Staging of the baboon response to group A streptococci administered intramuscularly: a descriptive study of the clinical symptoms and clinical chemical response patterns

Reference Intervals and Clinical Utility of Acute Phase Proteins and Serum Proteins Electrophoresis in the Hamadryas Baboon (Papio hamadryas)

Measurements of specific acute phase proteins (APP) and protein electrophoresis (EPH) fractions have been widely used to better assess the health of species under managed care across numerous taxa. To date, APP assays have not been validated in the hamadryas baboon (Papio hamadryas), and reference intervals have not yet been established. This information is critical for the interpretation of APP and EPH measurements used in the diagnosis of inflammatory diseases during routine veterinary care of this species. To obtain this information, banked serum samples from hamadryas baboons of various age, sex, and health status, under managed care at the North Carolina Zoo, were analyzed. A small pilot study found significantly higher serum amyloid A (SAA) and C-reactive protein (CRP) but not haptoglobin in baboons with acute inflammation compared to healthy counterparts, so these two APPs were investigated further. Reagents for serum amyloid A (SAA) and C-reactive protein (CRP) were validated, although differences in CRP reagents were observed. Based on the results of this study, SAA and CRP were defined as major APPs that were significantly increased in baboons with active inflammation or infection compared to healthy conspecifics. Baboons with acute inflammation additionally had significantly higher gamma globulins compared to healthy baboons. Although mean albumin concentrations were lower in baboons with acute inflammation, the difference from healthy baboons was not statistically significant. This study identifies SAA, CRP, and EPH as useful tools in the diagnosis of inflammatory disease in the hamadryas baboon and establishes reference intervals to aid in the future veterinary care of this species.

Murine Soft Tissue Infection Model to Study Group A Streptococcus (GAS) Pathogenesis in Necrotizing Fasciitis

Group A streptococcus (GAS) necrotizing fasciitis (NF) causes high morbidity and mortality despite prompt intravenous administration of antibiotics, surgical soft-tissue debridement, and supportive treatment in the intensive care unit. Since there is no effective vaccine against GAS infections, a comprehensive understanding of NF pathogenesis is required to design more efficient treatments. To increase our understanding of NF pathogenesis, we need a reliable animal model that mirrors, at least in part, the infectious process in humans. This chapter describes a reliable murine model of human NF that mimics the histopathology observed in humans, namely the destruction of soft tissue, a paucity of infiltrating neutrophils, and the presence of many gram-positive cocci at the center of the infection.

Pathology Associated With Streptococcus spp. Infection in Baboons (Papio spp.)

Streptococcus spp. are a source of morbidity and mortality in captive nonhuman primate populations. However, little is known about the lesions associated with naturally occurring streptococcal infections in baboons (Papio spp.). The pathology database of the Southwest National Primate Research Center was searched for all baboon autopsies from 1988 to 2018 in which Streptococcus spp. were cultured. Baboons on experimental protocol were excluded. The gross autopsy and histopathology reports were reviewed. Archived specimens were retrieved and reviewed as needed for confirmation or clarification. Fifty-six cultures were positive for Streptococcus spp. in 54 baboons with evidence of bacterial infection. Associated gross lesions included purulent exudate, fibrinous to fibrous adhesions, hemorrhage, mucosal thickening, organomegaly, and abscessation. Histologic lesions included suppurative inflammation, abscessation, necrosis, hemorrhage, fibrin accumulation, and thrombosis. Lungs and pleura (n = 31) were the most commonly infected organ followed by the central nervous system (n = 16), spleen (n = 15), soft tissues (n = 12), air sacs, liver, peritoneum, adrenal glands, heart, lymph nodes, uterus, kidneys, biliary system, bones, ears, umbilical structures, mammary glands, pancreas, placenta, and salivary glands. Infections by non-β-hemolytic Streptococcus spp. predominated in the lungs and air sacs; the most common isolate was Streptococcus pneumoniae. Infections by β-hemolytic Streptococcus spp. predominated in the soft tissues and reproductive tract. Naturally occurring β-hemolytic and non-β-hemolytic Streptococcus spp. infections cause morbidity and mortality in captive baboon populations. The lesions associated with streptococcal infection are similar to those reported in human infection. Thus, the baboon may represent an underutilized model for studying Streptococcus spp. as pathogens.

Nonhuman primate species as models of human bacterial sepsis

Sepsis involves a disordered host response to systemic infection leading to high morbidity and mortality. Despite intense research, targeted sepsis therapies beyond antibiotics have remained elusive. The cornerstone of sepsis research is the development of animal models to mimic human bacterial infections and test novel pharmacologic targets. Nonhuman primates (NHPs) have served as an attractive, but expensive, animal to model human bacterial infections due to their nearly identical cardiopulmonary anatomy and physiology, as well as host response to infection. Several NHP species have provided substantial insight into sepsis-mediated inflammation, endothelial dysfunction, acute lung injury, and multi-organ failure. The use of NHPs has usually focused on translating therapies from early preclinical models to human clinical trials. However, despite successful sepsis interventions in NHP models, there are still no FDA-approved sepsis therapies. This review highlights major NHP models of bacterial sepsis and their relevance to clinical medicine.

Treatment for bacterial sepsis remains limited beyond the use of antibiotics. Lingye Chen, Karen Welty-Wolf, and Bryan Kraft review nonhuman primate models of sepsis and highlight their advantages and limitations compared to other preclinical models.

Streptolysin-induced endoplasmic reticulum stress promotes group A Streptococcal host-associated biofilm formation and necrotising fasciitis

Group A Streptococcus (GAS) is a human pathogen that causes infections ranging from mild to fulminant and life-threatening. Biofilms have been implicated in acute GAS soft-tissue infections such as necrotising fasciitis (NF). However, most in vitro models used to study GAS biofilms have been designed to mimic chronic infections and insufficiently recapitulate in vivo conditions along with the host-pathogen interactions that might influence biofilm formation. Here, we establish and characterise an in vitro model of GAS biofilm development on mammalian cells that simulates microcolony formation observed in a mouse model of human NF. We show that on mammalian cells, GAS forms dense aggregates that display hallmark biofilm characteristics including a 3D architecture and enhanced tolerance to antibiotics. In contrast to abiotic-grown biofilms, host-associated biofilms require the expression of secreted GAS streptolysins O and S (SLO, SLS) that induce endoplasmic reticulum (ER) stress in the host. In an in vivo mouse model, the streptolysin null mutant is attenuated in both microcolony formation and bacterial spread, but pretreatment of soft-tissue with an ER stressor restores the ability of the mutant to form wild-type-like microcolonies that disseminate throughout the soft tissue. Taken together, we have identified a new role of streptolysin-driven ER stress in GAS biofilm formation and NF disease progression.

Genomic Landscape of Intrahost Variation in Group A Streptococcus: Repeated and Abundant Mutational Inactivation of the fabT Gene Encoding a Regulator of Fatty Acid Synthesis

To obtain new information about Streptococcus pyogenes intrahost genetic variation during invasive infection, we sequenced the genomes of 2,954 serotype M1 strains recovered from a nonhuman primate experimental model of necrotizing fasciitis. A total of 644 strains (21.8%) acquired polymorphisms relative to the input parental strain. The fabT gene, encoding a transcriptional regulator of fatty acid biosynthesis genes, contained 54.5% of these changes. The great majority of polymorphisms were predicted to deleteriously alter FabT function. Transcriptome-sequencing (RNA-seq) analysis of a wild-type strain and an isogenic fabT deletion mutant strain found that between 3.7 and 28.5% of the S. pyogenes transcripts were differentially expressed, depending on the growth temperature (35°C or 40°C) and growth phase (mid-exponential or stationary phase). Genes implicated in fatty acid synthesis and lipid metabolism were significantly upregulated in the fabT deletion mutant strain. FabT also directly or indirectly regulated central carbon metabolism genes, including pyruvate hub enzymes and fermentation pathways and virulence genes. Deletion of fabT decreased virulence in a nonhuman primate model of necrotizing fasciitis. In addition, the fabT deletion strain had significantly decreased survival in human whole blood and during phagocytic interaction with polymorphonuclear leukocytes ex vivo We conclude that FabT mutant progeny arise during infection, constitute a metabolically distinct subpopulation, and are less virulent in the experimental models used here.

Characterization of streptococcal platelet-activating factor acetylhydrolase variants that are involved in innate immune evasion

Human pathogen group A streptococcus (GAS) has developed mechanisms to subvert innate immunity. We recently reported that the secreted esterase produced by serotype M1 GAS (SsE(M1)) reduces neutrophil recruitment by targeting platelet-activating factor (PAF). SsE(M1) and SsE produced by serotype M28 GAS (SsE(M28)) have a 37% sequence difference. This study aims at determining whether SsE(M28) is also a PAF acetylhydrolase and participates in innate immune evasion. We also examined whether SsE evolved to target PAF by characterizing the PAF acetylhydrolase (PAF-AH) activity and substrate specificity of SsE(M1), SsE(M28), SeE, the SsE homologue in Streptococcus equi, and human plasma PAF-AH (hpPAF-AH). PAF incubated with SsE(M28) or SeE was converted into lyso-PAF. SsE(M1) and SsE(M28) had kcat values of 373 s(-1) and 467 s(-1), respectively, that were ≥ 30-fold greater than that of hpPAF-AH (12 s(-1)). The comparison of SsE(M1), SsE(M28), and hpPAF-AH in kcat and Km in hydrolyzing triglycerides, acetyl esters, and PAF indicates that the SsE proteins are more potent hydrolases against PAF and have high affinity for PAF. SsE(M28) possesses much lower esterase activities against triglycerides and other esters than SsE(M1) but have similar potency with SsE(M1) in PAF hydrolysis. Deletion of sse(M28) in a covS deletion mutant of GAS increased neutrophil recruitment and reduced skin infection, whereas in trans expression of SsE(M28) in GAS reduced neutrophil infiltration and increased skin invasion in subcutaneous infection of mice. These results suggest that the SsE proteins evolved to target PAF for enhancing innate immune evasion and skin invasion.

Regulation of inhibition of neutrophil infiltration by the two-component regulatory system CovRS in subcutaneous murine infection with group A streptococcus

Hypervirulent invasive group A streptococcus (GAS) isolates inhibit neutrophil infiltration more than pharyngitis isolates do, and the molecular basis of this difference is not well understood. This study was designed to first determine whether natural null mutation of the two-component regulatory system CovRS is responsible for the enhancement of the inhibition of neutrophil recruitment seen in hypervirulent GAS. Next, we examined the role of CovRS-regulated interleukin-8/CXC chemokine peptidase (SpyCEP), C5a peptidase (ScpA), and platelet-activating factor acetylhydrolase (SsE) in the enhanced innate immune evasion. Invasive isolate MGAS5005 induces less neutrophil infiltration and produced a greater lesion area than pharyngitis isolate MGAS2221 in subcutaneous infections of mice. It is known that MGAS5005, but not MGAS2221, has a natural 1-bp deletion in the covS gene. Replacement of covS(Δ1bp) in MGAS5005 with wild-type covS resulted in the MGAS2221 phenotype. Deletion of covS from MGAS2221 resulted in the MGAS5005 phenotype. Tests of single, double, and triple deletion mutants of the MGAS5005 sse, spyCEP, and scpA genes found that SsE plays a more important role than SpyCEP and ScpA in the inhibition of neutrophil recruitment and that SsE, SpyCEP, and ScpA do not have synergistic effects on innate immune evasion by MGAS5005. Deletion of sse, but not spyCEP or scpA, of MGAS2221 enhances neutrophil recruitment. Thus, covS null mutations can cause substantial inhibition of neutrophil recruitment by enhancing the expression of the chemoattractant-degrading virulence factors, and SsE, but not SpyCEP or ScpA, is required for CovRS-regulated GAS inhibition of neutrophil infiltration.

Group A Streptococcus secreted esterase hydrolyzes platelet-activating factor to impede neutrophil recruitment and facilitate innate immune evasion

The innate immune system is the first line of host defense against invading organisms. Thus, pathogens have developed virulence mechanisms to evade the innate immune system. Here, we report a novel means for inhibition of neutrophil recruitment by Group A Streptococcus (GAS). Deletion of the secreted esterase gene (designated sse) in M1T1 GAS strains with (MGAS5005) and without (MGAS2221) a null covS mutation enhances neutrophil ingress to infection sites in the skin of mice. In trans expression of SsE in MGAS2221 reduces neutrophil recruitment and enhances skin invasion. The sse deletion mutant of MGAS5005 (Δsse^MGAS5005) is more efficiently cleared from skin than the parent strain. SsE hydrolyzes the sn-2 ester bond of platelet-activating factor (PAF), converting biologically active PAF into inactive lyso-PAF. K_M and k_cat of SsE for hydrolysis of 2-thio-PAF were similar to those of the human plasma PAF acetylhydrolase. Treatment of PAF with SsE abolishes the capacity of PAF to induce activation and chemotaxis of human neutrophils. More importantly, PAF receptor-deficient mice significantly reduce neutrophil infiltration to the site of Δsse^MGAS5005 infection. These findings identify the first secreted PAF acetylhydrolase of bacterial pathogens and support a novel GAS evasion mechanism that reduces phagocyte recruitment to sites of infection by inactivating PAF, providing a new paradigm for bacterial evasion of neutrophil responses.

GAS is a major human pathogen causing a variety of infections, including pharyngitis and necrotizing fasciitis. GAS pathogenesis is mediated by a large array of secreted and cell-surface virulence factors. However, the functions of many GAS virulence factors are poorly understood. Recently, we reported that the esterase secreted by GAS (SsE) is a CovRS (the control of virulence two component regulatory system)-regulated protective antigen and is critical for spreading in the skin and systemic dissemination of GAS in a mouse model of necrotizing fasciitis. This report presents three major findings regarding the function and functional mechanism of SsE: 1) SsE contributes to GAS inhibition of neutrophil recruitment; 2) SsE is a potent PAF acetylhydrolase and the first secreted bacterial PAF acetylhydrolase identified so far; and 3) the PAF receptor significantly contributes to neutrophil recruitment in skin GAS infection. These findings support a novel mechanism for evasion of the innate immune system by GAS that may be relevant to other infections.

Modulation of the coagulation system during severe streptococcal disease

Haemostasis is maintained by a tightly regulated coagulation system that comprises platelets, procoagulant proteins, and anticoagulant proteins. During the local and systemic response to bacterial infection, the coagulation system becomes activated, and contributes to the pathophysiological response to infection. The significant human pathogen, Streptococcus pyogenes has multiple strategies to modulate coagulation. This can range from systemic activation of the intrinsic and extrinsic pathway of coagulation to local stimulation of fibrinolysis. Such diverse effects on this host system imply a finely tuned host-bacteria interaction. The molecular mechanisms that underlie this modulation of the coagulation system are discussed in this review.

Streptolysin S-like virulence factors: the continuing sagA

Streptolysin S (SLS) is a potent cytolytic toxin and virulence factor that is produced by nearly all Streptococcus pyogenes strains. Despite a 100-year history of research on this toxin, it has only recently been established that SLS is just one of an extended family of post-translationally modified virulence factors (the SLS-like peptides) that are produced by some streptococci and other Gram-positive pathogens, such as Listeria monocytogenes and Clostridium botulinum. In this Review, we describe the identification, genetics, biochemistry and various functions of SLS. We also discuss the shared features of the virulence-associated SLS-like peptides, as well as their place within the rapidly expanding family of thiazole/oxazole-modified microcins (TOMMs).

Molecular pathogenesis of necrotizing fasciitis

Necrotizing fasciitis, also known as the flesh-eating disease, is a severe invasive infection associated with very high rates of human morbidity and mortality. It is most commonly caused by group A Streptococcus(GAS), a versatile human pathogen that causes diseases ranging in severity from uncomplicated pharyngitis (or strep throat) to life-threatening infections such as necrotizing fasciitis. Herein, we review recent discoveries bearing on the molecular pathogenesis of GAS necrotizing fasciitis. Importantly, the integration of new technologies and the development of human-relevant animal models have markedly expanded our understanding of the key pathogen-host interactions underlying GAS necrotizing fasciitis. For example, we now know that GAS organisms secrete a variety of proteases that disrupt host tissue and that these proteolytic enzymes are regulated by multiple transcriptional and posttranslational processes. This pathogenesis knowledge will be crucial to supporting downstream efforts that seek to develop novel vaccines and therapeutic agents for this serious human infection.

Functional dissection of Streptococcus pyogenes M5 protein: the hypervariable region is essential for virulence

The surface-localized M protein of Streptococcus pyogenes is a major virulence factor that inhibits phagocytosis, as determined ex vivo. Because little is known about the role of M protein in vivo we analyzed the contribution of different M protein regions to virulence, using the fibrinogen (Fg)-binding M5 protein and a mouse model of acute invasive infection. This model was suitable, because M5 is required for mouse virulence and binds mouse and human Fg equally well, as shown here. Mixed infection experiments with wild type bacteria demonstrated that mutants lacking the N-terminal hypervariable region (HVR) or the Fg-binding B-repeat region were strongly attenuated, while a mutant lacking the conserved C-repeats was only slightly attenuated. Because the HVR of M5 is not required for phagocytosis resistance, our data imply that this HVR plays a major but unknown role during acute infection. The B-repeat region is required for phagocytosis resistance and specifically binds Fg, suggesting that it promotes virulence by binding Fg. However, B-repeat mutants were attenuated even in Fg-deficient mice, implying that the B-repeats may have a second function, in addition to Fg-binding. These data demonstrate that two distinct M5 regions, including the HVR, are essential to virulence during the early stages of an infection. In particular, our data provide the first in vivo evidence that the HVR of an M protein plays a major role in virulence, focusing interest on the molecular role of this region.

Emerging role of the interleukin-8 cleaving enzyme SpyCEP in clinical Streptococcus pyogenes infection

Neutrophil chemoattractant interleukin (IL)-8 is cleaved and inactivated by the Streptococcus pyogenes cell envelope protease SpyCEP. A range of clinical S. pyogenes strains of differing emm type demonstrated SpyCEP activity, although transcription of the SpyCEP gene cepA differed 1000-fold between isolates. Disruption of the 2-component regulatory system covR/S in pharyngeal isolates increased cepA transcription 100-fold; this finding is consistent with endogenous CovR/S-mediated repression of cepA being responsible for low SpyCEP expression in some S. pyogenes strains associated with pharyngitis. Among patients with invasive S. pyogenes infection, disease severity and outcome were associated with the SpyCEP activity of the isolate. Lethal invasive isolate H292 (emm81) expressed more cepA than did other tested isolates. This strain carried a unique covR mutation that impaired binding to the cepA promoter. CovR/S sequence comparison in other clinical isolates revealed community-wide dissemination of covS mutations but not covR mutations. The results highlight a potential hazard and underline the importance of continuing molecular epidemiological surveillance for community-wide dissemination of CovR/S mutant hyperinvasive strains.

First Streptococcus pyogenes signature-tagged mutagenesis screen identifies novel virulence determinants

The virulence of bacterial pathogens is a complex process that requires the dynamic expression of many genes for the pathogens to invade and circumvent host defenses, as well as to proliferate in vivo. In this study, we employed a large-scale screen, signature-tagged mutagenesis (STM), to identify Streptococcus pyogenes virulence genes important for pathogenesis within the host. Approximately 1,200 STM mutants were created and screened using the zebrafish infectious disease model. The transposon insertion site was identified for 29 of the 150 mutants that were considered attenuated for virulence. Previously reported streptococcal virulence genes, such as mga, hasA, amrA, smeZ, and two genes in the sil locus, were identified, confirming the utility of the model for revealing genes important for virulence. Multiple genes not previously implicated in virulence were also identified, including genes encoding putative transporters, hypothetical cytosolic proteins, and macrolide efflux pumps. The STM mutant strains display various levels of attenuation, and multiple separate insertions were identified in either the same gene or the same locus, suggesting that these factors are important for this type of acute, invasive infection. We further examined two such genes, silB and silC of a putative quorum-sensing regulon, and determined that they are significant virulence factors in our model of necrotizing fasciitis. sil locus promoter expression was examined under various in vitro conditions, as well as in zebrafish tissues, and was found to be differentially induced. This study was a unique investigation of S. pyogenes factors required for successful invasive infection.

Muscle injury, vimentin expression, and nonsteroidal anti-inflammatory drugs predispose to cryptic group A streptococcal necrotizing infection

BACKGROUND

Myonecrosis due to group A streptococci (GAS) often develops at sites of nonpenetrating muscle injury, and nonsteroidal anti-inflammatory drugs (NSAIDs) may increase the severity of these cryptic infections. We have previously shown that GAS bind to vimentin on injured skeletal muscles in vitro. The present study investigated whether vimentin up-regulation in injured muscles in vivo is associated with homing of circulating GAS to the injured site and whether NSAIDs facilitate this process.

METHODS

M type 3 GAS were delivered intravenously 48 h after eccentric contraction (EC)-induced injury of murine hind-limb muscles. Vimentin gene expression and homing of GAS were followed by real-time reverse-transcriptase polymerase chain reaction and quantitative bacteriology of muscle homogenates, respectively. In separate experiments, ketorolac tromethamine (Toradol) was given 1 h before GAS infusion.

RESULTS

Vimentin was up-regulated approximately 8-fold 48 h after EC. Significantly more GAS were found in moderately injured muscles than in noninjured controls. NSAIDs greatly augmented the number of GAS in injured muscles.

CONCLUSIONS

Vimentin may tether circulating GAS to injured muscle, and NSAIDs enhance this process. Strategies targeting the vimentin-GAS interaction may prevent or attenuate GAS myonecrosis. Use of NSAIDs should increase suspicion of cryptic GAS infection in patients with increasing pain at sites of nonpenetrating muscle injury.

The IL-8 protease SpyCEP/ScpC of group A Streptococcus promotes resistance to neutrophil killing

Interleukin-8 (IL-8) promotes neutrophil-mediated host defense through its chemoattractant and immunostimulatory activities. The Group A Streptococcus (GAS) protease SpyCEP (also called ScpC) cleaves IL-8, and SpyCEP expression is strongly upregulated in vivo in the M1T1 GAS strains associated with life-threatening systemic disease including necrotizing fasciitis. Coupling allelic replacement with heterologous gene expression, we show that SpyCEP is necessary and sufficient for IL-8 degradation. SpyCEP decreased IL-8-dependent neutrophil endothelial transmigration and bacterial killing, the latter by reducing neutrophil extracellular trap formation. The knockout mutant lacking SpyCEP was attenuated for virulence in murine infection models, and SpyCEP expression conferred protection to coinfecting bacteria. We also show that the zoonotic pathogen Streptococcus iniae possesses a functional homolog of SpyCEP (CepI) that cleaves IL-8, promotes neutrophil resistance, and contributes to virulence. By inactivating the multifunctional host defense peptide IL-8, the SpyCEP protease impairs neutrophil clearance mechanisms, contributing to the pathogenesis of invasive streptococcal infection.

Molecular mechanisms underlying group A streptococcal pathogenesis

Group A Streptococcus (GAS) is a versatile human pathogen causing diseases ranging from uncomplicated mucosal infections to life-threatening invasive disease. The development of human-relevant animal models of GAS infection and introduction of new technologies have markedly accelerated the pace of discoveries related to GAS host-pathogen interactions. For example, recently investigators have identified pili on the GAS cell surface and learned that they are key components for adherence to eukaryotic cell surfaces. Similarly, the recent development of a transgenic mouse expressing human plasminogen has resulted in new understanding of the molecular processes contributing to invasive infection. Improved understanding of the molecular mechanisms underlying the pathogenesis of GAS pharyngeal, invasive and other infections holds the promise of assisting with the development of novel preventive or therapeutic agents for this prevalent human pathogen.

Evolution of the zebrafish model: from development to immunity and infectious disease

The successful zebrafish developmental model has now expanded to being used as a model for the analysis of host-pathogen interactions during infectious disease. Numerous pathogens have been demonstrated to infect zebrafish and new mechanisms of virulence, as well as host defense have been uncovered using this new model. In this review we summarize the literature on how the zebrafish infectious disease model is being used to decipher virulence mechanisms used by various pathogens and the host defense mechanisms initiated to combat infection.

A chemokine-degrading extracellular protease made by group A Streptococcus alters pathogenesis by enhancing evasion of the innate immune response

Circumvention of the host innate immune response is critical for bacterial pathogens to infect and cause disease. Here we demonstrate that the group A Streptococcus (GAS; Streptococcus pyogenes) protease SpyCEP (S. pyogenes cell envelope protease) cleaves granulocyte chemotactic protein 2 (GCP-2) and growth-related oncogene alpha (GROalpha), two potent chemokines made abundantly in human tonsils. Cleavage of GCP-2 and GROalpha by SpyCEP abrogated their abilities to prime neutrophils for activation, detrimentally altering the innate immune response. SpyCEP expression is negatively regulated by the signal transduction system CovR/S. Purified recombinant CovR bound the spyCEP gene promoter region in vitro, indicating direct regulation. Immunoreactive SpyCEP protein was present in the culture supernatants of covR/S mutant GAS strains but not in supernatants from wild-type strains. However, wild-type GAS strains do express SpyCEP, where it is localized to the cell wall. Strain MGAS2221, an organism representative of the highly virulent and globally disseminated M1T1 GAS clone, differed significantly from its isogenic spyCEP mutant derivative strain in a mouse soft tissue infection model. Interestingly, and in contrast to previous studies, the isogenic mutant strain generated lesions of larger size than those formed following infection with the parent strain. The data indicate that SpyCEP contributes to GAS virulence in a strain- and disease-dependent manner.

A non-human primate model of acute group a Streptococcus pharyngitis

This chapter describes methods for using non-human primates as a model of group A streptococcal (GAS) pharyngitis. This model has been used successfully to study host-pathogen interactions occurring during pharyngeal GAS infections. The protocol as described will compare two different GAS strains for their ability to cause clinical symptoms of pharyngitis.

SalY of the Streptococcus pyogenes lantibiotic locus is required for full virulence and intracellular survival in macrophages

Streptococcus pyogenes utilizes numerous mechanisms for evading the host immune response but has only recently been found to survive in the intracellular environment. In this study, we demonstrate the requirement of a putative ABC transporter permease for intracellular survival in macrophages. The highly attenuated S. pyogenes mutant, SalY, was identified from a transposon mutagenesis screen, with over 200-fold attenuation in virulence in a zebrafish invasive-disease model. Sequencing of the region surrounding the insertion identified a locus that is highly conserved in other S. pyogenes genomes and is homologous to an operon involved in lantibiotic production. In vitro analysis demonstrated that the SalY mutant is deficient in intracellular survival in murine macrophages, a phenotype also observed in zebrafish macrophages in vivo. Macrophage crude cell lysates added to bacterial cultures resulted in the death of the SalY mutant but only growth inhibition of the wild-type strain. Specific depletion of zebrafish macrophages in vivo restored the ability of the SalY mutant to cause disease to wild-type levels. The SalY-infected, macrophage-depleted zebrafish exhibit large lesions and invasive dissemination at a rate and level similar to those of the wild type. In contrast, an M protein mutant with a degree of attenuation similar to that of the SalY mutant did not regain full virulence by in vivo depletion of macrophages. The putative SalY ABC transporter may be an example of the ability of S. pyogenes to adapt and evolve new survival strategies that allow dissemination and growth in previously uninhabitable sites.

A streptococcal protease that degrades CXC chemokines and impairs bacterial clearance from infected tissues

Group A Streptococcus (GAS) causes the life-threatening infection in humans known as necrotizing fasciitis (NF). Infected subcutaneous tissues from an NF patient and mice challenged with the same GAS strain possessed high bacterial loads but a striking paucity of infiltrating polymorphonuclear leukocytes (PMNs). Impaired PMN recruitment was attributed to degradation of the chemokine IL-8 by a GAS serine peptidase. Here, we use bioinformatics approach coupled with target mutagenesis to identify this peptidase as ScpC. We show that SilCR pheromone downregulates scpC transcription via the two-component system-SilA/B. In addition, we demonstrate that in vitro, ScpC degrades the CXC chemokines: IL-8 (human), KC, and MIP-2 (both murine). Furthermore, using a murine model of human NF, we demonstrate that ScpC, but not the C5a peptidase ScpA, is an essential virulence factor. An ScpC-deficient mutant is innocuous for untreated mice but lethal for PMN-depleted mice. ScpC degrades KC and MIP-2 locally in the infected skin tissues, inhibiting PMN recruitment. In conclusion, ScpC represents a novel GAS virulence factor functioning to directly inactivate a key element of the host innate immune response.

Streptococcus pyogenes induces epithelial inflammatory responses through NF-kappaB/MAPK signaling pathways

Innate immunity involves a cascade of inflammatory events, resulting in the secretion of chemokines and cytokines to recruit mediator cells in adaptive immunity. To study epithelial inflammatory responses initiated by Streptococcus pyogenes infection, we investigated chemotaxis ability in the supernatant of infected human respiratory epithelial HEp-2 cells. Our results showed that these supernatants showed significantly increased ability to attract monocytes, implying the release of inflammatory chemoattractants into the medium. Expression of interleukin (IL)-8 and IL-6 in HEp-2 cells was significantly increased at both the mRNA and protein levels after infection with S. pyogenes. Electrophoretic mobility shift and reporter-gene assays demonstrated that the transcription factors NF-kappaB and AP-1, regulated by mitogen-activated protein (MAP) kinase, were activated after streptococcal infection. The increases in mRNAs for IL-8 and IL-6 were abrogated by addition of NF-kappaB and MAP kinase inhibitors, suggesting that the upregulation of IL-8 and IL-6 is mediated through NF-kappaB and MAP kinase signaling pathways. Taken together, our results indicate that S. pyogenes infection of epithelial cells induces the secretion of pro-inflammatory chemokines/cytokines through activation of NF-kappaB and MAP kinase signaling pathways. These early innate responses initiated by S. pyogenes-infected respiratory epithelial cells may recruit immune cells to the airway and induce inflammation.

Patterns of virulence gene expression differ between biofilm and tissue communities of Streptococcus pyogenes

The ability of Streptococcus pyogenes to form biofilm-like bacterial communities during infection of soft tissue has suggested that the capacity to produce biofilm may be important for pathogenesis. To examine this relationship, a panel of mutants was evaluated for their ability to form biofilm on abiotic surfaces in several assays. Several established virulence factors were crucial for biofilm formation, including the M protein, required for initial cell-surface interactions, and the hyaluronic acid capsule, required for subsequent maturation into a three-dimensional structure. Mutants lacking the transcription regulators Mga and CovR (CsrR) also failed to form biofilm. Comparison of transcriptional profiles revealed differential regulation of approximately 25% of the genome upon adaptation to biofilm. During infection of zebrafish, several virulence factors (notably cysteine protease and streptokinase) were regulated in a biofilm-like manner. However, the overall profile of virulence factor expression indicated that tissue communities have a pattern of gene expression different from biofilm. Taken together, these data show that while biofilm and tissue communities have many characteristics in common, that biofilm reproduces only a subset of the myriad cues used by tissue communities for regulation of virulence.

Variations in the protective immune response against streptococcal superantigens in populations of different ethnicity

Superantigens (SAgs) from group A streptococcus (GAS) are potent T cell mitogens, and have been suggested to play a role in severe streptococcal disease. Neutralizing antibodies protect against SAg-mediated disease and their levels should therefore be inversely related to severe streptococcal infection. Neutralizing anti-SAg titers in patients with severe GAS infection and patients without disease were compared in two separate groups. The first group comprised patients with invasive GAS disease from New Zealand European, Maori, and Pacific Island descent. The second group comprised Aboriginal Australian individuals with rheumatic heart disease and/or a past history of acute rheumatic fever. Patients sera were tested for their ability to neutralize T cell mitogenicity of recombinant streptococcal SAgs as a measure of functional SAg-neutralizing antibody concentration. In both studies, no inverse correlation was observed between disease and the level of serum SAg-neutralizing activity. Notably, much higher levels of natural immunity to all streptococcal SAgs were found in New Zealand Maori, New Zealand Pacific Island, and Aboriginal Australian individuals, suggesting a high degree of natural exposure and seroconversion in these groups compared to the New Zealand European cohort. Levels of serum antibodies against SAgs could not be used to predict disease susceptibility in groups with existing high levels of SAg-neutralizing antibodies.

Correlation of histopathologic findings with clinical outcome in necrotizing fasciitis

BACKGROUND

Necrotizing fasciitis is an uncommon disease with high morbidity and mortality rates. Little is known about the role of histopathologic examination in disease prognosis.

METHODS

A retrospective study was conducted to determine what correlations, if any, exist between the histopathologic features of resected tissue in patients with necrotizing fasciitis and clinical outcome.

RESULTS

Eighty-two cases of necrotizing fasciitis that occurred between January 1990 and December 2002 were identified. Histopathologic findings were available for review in 63 cases. A novel histopathologic classification scheme, based on hematoxylin-eosin and Gram stain results, was developed. The classification scheme included 3 stages: stage I, characterized by an intense neutrophilic response and an absence of bacteria in infected tissue; stage II, characterized by the presence of a moderate-to-severe neutrophilic response and positive Gram stain results or by minimal to absent neutrophilic response with a negative Gram stain result; and stage III, characterized by the presence of few or no polymorphonuclear leukocytes and a Gram stain result positive for bacteria during histopathologic examination. Patients with stage I findings had a significantly lower risk of death than patients with stage III findings (7.1% vs. 47%; odds ratio [OR], 0.1; 95% confidence interval [CI], 0.01-0.8; P=.03). Patients with stage II findings had a significantly lower mortality rate than patients with stage III findings (14.2% vs. 47%; OR, 0.2; 95% CI, 0.04-0.9; P=.04). Due to the small number of deaths (n=11) in patients for whom histopathologic examination of resected tissue was performed, multivariate analysis was not done.

CONCLUSIONS

Results of this study suggest that histopathologic findings may correlate with clinical outcome in cases of necrotizing fasciitis. Because the histopathologic scheme is based on results of commonly available stains, it could be easily adopted for use in other institutions that could further evaluate its usefulness as a prognostic tool.

Effect of a bacterial pheromone peptide on host chemokine degradation in group A streptococcal necrotising soft-tissue infections

BACKGROUND

Necrotising soft-tissue infections due to group A streptococcus (GAS) are rare (about 0.2 cases per 100000 people). The disease progresses rapidly, causing severe necrosis and hydrolysis of soft tissues. Histopathological analysis of necrotic tissue debrided from two patients (one with necrotising fasciitis and one with myonecrosis) showed large quantities of bacteria but no infiltrating neutrophils. We aimed to investigate whether the poor neutrophil chemotaxis was linked with the ability of group A streptococcus (GAS) to degrade host chemokines.

METHODS

We did RT-PCR, ELISA, and dot-blot assays to establish whether GAS induces synthesis of interleukin 8 mRNA, but subsequently degrades the released chemokine protein. Class-specific protease inhibitors were used to characterise the protease that degraded the chemokine. We used a mouse model of human soft-tissue infections to investigate the pathogenic relevance of GAS chemokine degradation, and to test the therapeutic effect of a GAS pheromone peptide (SilCR) that downregulates activity of chemokine protease.

FINDINGS

The only isolates from the necrotic tissue were two beta-haemolytic GAS strains of an M14 serotype. A trypsin-like protease released by these strains degraded human interleukin 8 and its mouse homologue MIP2. When innoculated subcutaneously in mice, these strains produced a fatal necrotic soft-tissue infection that had reduced neutrophil recruitment to the site of injection. The M14 GAS strains have a missense mutation in the start codon of silCR, which encodes a predicted 17 aminoacid pheromone peptide, SilCR. Growth of the M14 strain in the presence of SilCR abrogated chemokine proteolysis. When SilCR was injected together with the bacteria, abundant neutrophils were recruited to the site of infection, bacteria were cleared without systemic spread, and the mice survived. The therapeutic effect of SilCR was also obtained in mice challenged with M1 and M3 GAS strains, a leading cause of invasive infections.

INTERPRETATION

The unusual reduction in neutrophils in necrotic tissue of people with GAS soft-tissue infections is partly caused by a GAS protease that degrades interleukin 8. In mice, degradation can be controlled by administration of SilCR, which downregulates GAS chemokine protease activity. This downregulation increases neutrophil migration to the site of infection, preventing bacterial spread and development of a fulminant lethal systemic infection.

Contribution of glutathione peroxidase to the virulence of Streptococcus pyogenes

Glutathione peroxidases are widespread among eukaryotic organisms and function as a major defense against hydrogen peroxide and organic peroxides. However, glutathione peroxidases are not well studied among prokaryotic organisms and have not previously been shown to promote bacterial virulence. Recently, a gene with homology to glutathione peroxidase was shown to contribute to the antioxidant defenses of Streptococcus pyogenes (group A streptococcus). Since this bacterium causes numerous suppurative diseases that require it to thrive in highly inflamed tissue, it was of interest to determine if glutathione peroxidase is important for virulence. In this study, we report that GpoA glutathione peroxidase is the major glutathione peroxidase in S. pyogenes and is essential for S. pyogenes pathogenesis in several murine models that mimic different aspects of streptococcal suppurative disease. In contrast, glutathione peroxidase is not essential for virulence in a zebrafish model of streptococcal myositis, a disease characterized by the absence of an inflammatory cell infiltrate. Taken together, these data suggest that S. pyogenes requires glutathione peroxidase to adapt to oxidative stress that accompanies an inflammatory response, and the data provide the first demonstration of a role for glutathione peroxidase in bacterial virulence. The fact that genes encoding putative glutathione peroxidases are found in the genomes of many pathogenic bacterial species suggests that glutathione peroxidase may have a general role in bacterial pathogenesis.

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.

M type 1 and 3 group A streptococci stimulate tissue factor-mediated procoagulant activity in human monocytes and endothelial cells

Streptococcal toxic shock syndrome (StrepTSS) is an invasive infection characterized by marked coagulopathy, multiple organ failure, and rapid tissue destruction and is strongly associated with M type 1 and 3 group A streptococci (GAS). Initiation of the coagulation cascade with formation of microvascular thrombi contributes to multiple organ failure in human cases of gram-negative bacteremia; however, little is known regarding the mechanism of coagulopathy in StrepTSS. Thus, we investigated the abilities of several strains of M type 1 and 3 GAS isolated from human cases of StrepTSS to stimulate production of tissue factor (TF), the principal initiator of coagulation in vivo. Washed, killed M type 1 and 3 GAS, but not M type 6 GAS, elicited high-level TF-mediated procoagulant activity from both isolated human monocytes and cultured human umbilical vein endothelial cells. M type 1 GAS consistently elicited higher levels of TF from monocytes than did M type 3 GAS. GAS-induced TF synthesis in monocytes did not correlate with production of tumor necrosis factor alpha or interleukin-8. Conversely, M type 3 GAS were consistently more potent than M type 1 GAS in stimulating endothelial cell TF synthesis. These results demonstrate that (i) M type 1 and 3 strains of GAS are potent inducers of TF synthesis, (ii) GAS-induced TF synthesis is not simply an epiphenomenon of cytokine generation, and (iii) induction of TF in endothelial cells and monocytes may be M type specific. In total, these findings suggest that a novel interaction between GAS and host cells contributes to the observed coagulopathy in StrepTSS.

Application of a rat model of streptococcal shock to evaluate on-line hemoperfusion and removal of circulating superantigens

OBJECTIVE

To evaluate the efficacy of on-line hemoperfusion for the removal of circulating superantigens in a rat model of streptococcal shock.

DESIGN

In vitro and experimental animal studies.

SETTING

University research laboratories.

INTERVENTIONS

Chemically modified polystyrene-based composite fiber reinforced with polypropylene was formulated in discs and used to evaluate the removal of superantigenic toxins from culture supernatants in vitro, and from blood in vivo.

MEASUREMENTS AND MAIN RESULTS

Incubation of streptococcal supernatant with a single disc reduced the concentration of the superantigen streptococcal pyrogenic exotoxin A from 90.9 +/- 12.7 ng/mL with the control fiber to 32.5 +/- 3.6 ng/mL with active fiber (p <.001). The active discs also brought about a dose-dependent reduction in mitogenic activity that was highly significant (counts reduced from 82,133 +/- 2747 using three control discs to 26,307 +/- 3547 with three active discs [p <.001]). Beginning 6 hrs after infection, animals were hemoperfused for 3 hrs over columns containing control or active fiber. At the end of the treatment period, there was a significant decrease in the number of circulating bacteria in the active group (3.5 x 10(4) vs. 3.1 x 10(3) colony-forming units/mL, p<.05). However, bacterial counts subsequently increased and by 15 hrs and at all subsequent time points, the number of circulating bacteria was no different between the two groups. There was a highly significant and sustained difference in circulating streptococcal pyrogenic exotoxin A levels between the groups. Streptococcal pyrogenic exotoxin A levels at 9 hrs were 19.9 ng/mL in the controls vs. 2.1 ng/mL in the active group (p =.05). Animals perfused over active fibers had a highly significant survival advantage compared with control or nonperfused groups (p <.01).

CONCLUSIONS

Hemoperfusion and on-line removal of superantigens merits further study as a possible treatment strategy for streptococcal shock syndromes. The mechanism by which the fibers are operating requires further investigation.

Induction of platelet thrombi by bacteria and antibodies

We have characterized 2 distinct mechanisms through which infectious agents may promote platelet adhesion and thrombus formation in flowing blood, thus contributing to the progression of disease. In one case, the process initiates when the integrin alpha(IIb)beta(3) mediates platelet arrest onto immobilized bacterial constituents that have bound plasma fibrinogen. If blood contains antibodies against the bacteria, immunoglobulin (Ig) G may cluster on the same surface and activate adherent platelets through the Fc(gamma)RIIA receptor, leading to thrombus growth. As an alternative, bacteria that cannot bind fibrinogen may attach to substrates, such as immobilized plasma proteins or components of the extracellular matrix, which also support platelet adhesion. As a result of this colocalization, IgG bound to bacteria can activate neighboring platelets and induce thrombus growth regardless of their ability to initiate platelet-surface contact. Our results demonstrate that intrinsic constituents of infectious agents and host proteins play distinct but complementary roles in recruiting platelets into thrombi, possibly contributing to complications of acute and chronic infections.

Streptococcus-zebrafish model of bacterial pathogenesis

Due to its small size, rapid generation time, powerful genetic systems, and genomic resources, the zebrafish has emerged as an important model of vertebrate development and human disease. Its well-developed adaptive and innate cellular immune systems make the zebrafish an ideal model for the study of infectious diseases. With a natural and important pathogen of fish, Streptococcus iniae, we have established a streptococcus- zebrafish model of bacterial pathogenesis. Following injection into the dorsal muscle, zebrafish developed a lethal infection, with a 50% lethal dose of 10(3) CFU, and died within 2 to 3 days. The pathogenesis of infection resembled that of S. iniae in farmed fish populations and that of several important human streptococcal diseases and was characterized by an initial focal necrotic lesion that rapidly progressed to invasion of the pathogen into all major organ systems, including the brain. Zebrafish were also susceptible to infection by the human pathogen Streptococcus pyogenes. However, disease was characterized by a marked absence of inflammation, large numbers of extracellular streptococci in the dorsal muscle, and extensive myonecrosis that occurred far in advance of any systemic invasion. The genetic systems available for streptococci, including a novel method of mutagenesis which targets genes whose products are exported, were used to identify several mutants attenuated for virulence in zebrafish. This combination of a genetically amenable pathogen with a well-defined vertebrate host makes the streptococcus-zebrafish model of bacterial pathogenesis a powerful model for analysis of infectious disease.

Fatal group a streptococcal necrotizing myopathy

A 72-year-old woman on immunosuppressive therapy for renal transplantation was admitted to the hospital for diffuse, progressive weakness that developed over several weeks. Serum creatine kinase steadily increased and she developed myoglobinuria. Blood cultures were positive for group A Streptococcus pyogenes. The muscle biopsy demonstrated a necrotizing myopathy without cellular infiltrate. Despite treatment, she evolved to multiorgan system failure and cardiovascular collapse. This is a novel presentation of group A streptococcal muscle infection with diffuse, generalized muscle weakness. It stands in striking contrast to the usual infection with this organism confined to one extremity and associated with a prolific cellular response in the muscle.

Streptolysin S and necrotising infections produced by group G streptococcus

BACKGROUND

We encountered three patients with severe necrotising soft tissue infections due to beta-haemolytic group G streptococcus. Due to strong clinical similarities with invasive infections produced by group A streptococcus, we investigated a potential link of shared beta-haemolytic phenotype to disease pathogenesis.

METHODS

Hybridisation, DNA sequencing, targeted mutagenesis, and complementation studies were used to establish the genetic basis for group G streptococcus beta-haemolytic activity. The requirement of group G streptococcus beta-haemolysin in producing necrotising infection was examined in mice.

FINDINGS

Each patient had an underlying medical condition. beta-haemolytic group G streptococcus was the sole microbial isolate from debrided necrotic tissue. The group G streptococcus chromosome contained a homologue of the nine-gene group A streptococcus sag operon encoding the beta-haemolysin streptolysin S (SLS). Targeted mutagenesis of the putative SLS structural gene sagA in group G streptococcus eliminated beta-haemolytic activity. Mice injected subcutaneously with wild-type group A streptococcus or group G streptococcus developed an inflammatory lesion with high bacterial counts, marked neutrophil infiltration, and histopathological evidence of diffuse tissue necrosis. These changes were not found in mice injected with the isogenic group A streptococcus or group G streptococcus SLS-negative mutants.

INTERPRETATION

In patients with underlying medical conditions, beta-haemolytic group G streptococcus can produce necrotising soft tissue infections resembling those produced by group A streptococcus. The beta-haemolytic phenotype of group G streptococcus is produced by the exotoxin SLS, encoded by a functional homologue of the nine-gene group A streptococcus sag operon. SLS expression contributes to the pathogenesis of streptococcal necrotising soft tissue infection.

Necrotizing fasciitis due to penicillin-resistant Streptococcus pneumoniae: case report and review of the literature

Necrotizing fasciitis (NF) is a life-threatening infection involving rapid necrosis of subcutaneous and fascial tissues. Streptococcus pneumoniae (SPN) soft tissue infection is exceedingly uncommon, reported primarily in patients with immunosuppression or other underlying conditions. We report a case of NF and septic shock in a healthy 32-year-old man, whose only predisposing factor was antecedent blunt trauma. Pathological examination and culture of the extensive tissue debridement were positive only for SPN. The serotype 9V isolate was penicillin (PCN)-resistant (MIC=2.0), and closely-related by pulse field gel electrophoresis and multilocus fingerprinting to clone France 9V-3, an important genetic reservoir for increasing PCN-resistance worldwide. This unique case has implications for our pathogenic under-standing and empiric management of NF.