Group A Streptococcal Infections Research Articles

Highly virulent M1 Streptococcus pyogenes isolates resistant to clindamycin

ContextEmm1-type group A Streptococcus (GAS), or Streptococcus pyogenes, is mostly responsible for invasive infections such as necrotizing fasciitis (NF) and streptococcal toxic shock syndrome (STSS). The recommended treatment of severe invasive GAS infections is a combination of clindamycin and penicillin. Until 2012, almost all emm1 isolates were susceptible to clindamycin. ObjectivesWe aimed to identify the phenotypic and genotypic characteristics of emm1 GAS clone resistant to clindamycin. MethodsGAS strains were characterized by emm sequence typing, detection of genes encoding pyrogenic exotoxins or superantigens. Cluster analysis was performed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Antibiotic susceptibility was assessed using disk diffusion and resistance genes were detected by PCR. ResultsA total of 1321 GAS invasive isolates were analyzed between January 2011 and December 2012. The overall number of invasive isolates resistant to clindamycin was 52 (3.9%); seven of them were emm1 isolates. All isolates had the same genomic markers: macrolide resistance due to the presence of the erm(B) gene, emm subtype 1.0, the same toxin or superantigen profile, PFGE pattern and sequence type. ConclusionThis is the first description of highly virulent GAS emm1 isolates resistant to clindamycin in France. This article strengthens the need for monitoring the epidemiology of invasive GAS strains as they could lead to changes in treatment guidelines.

High Incidence of Invasive Group A Streptococcus Disease Caused by Strains of Uncommon emm Types in Thunder Bay, Ontario, Canada.

An outbreak of type emm59 invasive group A Streptococcus (iGAS) disease was declared in 2008 in Thunder Bay District, Northwestern Ontario, 2 years after a countrywide emm59 epidemic was recognized in Canada. Despite a declining number of emm59 infections since 2010, numerous cases of iGAS disease continue to be reported in the area. We collected clinical information on all iGAS cases recorded in Thunder Bay District from 2008 to 2013. We also emm typed and sequenced the genomes of all available strains isolated from 2011 to 2013 from iGAS infections and from severe cases of soft tissue infections. We used whole-genome sequencing data to investigate the population structure of GAS strains of the most frequently isolated emm types. We report an increased incidence of iGAS in Thunder Bay compared to the metropolitan area of Toronto/Peel and the province of Ontario. Illicit drug use, alcohol abuse, homelessness, and hepatitis C infection were underlying diseases or conditions that might have predisposed patients to iGAS disease. Most cases were caused by clonal strains of skin or generalist emm types (i.e., emm82, emm87, emm101, emm4, emm83, and emm114) uncommonly seen in other areas of the province. We observed rapid waxing and waning of emm types causing disease and their replacement by other emm types associated with the same tissue tropisms. Thus, iGAS disease in Thunder Bay District predominantly affects a select population of disadvantaged persons and is caused by clonally related strains of a few skin and generalist emm types less commonly associated with iGAS in other areas of Ontario.

The Mga Regulon but Not Deoxyribonuclease Sda1 of Invasive M1T1 Group A Streptococcus Contributes to In Vivo Selection of CovRS Mutations and Resistance to Innate Immune Killing Mechanisms.

Invasive M1T1 group A Streptococcus (GAS) can have a mutation in the regulatory system CovRS, and this mutation can render strains hypervirulent. Interestingly, via mechanisms that are not well understood, the host innate immune system's neutrophils select spontaneous M1T1 GAS CovRS hypervirulent mutants, thereby enhancing the pathogen's ability to evade immune killing. It has been reported that the DNase Sda1 is critical for the resistance of M1T1 strain 5448 to killing in human blood and provides pressure for in vivo selection of CovRS mutations. We reexamined the role of Sda1 in the selection of CovRS mutations and in GAS innate immune evasion. Deletion of sda1 or all DNase genes in M1T1 strain MGAS2221 did not alter emergence of CovRS mutants during murine infection. Deletion of sda1 in strain 5448 resulted in Δsda1 mutants with (5448 Δsda1(M+) strain) and without (5448 Δsda1(M-) strain) M protein production. The 5448 Δsda1(M+) strain accumulated CovRS mutations in vivo and resisted killing in the bloodstream, whereas the 5448 Δsda1(M-) strain lost in vivo selection of CovRS mutations and was sensitive to killing. The deletion of emm and a spontaneous Mga mutation in MGAS2221 reduced and prevented in vivo selection for CovRS mutants, respectively. Thus, in contrast to previous reports, Sda1 is not critical for in vivo selection of invasive M1T1 CovRS mutants and GAS resistance to innate immune killing mechanisms. In contrast, M protein and other Mga-regulated proteins contribute to the in vivo selection of M1T1 GAS CovRS mutants. These findings advance the understanding of the progression of invasive M1T1 GAS infections.

Adaptive Immunity against Streptococcus pyogenes in Adults Involves Increased IFN-γ and IgG3 Responses Compared with Children.

Each year, millions of people are infected with Streptococcus pyogenes, leading to an estimated 500,000 annual deaths worldwide. For unknown reasons, school-aged children have substantially higher infection rates than adults. The goal for this study was to provide, to our knowledge, the first detailed characterization of the human adaptive immune response against S. pyogenes in both children and adults. We report that all adults in our study, as well as most children, showed immunity against the two conserved group A streptococci (GAS) Ags, streptococcal C5a peptidase and immunogenic secreted protein. The response primarily consisted of three subsets of Th1 T cells, in which the TNF-α(+) and IL-2(+)TNF-α(+) subsets were most frequent. Humoral immunity was dominated by IgG1 and IgG3, whereas the Th2-associated IgG4 isotype was only detected at very low amounts. IgG3 levels correlated significantly with IFN-γ, but not with IL-5, IL-13, IL-17, or TNF-α. Interestingly, children showed a similar pattern of Ag-specific cytokine release, but displayed significantly lower levels of IgG3 and IFN-γ compared with adults. Thus, human immune responses against S. pyogenes consist of a robust Th1 cellular memory response in combination with IgG1/IgG3-dominated humoral immunity that increase with age. The significance of these data regarding both the increased GAS infection rate in children and the development of protective GAS vaccines is discussed.

Prevalence of group A streptococcal disease in North and Sub-Saharan Africa: a systematic review protocol

IntroductionThe true burden of group A streptococcal (GAS) disease in Africa is not known. GAS is a significant cause of mortality and morbidity on the global scale and in developing...

Virulence of Group A Streptococci Is Enhanced by Human Complement Inhibitors

Streptococcus pyogenes, also known as Group A Streptococcus (GAS), is an important human bacterial pathogen that can cause invasive infections. Once it colonizes its exclusively human host, GAS needs to surmount numerous innate immune defense mechanisms, including opsonization by complement and consequent phagocytosis. Several strains of GAS bind to human-specific complement inhibitors, C4b-binding protein (C4BP) and/or Factor H (FH), to curtail complement C3 (a critical opsonin) deposition. This results in diminished activation of phagocytes and clearance of GAS that may lead to the host being unable to limit the infection. Herein we describe the course of GAS infection in three human complement inhibitor transgenic (tg) mouse models that examined each inhibitor (human C4BP or FH) alone, or the two inhibitors together (C4BPxFH or ‘double’ tg). GAS infection with strains that bound C4BP and FH resulted in enhanced mortality in each of the three transgenic mouse models compared to infection in wild type mice. In addition, GAS manifested increased virulence in C4BPxFH mice: higher organism burdens and greater elevations of pro-inflammatory cytokines and they died earlier than single transgenic or wt controls. The effects of hu-C4BP and hu-FH were specific for GAS strains that bound these inhibitors because strains that did not bind the inhibitors showed reduced virulence in the ‘double’ tg mice compared to strains that did bind; mortality was also similar in wild-type and C4BPxFH mice infected by non-binding GAS. Our findings emphasize the importance of binding of complement inhibitors to GAS that results in impaired opsonization and phagocytic killing, which translates to enhanced virulence in a humanized whole animal model. This novel hu-C4BPxFH tg model may prove invaluable in studies of GAS pathogenesis and for developing vaccines and therapeutics that rely on human complement activation for efficacy.

Public health management of group A streptococcal infection in mother-baby pairs in England; a case series review

Group A streptococci (GAS) are causative organisms in a large and increasing proportion of UK puerperal sepsis deaths, and remain an important consideration in neonatal sepsis in the UK and around the world. UK guidelines advise that both mother and baby should be treated with antibiotics if either develops an invasive GAS (iGAS) infection in the 28 days following birth to reduce the risk of iGAS developing in the other party.

Serotype M3 and M28 Group A Streptococci Have Distinct Capacities to Evade Neutrophil and TNF-α Responses and to Invade Soft Tissues.

The M3 Serotype of Group A Streptococcus (GAS) is one of the three most frequent serotypes associated with severe invasive GAS infections, such as necrotizing fasciitis, in the United States and other industrialized countries. The basis for this association and hypervirulence of invasive serotype M3 GAS is not fully understood. In this study, the sequenced serotype M3 strain, MGAS315, and serotype M28 strain, MGAS6180, were characterized in parallel to determine whether contemporary M3 GAS has a higher capacity to invade soft tissues than M28 GAS. In subcutaneous infection, MGAS315 invaded almost the whole skin, inhibited neutrophil recruitment and TNF-α production, and was lethal in subcutaneous infection of mice, whereas MGAS6180 did not invade skin, induced robust neutrophil infiltration and TNF-α production, and failed to kill mice. In contrast to MGAS6180, MGAS315 had covS G1370T mutation. Either replacement of the covS 1370T gene with wild-type covS in MGAS315 chromosome or in trans expression of wild-type covS in MGAS315 reduced expression of CovRS-controlled virulence genes hasA, spyCEP, and sse by >10 fold. MGAS315 covS wt lost the capacity to extensively invade skin and to inhibit neutrophil recruitment and had attenuated virulence, indicating that the covS G1370T mutation critically contribute to the hypervirulence of MGAS315. Under the background of functional CovRS, MGAS315 covS wt still caused greater lesions than MGAS6180, and, consistently under the background of covS deletion, MGAS6180 ΔcovS caused smaller lesions than MGAS315 ΔcovS. Thus, contemporary invasive M3 GAS has a higher capacity to evade neutrophil and TNF-α responses and to invade soft tissue than M28 GAS and that this skin-invading capacity of M3 GAS is maximized by natural CovRS mutations. These findings enhance our understanding of the basis for the frequent association of M3 GAS with necrotizing fasciitis.

The roles of injury and nonsteroidal anti-inflammatory drugs in the development and outcomes of severe group A streptococcal soft tissue infections.

This review summarizes clinical and basic science evidence linking trauma and nonsteroidal anti-inflammatory drug (NSAID) use to initiation and progression of severe group A streptococcal (GAS) soft tissue infection. New evidence includes recent clinical series and controlled studies that lend support to an NSAID/GAS association, basic science studies that demonstrate unique roles for nonpenetrating injury and NSAID administration in initiation of cryptogenic GAS infection and experimental studies showing that nonselective NSAIDs accelerate disease progression and limit antibiotic efficacy in established GAS soft tissue infections. Potential mechanisms for these processes are discussed. NSAIDs are important anti-inflammatory and analgesic drugs; however, new experimental data suggest that nonselective NSAIDs do more than simply mask the signs and symptoms of developing GAS infection. A more thorough understanding of the triadic interplay of injury-triggered immune signaling, GAS soft tissue infection and NSAIDs is of significant clinical importance and could shift the current paradigm of pain management to avert the consequences of such devastating infections.

Molecular characterization of macrolide resistant Streptococcus pyogenes isolates from pharyngitis patients in Serbia

A steady increase in macrolide resistance in Streptococcus pyogenes, group A streptococci (GAS) was reported in Serbia during 2004–2009 (9.9%). However, there are no data on the molecular epidemiology of pharyngeal macrolide resistance GAS (MRGAS) isolates. Therefore, the aims of this first nationwide study were to examine the prevalence of macrolide resistance in Serbian GAS and to determine their resistance phenotypes, genotypes and clonal relationships. Overall 3893 non-duplicate pharyngeal S. pyogenes isolates from outpatients with GAS infection were collected throughout country during 2008 and 2009. Among 486 macrolide resistant pharyngeal isolates collected, 103 were further characterized. Macrolide resistance phenotypes and genotypes were determined by double-disk diffusion test and PCR, respectively. Strain relatedness was determined by emm typing, multilocus sequence typing (MLST), multilocus variable tandem repeat analysis (MLVA), phage profiling (PP) and virulence factor profiling (VFP). Overall, macrolide resistance among GAS isolates in Serbia was 12.5%. M phenotype was the most common (71.8%), followed by iMLS (18.4%) and cMLS (9.7%). Three clonal complexes – emm75/mefA/ST49, emm12/mefA/ST36 and emm77/ermA/tetO/ST63 comprised over 90% of the tested strains. Although MLVA, PP and VFP distinguished 10, 20 and 12 different patterns, respectively, cluster analysis disclosed only small differences between strains which belonged to the same emm/ST type. Our data indicate dominance of three major internationally widely disseminated macrolide resistant clones and a high genetic homogeneity among the Serbian MRGAS population. Continued surveillance of macrolide resistance and clonal composition in MRGAS in Serbia in future is necessary to determine stability of MRGAS clones and to guide therapy strategies.

Streptococcal pharyngitis in schoolchildren in Bamako, Mali.

Group A streptococcus (GAS) pharyngitis is associated with high rates of rheumatic heart disease in developing countries. We sought to identify guidelines for empiric treatment of pharyngitis in low-resource settings. To inform the design of GAS vaccines, we determined the emm types associated with pharyngitis among African schoolchildren. Surveillance for pharyngitis was conducted among children 5-16 years of age attending schools in Bamako, Mali. Students were encouraged to visit a study clinician when they had a sore throat. Enrollees underwent evaluation and throat swab for isolation of GAS. Strains were emm typed by standard methods. GAS was isolated from 449 (25.5%) of the 1,759 sore throat episodes. Painful cervical adenopathy was identified in 403 children (89.8%) with GAS infection and was absent in 369 uninfected children (28.2%). Emm type was determined in 396 (88.2%) of the 449 culture-positive children; 70 types were represented and 14 types accounted for 49% of isolates. Based on the proportion of the 449 isolates bearing emm types included in the 30-valent vaccine (31.0%) plus nonvaccine types previously shown to react to vaccine-induced bactericidal antibodies (44.1%), the vaccine could protect against almost 75% of GAS infections among Bamako schoolchildren. Two promising strategies could reduce rheumatic heart disease in low-resource settings. Administering antibiotics to children with sore throat and tender cervical adenopathy could treat most GAS-positive children while reducing use of unnecessary antibiotics for uninfected children. Broad coverage against M types associated with pharyngitis in Bamako schoolchildren might be achieved with the 30-valent GAS vaccine under development.

A Neutralizing Monoclonal IgG1 Antibody of Platelet-Activating Factor Acetylhydrolase SsE Protects Mice against Lethal Subcutaneous Group A Streptococcus Infection.

Group A Streptococcus (GAS) can cause life-threatening invasive infections, including necrotizing fasciitis. There are no effective treatments for severe invasive GAS infections. The platelet-activating factor (PAF) acetylhydrolase SsE produced by GAS is required for invasive GAS to evade innate immune responses and to invade soft tissues. This study determined whether the enzymatic activity of SsE is critical for its function in GAS skin invasion and inhibition of neutrophil recruitment and whether SsE is a viable target for immunotherapy for severe invasive GAS infections. An isogenic derivative of M1T1 strain MGAS5005 producing SsE with an S178A substitution (SsE(S178A)), an enzymatically inactive SsE mutant protein, was generated. This strain induced higher levels of neutrophil infiltration and caused smaller lesions than MGAS5005 in subcutaneous infections of mice. This phenotype is similar to that of MGAS5005 sse deletion mutants, indicating that the enzymatic activity of SsE is critical for its function. An anti-SsE IgG1 monoclonal antibody (MAb), 2B11, neutralized the PAF acetylhydrolase activity of SsE. Passive immunization with 2B11 increased neutrophil infiltration, reduced skin invasion, and protected mice against MGAS5005 infection. However, 2B11 did not protect mice when it was administered after MGAS5005 inoculation. MGAS5005 induced vascular effusion at infection sites at early hours after GAS inoculation, suggesting that 2B11 did not always have access to infection sites. Thus, the enzymatic activity of SsE mediates its function, and SsE has the potential to be included in a vaccine but is not a therapeutic target. An effective MAb-based immunotherapy for severe invasive GAS infections may need to target virulence factors that are critical for systemic survival of GAS.

The Mysteries of Streptococcal Pharyngitis.

Streptococcal pharyngitis is common in children between 5 and 15 years of age. While there is a “classic” presentation, few patients have all of the characteristic signs and symptoms. Therefore, for those children who present with a sore throat in the absence of other respiratory symptoms such as nasal congestion and cough, the best method of determining the etiology of the illness is to obtain a swab of the tonsils and posterior pharynx and to test it for the presence of Group A Streptococci (GAS). Performing this testing, allows the clinician to safely avoid the use of antibiotics in children who do not test positive for this pathogen. These children are more likely to have a viral cause for their illness. Conversely, those who test positive for GAS can be offered antibiotics, such as penicillin or amoxicillin for treatment. Administering antimicrobial therapy will lead to more rapid clinical improvement and will decrease person to person transmission. In addition, it will prevent suppurative and some non-suppurative complications such as rheumatic fever. Some patients will have multiple episodes of illness during one school year associated with a positive test for GAS. This either represents true recurrent GAS infections or recurrent viral illnesses in children who have become streptococcal carriers. There are strategies to assist with the clinical management of both of these groups of children.

M1 Protein from GAS Protects against Histone Killing

Histones are an essential element of chromatin structure and necessary for eukaryotic survival. Highly positively charged, histones resemble small, cationicantimicrobial peptides (AMPs) of the mammalian innate immune system. The broad‐spectrum bactericidal action of histones against a variety of bacteria was first described in 1958. More recently, a framework for histone function in host defense in vivo was revealed with the discovery of neutrophil extracellular traps (NETs), DNA and histone‐based structures extruded by neutrophils to entrap and kill bacteria. Here, we explore histone resistance of several Gram‐positive bacterial pathogens and observe that one important human pathogen, group A Streptococcus (GAS), is highly resistant to histone killing. A screen of isogenic GAS mutants lacking various virulence factor genes revealed that the surface‐anchored M1 protein is associated with high‐level histone resistance. Studies utilizing purified protein and heterologous gene expression showed M1 to be both necessary and sufficient to confer histone resistance. The capacity of M1 to sequester histones and promote accumulatation of host fibrinogen as a further steric hindrance factor, blocked histone access to the bacterial cell wall. M1‐mediated histone resistance was correlated with enhanced GAS survival in NETs. This is the first description of a Gram‐positive bacterial resistance mechanism to histone killing, which in turn contributes to NET resistance. Histone resistance is likely a contributing factor to the well‐established virulence role of M1 in invasive GAS infection.This research was supported by NIH grant (AI096837) to PG and VN.

Clinical presentation of pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections in research and community settings.

The first cases of pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS) were described >15 years ago. Since that time, the literature has been divided between studies that successfully demonstrate an etiologic relationship between Group A streptococcal (GAS) infections and childhood-onset obsessive-compulsive disorder (OCD), and those that fail to find an association. One possible explanation for the conflicting reports is that the diagnostic criteria proposed for PANDAS are not specific enough to describe a unique and homogeneous cohort of patients. To evaluate the validity of the PANDAS criteria, we compared clinical characteristics of PANDAS patients identified in two community practices with a sample of children meeting full research criteria for PANDAS. A systematic review of clinical records was used to identify the presence or absence of selected symptoms in children evaluated for PANDAS by physicians in Hinsdale, Illinois (n=52) and Bethesda, Maryland (n=40). RESULTS were compared against data from participants in National Institute of Mental Health (NIMH) research investigations of PANDAS (n=48). As described in the original PANDAS cohort, males outnumbered females (95:45) by ∼ 2:1, and symptoms began in early childhood (7.3±2.7 years). Clinical presentations were remarkably similar across sites, with all children reporting acute onset of OCD symptoms and multiple comorbidities, including separation anxiety (86-92%), school issues (75-81%), sleep disruptions (71%), tics (60-65%), urinary symptoms (42-81%), and others. Twenty of the community cases (22%) failed to meet PANDAS criteria because of an absence of documentation of GAS infections. The diagnostic criteria for PANDAS can be used by clinicians to accurately identify patients with common clinical features and shared etiology of symptoms. Although difficulties in documenting an association between GAS infection and symptom onset/exacerbations may preclude a diagnosis of PANDAS in some children with acute-onset OCD, they do appear to meet criteria for pediatric acute-onset neuropsychiatric syndrome (PANS).

Multidisciplinary clinic dedicated to treating youth with pediatric acute-onset neuropsychiatric syndrome: presenting characteristics of the first 47 consecutive patients.

Abrupt, dramatic onset obsessive-compulsive disorder (OCD) and/or eating restriction with at least two coinciding symptoms (anxiety, mood dysregulation, irritability/aggression/oppositionality, behavioral regression, cognitive deterioration, sensory or motor abnormalities, or somatic symptoms) defines pediatric acute-onset neuropsychiatric syndrome (PANS). Descriptions of clinical data in such youth are limited. We reviewed charts of 53 consecutive patients evaluated in our PANS Clinic; 47 met PANS symptom criteria but not all met the requirement for "acute onset." Patients meeting full criteria for PANS were compared with patients who had a subacute/insidious onset of symptoms. Nineteen of 47 (40%) patients in the study had acute onset of symptoms. In these patients, autoimmune/inflammatory diseases and psychiatric disorders were common in first-degree family members (71% and 78%, respectively). Most acute-onset patients had a relapsing/remitting course (84%), prominent sleep disturbances (84%), urinary issues (58%), sensory amplification (66%), gastrointestinal symptoms (42%), and generalized pain (68%). Inflammatory back pain (21%) and other arthritis conditions (28%) were also common. Suicidal and homicidal thoughts and gestures were common (44% and 17%, respectively) as were violent outbursts (61%). Group A streptococcus (GAS) was the most commonly identified infection at onset (21%) and during flares (74%). Rates of the above-mentioned characteristics did not differ between the acute-onset group and the subacute/insidious-onset groups. Low levels of immunoglobulins were more common in the subacute/insidious-onset group (75%) compared with the acute-onset group (22%), but this was not statistically significant (p=0.06). In our PANS clinic, 40% of patients had acute onset of symptoms. However, those with and without acute onset of symptoms had similar symptom presentation, rates of inflammatory conditions, somatic symptoms, and violent thoughts and behaviors. GAS infections were the most commonly identified infection at onset and at symptom flares. Because of the wide variety of medical and psychiatric symptoms, youth with PANS may require a multidisciplinary team for adequate care management.

Application of the C3-binding motif of streptococcal pyrogenic exotoxin B to protect mice from invasive group a streptococcal infection.

Group A streptococcus (GAS) is an important human pathogen that produces several extracellular exotoxins to facilitate invasion and infection. Streptococcal pyrogenic exotoxin B (SPE B) has been demonstrated to be an important virulence factor of GAS. Our previous studies indicate that SPE B cleaves complement 3 (C3) and inhibits the activation of complement pathways. In this study, we constructed and expressed recombinant fragments of SPE B to examine the C3-binding site of SPE B. Using enzyme-linked immunosorbent assays and pull-down assays, we found that the C-terminal domain, containing amino-acid residues 345–398, of SPE B was the major binding site of human serum C3. We further identified a major, Ala376-Pro398, and a minor C3-binding motif, Gly346-Gly360, that both mediated the binding of C3 complement. Immunization with the C3-binding motifs protected mice against challenge with a lethal dose of non-invasive M49 strain GAS but not invasive M1 strains. To achieve higher efficiency against invasive M1 GAS infection, a combination of synthetic peptides derived from C-terminal epitope of streptolysin S (SLSpp) and from the major C3-binding motif of SPE B (PP6, Ala376-Pro398) was used to elicit specific immune response to those two important streptococcal exotoxins. Death rates and the severity of skin lesions decreased significantly in PP6/SLSpp-immunized mice that were infected with invasive M1 strains of GAS. These results indicate a combination of the C3-binding motif of SPE B and the protective epitope of SLS could be used as a subunit vaccine against invasive M1 strains group A streptococcal infection.

Distribution of emm types among group A Streptococcus isolates from children in Korea

We analyzed 155 clinical group A Streptococcus (GAS) isolates from children at the Seoul National University Children's Hospital between 1991 and 2012 and the Seoul National University Bundang Hospital between 2006 and 2012. The erythromycin resistance rate was 10.3% (16/155), and all isolates during the recent 3years were susceptible to erythromycin. Among isolates, emm1 (19.4%), emm12 (18.7%), and emm4 (18.1%) were the most prevalent emm types. According to clinical disease, emm1 was most common in invasive GAS infections (47.4%), and emm4, in scarlet fever (48.8%). From 2010 to 2012, an increase in invasive GAS infections and scarlet fever that correlated with an increase in emm1 and emm4 types was observed. The speC detection rate was higher in patients with scarlet fever than in those with other GAS infections (P=0.017). Recently, invasive GAS infections and scarlet fever were associated with an increase in emm1 and emm4, respectively.

Characterization of the Effect of the Histidine Kinase CovS on Response Regulator Phosphorylation in Group A Streptococcus

Two-component gene regulatory systems (TCSs) are a major mechanism by which bacteria respond to environmental stimuli and thus are critical to infectivity. For example, the control of virulence regulator/sensor kinase (CovRS) TCS is central to the virulence of the major human pathogen group A Streptococcus (GAS). Here, we used a combination of quantitative in vivo phosphorylation assays, isoallelic strains that varied by only a single amino acid in CovS, and transcriptome analyses to characterize the impact of CovS on CovR phosphorylation and GAS global gene expression. We discovered that CovS primarily serves to phosphorylate CovR, thereby resulting in the repression of virulence factor-encoding genes. However, a GAS strain selectively deficient in CovS phosphatase activity had a distinct transcriptome relative to that of its parental strain, indicating that both CovS kinase and phosphatase activities influence the CovR phosphorylation status. Surprisingly, compared to a serotype M3 strain, serotype M1 GAS strains had high levels of phosphorylated CovR, low transcript levels of CovR-repressed genes, and strikingly different responses to environmental cues. Moreover, the inactivation of CovS in the serotype M1 background resulted in a greater decrease in phosphorylated CovR levels and a greater increase in the transcript levels of CovR-repressed genes than did CovS inactivation in a serotype M3 strain. These data clarify the influence of CovS on the CovR phosphorylation status and provide insight into why serotype M1 GAS strains have high rates of spontaneous mutations in covS during invasive GAS infection, thus providing a link between TCS molecular function and the epidemiology of deadly bacterial infections.

Group A Streptococcus Modulates Host Inflammation by Manipulating Polymorphonuclear Leukocyte Cell Death Responses

Polymorphonuclear leukocyte (PMN) cell death strongly influences the resolution of inflammatory episodes, and may exacerbate adverse pathologies in response to infection. We investigated PMN cell death mechanisms following infection by virulent group A Streptococcus (GAS). Human PMNs were infected in vitro with a clinical, virulent GAS isolate and an avirulent derivative strain, and compared for phagocytosis, the production of reactive oxygen species (ROS), mitochondrial membrane depolarization and apoptotic markers. C57BL/6J mice were then infected, in order to observe the effects on murine PMNs in vivo. Human PMNs phagocytosed virulent GAS less efficiently, produced less ROS and underwent reduced mitochondrial membrane depolarization compared with phagocytosis of avirulent GAS. Morphological and biochemical analyses revealed that PMNs infected with avirulent GAS exhibited nuclear fragmentation and caspase-3 activation consistent with an anti-inflammatory apoptotic phenotype. Conversely, virulent GAS induced PMN vacuolization and plasma membrane permeabilization, leading to a necrotic form of cell death. Infection of the mice with virulent GAS engendered significantly higher systemic pro-inflammatory cytokine release and localized infiltration of murine PMNs, with cells associated with virulent GAS infection exhibiting reduced apoptotic potential. Avirulent GAS infection was associated with lower levels of proinflammatory cytokines and tissue PMN apoptosis. We propose that the differences in PMN cell death mechanisms influence the inflammatory responses to infection by GAS.