strains expressed covR at the early stationary phase of growth. Strains transcribing covR at the early stationary phase showed better growth and earlier SpeB expression than the other group of strains. Multilocus sequence typing and pulsed-field gel electrophoresis analysis showed only emm1/ST28 strains (which comprise a clonal cluster) were expressing covR at the early stationary phase of growth, indicating that emm1/ST28 strains have special characteristics which may be related to their worldwide distribution.

Group A streptococcal puerperal sepsis: initial characterization of virulence factors in association with clinical parameters

Group A beta-hemolytic streptococcus (GAS) is an uncommon but potentially fatal source of postpartum infection. Pathogenesis in invasive GAS infections has been linked to bacterial virulence factors. In this study, we sought to provide an initial description of potential virulence factors in association with puerperal morbidity by virtue of specific M-protein type antigens. Women with confirmed GAS puerperal infection in the Salt Lake City region were prospectively identified over a 6-year interval (1991-1997). From this cohort, GAS isolates were analyzed with respect to M-serotype and presence of genes encoding the Streptococcal Pyogenic Exotoxins A and B (SPE-A and SPE-B). Bacterial isolates from 18 subjects with GAS puerperal infection underwent M-serotyping and PCR-based genotyping for the speA and speB genes. Among these, 8/18 subjects manifest criteria of severe disease. All 18 isolate strains expressed speB; 6/18 isolates expressed speA. Of the M-serotypes, 8/8 severe disease isolates expressed M-types 1 (N=3) or 28 (N=5). Pulse-field gel electrophoresis did not indicate an outbreak strain among similar isolates. We conclude that in this initial characterization, morbidity among women with GAS puerperal infection is associated with M-types 1 and 28, but not speB genotype.

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.

SpeB of Streptococcus pyogenes differentially modulates antibacterial and receptor activating properties of human chemokines

Background

CXC chemokines are induced by inflammatory stimuli in epithelial cells and some, like MIG/CXCL9, IP–10/CXCL10 and I–TAC/CXCL11, are antibacterial for Streptococcus pyogenes.

Methodology/Principal Findings

SpeB from S. pyogenes degrades a wide range of chemokines (i.e. IP10/CXCL10, I-TAC/CXCL11, PF4/CXCL4, GROα/CXCL1, GROβ/CXCL2, GROγ/CXCL3, ENA78/CXCL5, GCP-2/CXCL6, NAP-2/CXCL7, SDF-1/CXCL12, BCA-1/CXCL13, BRAK/CXCL14, SRPSOX/CXCL16, MIP-3α/CCL20, Lymphotactin/XCL1, and Fractalkine/CX3CL1), has no activity on IL-8/CXCL8 and RANTES/CCL5, partly degrades SRPSOX/CXCL16 and MIP-3α/CCL20, and releases a 6 kDa CXCL9 fragment. CXCL10 and CXCL11 loose receptor activating and antibacterial activities, while the CXCL9 fragment does not activate the receptor CXCR3 but retains its antibacterial activity.

Conclusions/Significance

SpeB destroys most of the signaling and antibacterial properties of chemokines expressed by an inflamed epithelium. The exception is CXCL9 that preserves its antibacterial activity after hydrolysis, emphasizing its role as a major antimicrobial on inflamed epithelium.

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.

Genome sequence of a nephritogenic and highly transformable M49 strain of Streptococcus pyogenes

The 1,815,783-bp genome of a serotype M49 strain of Streptococcus pyogenes (group A streptococcus [GAS]), strain NZ131, has been determined. This GAS strain (FCT type 3; emm pattern E), originally isolated from a case of acute post-streptococcal glomerulonephritis, is unusually competent for electrotransformation and has been used extensively as a model organism for both basic genetic and pathogenesis investigations. As with the previously sequenced S. pyogenes genomes, three unique prophages are a major source of genetic diversity. Two clustered regularly interspaced short palindromic repeat (CRISPR) regions were present in the genome, providing genetic information on previous prophage encounters. A unique cluster of genes was found in the pathogenicity island-like emm region that included a novel Nudix hydrolase, and, further, this cluster appears to be specific for serotype M49 and M82 strains. Nudix hydrolases eliminate potentially hazardous materials or prevent the unbalanced accumulation of normal metabolites; in bacteria, these enzymes may play a role in host cell invasion. Since M49 S. pyogenes strains have been known to be associated with skin infections, the Nudix hydrolase and its associated genes may have a role in facilitating survival in an environment that is more variable and unpredictable than the uniform warmth and moisture of the throat. The genome of NZ131 continues to shed light upon the evolutionary history of this human pathogen. Apparent horizontal transfer of genetic material has led to the existence of highly variable virulence-associated regions that are marked by multiple rearrangements and genetic diversification while other regions, even those associated with virulence, vary little between genomes. The genome regions that encode surface gene products that will interact with host targets or aid in immune avoidance are the ones that display the most sequence diversity. Thus, while natural selection favors stability in much of the genome, it favors diversity in these regions.

Rise and persistence of global M1T1 clone of Streptococcus pyogenes

The resurgence of severe invasive group A streptococcal infections in the 1980s is a typical example of the reemergence of an infectious disease. We found that this resurgence is a consequence of the diversification of particular strains of the bacteria. Among these strains is a highly virulent subclone of serotype M1T1 that has exhibited unusual epidemiologic features and virulence, unlike all other streptococcal strains. This clonal strain, commonly isolated from both noninvasive and invasive infection cases, is most frequently associated with severe invasive diseases. Because of its unusual prevalence, global spread, and increased virulence, we investigated the unique features that likely confer its unusual properties. In doing so, we found that the increased virulence of this clonal strain can be attributed to its diversification through phage mobilization and its ability to sense and adapt to different host environments; accordingly, the fittest members of this diverse bacterial community are selected to survive and invade host tissue.

EndoS from Streptococcus pyogenes is hydrolyzed by the cysteine proteinase SpeB and requires glutamic acid 235 and tryptophans for IgG glycan-hydrolyzing activity

Background

The endoglycosidase EndoS and the cysteine proteinase SpeB from the human pathogen Streptococcus pyogenes are functionally related in that they both hydrolyze IgG leading to impairment of opsonizing antibodies and thus enhance bacterial survival in human blood. In this study, we further investigated the relationship between EndoS and SpeB by examining their in vitro temporal production and stability and activity of EndoS. Furthermore, theoretical structure modeling of EndoS combined with site-directed mutagenesis and chemical blocking of amino acids was used to identify amino acids required for the IgG glycan-hydrolyzing activity of EndoS.

Results

We could show that during growth in vitro S. pyogenes secretes the IgG glycan-hydrolyzing endoglycosidase EndoS prior to the cysteine proteinase SpeB. Upon maturation SpeB hydrolyzes EndoS that then loses its IgG glycan-hydrolyzing activity. Sequence analysis and structural homology modeling of EndoS provided a basis for further analysis of the prerequisites for IgG glycan-hydrolysis. Site-directed mutagenesis and chemical modification of amino acids revealed that glutamic acid 235 is an essential catalytic residue, and that tryptophan residues, but not the abundant lysine or the single cysteine residues, are important for EndoS activity.

Conclusion

We present novel information about the amino acid requirements for IgG glycan-hydrolyzing activity of the immunomodulating enzyme EndoS. Furthermore, we show that the cysteine proteinase SpeB processes/degrades EndoS and thus emphasize the importance of the SpeB as a degrading/processing enzyme of proteins from the bacterium itself.

Clinical and epidemiological aspects of invasive Streptococcus pyogenes infections in Denmark during 2003 and 2004

Active surveillance of invasive group A streptococcal (GAS) infections was conducted in Denmark during 2003 and 2004 as a part of the Strep-EURO initiative. The main objective was to improve understanding of the epidemiology of invasive GAS disease in Denmark. During the 2 years, 278 cases were reported, corresponding to a mean annual incidence of 2.6 cases per 100,000 inhabitants. The vast majority of isolates, 253 (91%), were from blood, with the remaining 25 (9%) being from cerebrospinal fluid, joints, or other normally sterile sites. The mean case fatality rate (CFR) was 20%, with the rate being higher in patients more than 70 years of age (36.5%). For streptococcal toxic shock syndrome (STSS) and necrotizing fasciitis the CFRs were 53% and 25%, respectively. Out of 16 T types recorded, three predominated: T28 (23%), T1 (22%), and the cluster T3/13/B3264 (14%). Among 29 different emm types, emm28 and emm1 accounted for 51% of strains, followed by emm3 (11%), emm89 (7%), and emm12 (5.5%). Low resistance rates were detected for macrolide-lincosamide-streptogramin B (MLS(B)) antibiotics (3%) and tetracycline (8%); two isolates exhibited coresistance to tetracycline and macrolides. Of nine pyrogenic exotoxin (superantigen) genes examined, speA and speC were identified in 58% and 40% of the strains, respectively; either of the genes was present in all strains causing STSS. Most strains harbored speG (99%). ssa was present in 14% of the isolates only. In Denmark, as in comparable countries, GAS invasive disease shows a sustained, high endemicity, with involvement of both established and emerging streptococcal emm and T types.

Molecular and Clinical Characteristics of Invasive Group A Streptococcal Infection in Sweden

BACKGROUND

The incidence and severity of invasive group A streptococcal infection demonstrate great variability over time, which at least, in part, seems to be related to group A streptococcal type distribution among the human population.

METHODS

An enhanced surveillance study of invasive group A streptococcal infection (746 isolates) was performed in Sweden from April 2002 through December 2004. Noninvasive isolates from either the throat or skin (773 isolates) were collected in parallel for comparison. Clinical and epidemiological data were obtained from 88% of patients with invasive disease and were related to isolate characteristics, including T type, emm sequence type, and the presence of 9 superantigen genes, as well as pulsed-field gel electrophoresis pattern comparisons of selected isolates.

RESULTS

The annual incidence was 3.0 cases per 100,000 population. Among the patients with invasive disease, 11% developed streptococcal toxic shock syndrome, and 9.5% developed necrotizing fasciitis. The overall case-fatality rate was 14.5%, and 39% of the patients with streptococcal toxic shock syndrome died (P<.001). The T3/13/B3264 cluster accounted for 33% of invasive and 25% of noninvasive isolates. Among this most prevalent type cluster, emm types 89 and 81 dominated. Combined results from pulsed-field gel electrophoresis, emm typing, and superantigen gene profiling identified subgroups within specific emm types that are significantly more prone to cause invasive disease than were other isolates of the same type.

CONCLUSIONS

This study revealed a changing epidemiology of invasive group A streptococcal infection in Sweden, with emergence of new emm types that were previously not described. The results also suggest that some clones may be particularly prone to cause invasive disease.

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.

Survey of phenotypic and genetic features of streptococcus pyogenes strains isolated in Northwest Italy

Streptococcus pyogenes (group A Streptococcus [GAS]) is an important pathogen whose virulence is related to the production of exotoxins and the presence of particular surface components. One hundred eighty-two GAS strains were collected in northwestern Italy between 1994 and 2002 and analyzed for phenotypic characteristics (opacity factor, proteolyic activity, and antimicrobial susceptibility) and by polymerase chain reaction for the presence of genes responsible for the production of exotoxins implicated in pathogenesis speA and speF and of prtF(1) (encoding fibronectin-binding protein F1). All strains were speF positive and 19.2% were speA positive and prtF(1) negative, whereas the prtF(1) gene was identified in 39.5% of the other strains. Of these, approximately half revealed the same pulse-field gel electrophoresis (PFGE) pattern but differed in both speA gene and macrolide resistance.

Involvement of streptococcal mitogenic exotoxin Z in streptococcal toxic shock syndrome

We report a nonfatal case of streptococcal toxic shock syndrome (STSS) caused by a Streptococcus pyogenes emm118 strain encoding a novel variant of streptococcal mitogenic exotoxin Z (SMEZ-34). This variant was responsible for the major mitogenic activity in the cell culture supernatant. Patient sera showed seroconversion toward SMEZ, implying a role for this toxin in STSS.

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.

Endogenous interleukin-6 plays a crucial protective role in streptococcal toxic shock syndrome via suppression of tumor necrosis factor alpha production

During a Streptococcus pyogenes infection in interleukin-6 (IL-6)-deficient mice, there is elevation of serum tumor necrosis factor alpha (TNF-alpha) levels, muscular necrosis, and death compared with infection of C57BL/6 mice. Anti-TNF-alpha monoclonal antibody treatment decreased mortality and muscular necrosis in the infected IL-6-deficient mice. These results suggest that IL-6 plays a crucial protective role via suppression of TNF-alpha production in S. pyogenes infection.

SpeB-Spi: a novel protease-inhibitor pair from Streptococcus pyogenes

This study presents evidence for a novel protease-protease inhibitor couple, SpeB-Spi, in the human pathogen Streptococcus pyogenes. The gene for the inhibitor Spi is located directly downstream of the gene for the streptococcal cysteine protease SpeB. Spi is 37% identical and 70% similar to the sequence of the SpeB propeptide, suggesting that Spi and the SpeB propeptide might bind to SpeB in an analogous manner. Secondary structure predictions and molecular modelling suggested that Spi would adopt a structure similar to the SpeB propeptide. The spi gene was co-transcribed with speB on the 1.7 knt and 2.2 knt transcripts previously identified for speB. The Spi protein was purified by SpeB-affinity chromatography from the S. pyogenes cytoplasm. Recombinant Spi was produced and purified, and shown to bind to SpeB and to inhibit its protease activity. Although a similar genetic arrangement of protease and inhibitor is present in staphylococci, this is the first example of an inhibitor molecule that is a structural homologue of the cognate propeptide, and which is genetically linked to the protease gene. Thus, this represents a novel system whereby bacteria may control the intracellular activity of their proteases.

The M protein is dispensable for maturation of streptococcal cysteine protease SpeB

The streptococcal pyrogenic exotoxin B (SpeB) is an important virulence factor of group A streptococci (GAS) with cysteine protease activity. Maturation of SpeB to a proteolytically active form was suggested to be dependent on cell-wall-anchored M1 protein, the major surface protein of GAS (M. Collin and A. Olsen, Mol. Microbiol. 36:1306-1318, 2000). Collin and Olsen showed that mutant GAS strains expressing truncated M protein secrete a conformationally different form of unprocessed SpeB with no proteolytic activity. Alternatively, we hypothesized that a truncated M protein may interfere with processing of this secreted protease, and therefore we tested cysteine protease activity in genetically defined mutant strains that express either no M protein or membrane-anchored M protein with an in-frame deletion of the AB repeat region. Measurements of SpeB activity by cleavage of a substrate n-benzoyl-Pro-Phe-Arg-p-nitroanilide hydrochloride showed that the proteolytic activities in culture supernatants of both mutants were similar to those from the wild-type strain. In addition, Western blot analysis of culture supernatants showed that SpeB expression and processing to a mature form was unaffected by either deletion mutation. Therefore, we conclude that M protein is not required for maturation of the streptococcal cysteine protease SpeB.

Histopathologic changes in kidney and liver correlate with streptococcal pyrogenic exotoxin B production in the mouse model of group A streptococcal infection

Previous studies show that isogenic mutants deficient in streptococcal pyrogenic exotoxin B (SPE B) cause less mortality and skin tissue damage than wild-type strains of Streptococcus pyogenes when inoculated into mice via an air pouch. In this study, the growth and dissemination of bacteria, pathologic changes in various organs, and their correlation with SPE B production were examined. Bacterial numbers in the air pouch from wild-type strain NZ131-infected mice increased at 48 h, while those from speB mutant SW510-infected mice continuously reduced. Mice infected with NZ131 developed bacteremia and greater dissemination in the kidney, liver, and spleen; those infected with SW510 showed either no or slight bacteremia and dissemination. Co-inoculation of SW510 with recombinant SPE B showed a higher bacterial count in the air pouch, bacteremia, and organ dissemination compared to co-inoculation with a C192S mutant lacking protease activity. The histopathologic changes examined showed lesions in kidney and liver in the NZ131-infected but not in SW510-infected mice. The elevation in sera of BUN, AST, and ALT correlated positively with renal and liver impairment. Taken together, SPE B produced during S. pyogenes infection plays a pathogenic role. A direct effect of SPE B on vessel permeability change was also demonstrated.

Mouse skin passage of Streptococcus pyogenes results in increased streptokinase expression and activity

The plasminogen activator streptokinase has been proposed to be a key component of a complex mechanism that promotes skin invasion by Streptococcus pyogenes. This study was designed to compare ska gene message and protein levels in wild-type M1 serotype isolate 1881 and a more invasive variant recovered from the spleen of a lethally infected mouse. M1 isolates selected for invasiveness demonstrated enhanced levels of active plasminogen activator activity in culture. This effect was due to a combination of increased expression of the ska gene and decreased expression of the speB gene. The speB gene product, SpeB, was found to efficiently degrade streptokinase in vitro.

Plasminogen binding by group A streptococcal isolates from a region of hyperendemicity for streptococcal skin infection and a high incidence of invasive infection

Reports of resurgence in invasive group A streptococcal (GAS) infections come mainly from affluent populations with infrequent exposure to GAS. In the Northern Territory (NT) of Australia, high incidence of invasive GAS disease is secondary to endemic skin infection, serotype M1 clones are rare in invasive infection, the diversity and level of exposure to GAS strains are high, and no particular strains dominate. Expression of a plasminogen-binding GAS M-like protein (PAM) has been associated with skin infection in isolates elsewhere (D. Bessen, C. M. Sotir, T. M. Readdy, and S. K. Hollingshead, J. Infect. Dis. 173:896-900, 1996), and subversion of the host plasminogen system by GAS is thought to contribute to invasion in animal models. Here, we describe the relationship between plasminogen-binding capacity of GAS isolates, PAM genotype, and invasive capacity in 29 GAS isolates belonging to 25 distinct strains from the NT. In the presence of fibrinogen and streptokinase, invasive isolates bound more plasminogen than isolates from uncomplicated infections (P < or = 0.004). Only PAM-positive isolates bound substantial levels of plasminogen by a fibrinogen-streptokinase-independent pathway (direct binding). Despite considerable amino acid sequence variation within the A1 repeat region of PAM where the plasminogen-binding domain maps, the critical lysine residue was conserved.

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.

Mass antibiotic treatment for group A streptococcus outbreaks in two long-term care facilities

Outbreaks of invasive infections caused by group A β-hemolytic streptococcus (GAS) may occur in long-term care settings and are associated with a high case-fatality rate in debilitated adults. Targeted antibiotic treatment only to residents and staff known to be at specific risk of GAS may be an ineffective outbreak control measure. We describe two institutional outbreaks in which mass antibiotic treatment was used as a control measure. In the first instance, mass treatment was used after targeted antibiotic treatment was not successful. In the second instance, mass treatment was used to control a rapidly evolving outbreak with a high case-fatality rate. Although no further clinical cases were seen after the introduction of mass antibiotic treatment, persistence of the outbreak strain was documented in one institution >1 year after cases had ceased. Strain persistence was associated with the presence of a chronically colonized resident and poor infection control practices.