The contribution of group A streptococcal virulence determinants to the pathogenesis of sepsis

Increasing Rate of Fatal Streptococcus pyogenes Bacteriemia-A Challenge for Prompt Diagnosis and Appropriate Therapy in Real Praxis

Streptococcus pyogenes, group A streptococci (GAS) bacteriaemia, is a life-threatening infection with high mortality, requiring fast diagnosis together with the use of appropriate antibiotic therapy as soon as possible. Our study analysed data from 93 patients with GAS bacteraemia at the General University Hospital in Prague between January 2006 and March 2024. In the years 2016-2019 there was an increase in GAS bacteraemia. Mortality in the period 2006-2019 was 21.9%; in the period 2020-2024, the mortality increased to 41.4%, p = 0.08. At the same time, in the post-2020 period, the time from hospital admission to death was reduced from 9.5 days to 3 days. A significant predictor of worse outcome in this period was high levels of procalcitonin, >35.1 µg/L (100% sensitivity and 82.35% specificity), and lactate, >5 mmol/L (90.91% sensitivity and 91.67% specificity). Myoglobin was a significant predictor in both compared periods, the AUC was 0.771, p = 0.044, and the AUC was an even 0.889, p ≤ 0.001, respectively. All isolates of S. pyogenes were susceptible to penicillin, and resistance to clindamycin was 20.3% from 2006-2019 and 10.3% in 2020-2024. Appropriate therapy was initiated in 89.1%. and 96.6%, respectively. We hypothesise that the increase in mortality after 2020 might be due to a decrease in the immune status of the population.

AMPs as Host-Directed Immunomodulatory Agents against Skin Infections Caused by Opportunistic Bacterial Pathogens

Skin is the primary and largest protective organ of the human body. It produces a number of highly evolved arsenal of factors to counter the continuous assault of foreign materials and pathogens from the environment. One such potent factor is the repertoire of Antimicrobial Peptides (AMPs) that not only directly destroys invading pathogens, but also optimally modulate the immune functions of the body to counter the establishment and spread of infections. The canonical direct antimicrobial functions of these AMPs have been in focus for a long time to design principles for enhanced therapeutics, especially against the multi-drug resistant pathogens. However, in recent times the immunomodulatory functions performed by these peptides at sub-microbicidal concentrations have been a point of major focus in the field of host-directed therapeutics. Such strategies have the added benefit of not having the pathogens develop resistance against the immunomodulatory pathways, since the pathogens exploit these signaling pathways to obtain and survive within the host. Thus, this review summarizes the potent immunomodulatory effect of these AMPs on, specifically, the different host immune cells with the view of providing a platform of information that might help in designing studies to exploit and formulate effective host-directed adjunct therapeutic strategies that would synergies with drug regimens to counter the current diversity of drug-resistant skin opportunistic pathogens.

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.

Gasdermins in sepsis

Sepsis is a hyper-heterogeneous syndrome in which the systemic inflammatory response persists throughout the course of the disease and the inflammatory and immune responses are dynamically altered at different pathogenic stages. Gasdermins (GSDMs) proteins are pore-forming executors in the membrane, subsequently mediating the release of pro-inflammatory mediators and inflammatory cell death. With the increasing research on GSDMs proteins and sepsis, it is believed that GSDMs protein are one of the most promising therapeutic targets in sepsis in the future. A more comprehensive and in-depth understanding of the functions of GSDMs proteins in sepsis is important to alleviate the multi-organ dysfunction and reduce sepsis-induced mortality. In this review, we focus on the function of GSDMs proteins, the molecular mechanism of GSDMs involved in sepsis, and the regulatory mechanism of GSDMs-mediated signaling pathways, aiming to provide novel ideas and therapeutic strategies for the diagnosis and treatment of sepsis.

Knockdown of coagulation factor VII has potential anticoagulant and anti-inflammatory effects in a mouse model of group A streptococcal sepsis

Infections originating from subcutaneous tissues are among the most common invasive infections caused by group A streptococcus (GAS) and associated with systemic coagulation activation. The role of intrinsic coagulation factors on GAS virulence has recently been determined, but the role of the extrinsic coagulation factor VII is unknown. Using a mouse model, in which GAS-sepsis emerges from a subcutaneous infection, we show that FVII is a negative acute phase protein. F7 knockdown using antisense oligonucleotides resulted in an attenuated systemic coagulation activation and inflammatory response in septic animals. The findings indicate FVII's ability to modify the host response.

Correlates of immunity to Group A Streptococcus: a pathway to vaccine development

Understanding immunity in humans to Group A Streptococcus (Strep A) is critical for the development of successful vaccines to prevent the morbidity and mortality attributed to Strep A infections. Despite decades of effort, no licensed vaccine against Strep A exists and immune correlates of protection are lacking; a major impediment to vaccine development. In the absence of a vaccine, we can take cues from the development of natural immunity to Strep A in humans to identify immune correlates of protection. The age stratification of incidence of acute Strep A infections, peaking in young children and waning in early adulthood, coincides with the development of specific immune responses. Therefore, understanding the immune mechanisms involved in natural protection from acute Strep A infection is critical to identifying immune correlates to inform vaccine development. This perspective summarises the findings from natural infection studies, existing assays of immunity to Strep A, and highlights the gaps in knowledge to guide the development of Strep A vaccines and associated correlates of protection.

Methods to Analyze the Contribution of Complement Evasion Factor (CEF) to Streptococcus pyogenes Virulence

Group A Streptococcus (GAS, Streptococcus pyogenes) is an exclusively human pathogen that causes a range of diseases, including pharyngitis, tonsillitis, impetigo, erysipelas, necrotizing fasciitis, and toxic shock syndrome. Post-streptococcal sequelae include acute rheumatic fever and rheumatic heart disease. The bacterium produces a large arsenal of virulence factors that contribute to host tissue adhesion/colonization, bacterial spread, and host immune evasion. Immune evasion factors include proteins that interfere with complement, a system of plasma proteins that are activated by pathogens resulting in a variety of reactions on the surface of the pathogen. This leads to the activation of active components with a variety of effector functions, such as cell lysis, opsonization, and chemotaxis of phagocytes to the site of infection. We have recently identified a novel "complement evasion factor" (CEF) in S. pyogenes. CEF directly interacts with complement proteins C1r, C1s, C3, and C5, interrupts all three complement pathways, and prevents opsonization of the bacterial surface with C3b. We here present methods used to analyze the complement interference of CEF.

The Role of Host-Cellular Responses in COVID-19 Endothelial Dysfunction

SARS-CoV2, Severe acute respiratory syndrome coronavirus 2, is a novel member of the human coronavirus family that has recently emerged worldwide to cause COVID-19 disease. COVID-19 disease has been declared a worldwide pandemic with over 270 million total cases, and >5 million deaths as of this writing. Although co-morbidities and preexisting conditions have played a significant role in the severity of COVID-19, the hallmark feature of severe disease associated with SARS-CoV2 is respiratory failure. Recent findings have demonstrated a key role for endothelial dysfunction caused by SARS-CoV2 in these clinical outcomes, characterized by endothelial inflammation, the persistence of a pro-coagulative state, and major recruitment of leukocytes and other immune cells to localized areas of endothelial dysfunction. Though it is generally recognized that endothelial impairment is a major contributor to COVID-19 disease, studies to examine the initial cellular events involved in triggering endothelial dysfunction are needed. In this article, we review the general strategy of pathogens to exploit endothelial cells and the endothelium to cause disease. We discuss the role of the endothelium in COVID-19 disease and highlight very recent findings that identify key signaling and cellular events that are associated with the initiation of SARS-CoV2 infection. These studies may reveal specific molecular pathways that can serve as potential means of therapeutic development against COVID-19 disease.

Severe Acute Respiratory Syndrome Coronavirus-2 Pneumonia Presenting Concomitantly With Purpura Fulminans: A Case Report

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is a novel coronavirus that has been extensively described in its most common presentations. Its pathogenetic process is poorly understood, although it is theorized that endothelial damage and inflammation play a central role. Its prothrombotic nature affects multiple organs, including lungs, kidneys, and the central nervous system. Rarer are cutaneous presentations that can be triggered or displayed concomitantly with COVID-19. Purpura fulminans is a life-threatening syndrome that results in skin thrombosis and hemorrhagic infarction. While its association is explicit in critically ill patients with sepsis, few or rare cases have been described to be linked with COVID-19. In this report, we present a case of a critically ill patient with COVID-19 who showed signs of purpura fulminans while in the intensive care unit.

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.

Challenges in Surveillance for Streptococcal Toxic Shock Syndrome: Active Bacterial Core Surveillance, United States, 2014-2017

OBJECTIVES

Routine surveillance for streptococcal toxic shock syndrome (STSS), a severe manifestation of invasive group A Streptococcus (GAS) infections, likely underestimates its true incidence. The objective of our study was to evaluate routine identification of STSS in a national surveillance system for invasive GAS infections.

METHODS

Active Bacterial Core surveillance (ABCs) conducts active population-based surveillance for invasive GAS disease in selected US counties in 10 states. We categorized invasive GAS cases with a diagnosis of STSS made by a physician as STSS-physician and cases that met the Council of State and Territorial Epidemiologists (CSTE) clinical criteria for STSS based on data in the medical record as STSS-CSTE. We evaluated agreement between the 2 methods for identifying STSS and compared the estimated national incidence of STSS when applying proportions of STSS-CSTE and STSS-physician among invasive GAS cases from this study with national invasive GAS estimates for 2017.

RESULTS

During 2014-2017, of 7572 invasive GAS cases in ABCs, we identified 1094 (14.4%) as STSS-CSTE and 203 (2.7%) as STSS-physician, a 5.3-fold difference. Of 1094 STSS-CSTE cases, we identified only 132 (12.1%) as STSS-physician cases. Agreement between the 2 methods for identifying STSS was low (κ = 0.17; 95% CI, 0.14-0.19). Using ABCs data, we estimated 591 cases of STSS-physician and 3618 cases of STSS-CSTE occurred nationally in 2017.

CONCLUSIONS

We found a large difference in estimates of incidence of STSS when applying different surveillance methods and definitions. These results should help with better use of currently available surveillance data to estimate the incidence of STSS and to evaluate disease prevention efforts, in addition to guiding future surveillance efforts for STSS.

Systems Genetics Approaches in Mouse Models of Group A Streptococcal Necrotizing Soft-Tissue Infections

Mouse models are invaluable resources for studying the pathogenesis and preclinical evaluation of therapeutics and vaccines against many human pathogens. Infections caused by group A streptococcus (GAS, Streptococcus pyogenes) are heterogeneous ranging from mild pharyngitis to severe invasive necrotizing fasciitis, a subgroup of necrotizing soft-tissue infections (NSTIs). While several strains of mice including BALB/c, C3H/HeN, CBA/J, and C57BL/10 offered significant insights, the human specificity and the interindividual variations on susceptibility or resistance to GAS infections limit their ability to mirror responses as seen in humans. In this chapter, we discuss the advanced recombinant inbred (ARI) BXD mouse model that mimics the genetic diversity as seen in humans and underpins the feasibility to map multiple genes (genetic loci) modulating GAS NSTI. GAS produces a myriad of virulence factors, including superantigens (SAg). Superantigens are potent immune toxins that activate T cells by cross-linking T cell receptors with human leukocyte antigen class-II (HLA-II) molecules expressed on antigen-presenting cells. This leads to a pro-inflammatory cytokine storm and the subsequent multiple organ damage and shock. Inbred mice are innately refractive to SAg-mediated responses. In this chapter, we discuss the versatility of the HLA-II transgenic mouse model that allowed the biological validation of known genetic associations to GAS NSTI. The combined utility of ARI-BXD and HLA-II mice as complementary approaches that offer clinically translatable insights into pathomechanisms driven by complex traits and host genetic context and novel means to evaluate the in vivo efficiency of therapies to improve outcomes of GAS NSTI are also discussed.

Singularities of Pyogenic Streptococcal Biofilms - From Formation to Health Implication

Biofilms are generally defined as communities of cells involved in a self-produced extracellular matrix adhered to a surface. In biofilms, the bacteria are less sensitive to host defense mechanisms and antimicrobial agents, due to multiple strategies, that involve modulation of gene expression, controlled metabolic rate, intercellular communication, composition, and 3D architecture of the extracellular matrix. These factors play a key role in streptococci pathogenesis, contributing to therapy failure and promoting persistent infections. The species of the pyogenic group together with Streptococcus pneumoniae are the major pathogens belonging the genus Streptococcus, and its biofilm growth has been investigated, but insights in the genetic origin of biofilm formation are limited. This review summarizes pyogenic streptococci biofilms with details on constitution, formation, and virulence factors associated with formation.

Inflammatory Joint Disease Is a Risk Factor for Streptococcal Sepsis and Septic Arthritis in Mice

Septic arthritis is a medical emergency associated with high morbidity and mortality, yet hardly any novel advances exist for its clinical management. Despite septic arthritis being a global health burden, experimental data uncovering its etiopathogenesis remain scarce. In particular, any interplay between septic arthritis and preceding joint diseases are unknown as is the contribution of the synovial membrane to the onset of inflammation. Using C57BL/6 mice as a model to study sepsis, we discovered that Group A Streptococcus (GAS) – an important pathogen causing septic arthritis - was able to invade the articular microenvironment. Bacterial invasion resulted in the infiltration of immune cells and detrimental inflammation. In vitro infected fibroblast-like synoviocytes induced the expression of chemokines (Ccl2, Cxcl2), inflammatory cytokines (Tnf, Il6), and integrin ligands (ICAM-1, VCAM-1). Apart from orchestrating immune cell attraction and retention, synoviocytes also upregulated mediators impacting on bone remodeling (Rankl) and cartilage integrity (Mmp13). Using collagen-induced arthritis in DBA/1 × B10.Q F1 mice, we could show that an inflammatory joint disease exacerbated subsequent septic arthritis which was associated with an excessive release of cytokines and eicosanoids. Importantly, the severity of joint inflammation controlled the extent of bone erosions during septic arthritis. In order to ameliorate septic arthritis, our results suggest that targeting synoviocytes might be a promising approach when treating patients with inflammatory joint disease for sepsis.

Phosphotransferase System Uptake and Metabolism of the β-Glucoside Salicin Impact Group A Streptococcal Bloodstream Survival and Soft Tissue Infection

Streptococcus pyogenes (group A Streptococcus [GAS]), a major human-specific pathogen, relies on efficient nutrient acquisition for successful infection within its host. The phosphotransferase system (PTS) couples the import of carbohydrates with their phosphorylation prior to metabolism and has been linked to GAS pathogenesis. In a screen of an insertional mutant library of all 14 annotated PTS permease (EIIC) genes in MGAS5005, the annotated β-glucoside PTS transporter (bglP) was found to be crucial for GAS growth and survival in human blood and was validated in another M1T1 GAS strain, 5448. In 5448, bglP was shown to be in an operon with a putative phospho-β-glucosidase (bglB) downstream and a predicted antiterminator (licT) upstream. Using defined nonpolar mutants of the β-glucoside permease (bglP) and β-glucosidase enzyme (bglB) in 5448, we showed that bglB, not bglP, was important for growth in blood. Furthermore, transcription of the licT-blgPB operon was found to be repressed by glucose and induced by the β-glucoside salicin as the sole carbon source. Investigation of the individual bglP and bglB mutants determined that they influence in vitro growth in the β-glucoside salicin; however, only bglP was necessary for growth in other non-β-glucoside PTS sugars, such as fructose and mannose. Additionally, loss of BglP and BglB suggests that they are important for the regulation of virulence-related genes that control biofilm formation, streptolysin S (SLS)-mediated hemolysis, and localized ulcerative lesion progression during subcutaneous infections in mice. Thus, our results indicate that the β-glucoside PTS transports salicin and its metabolism can differentially influence GAS pathophysiology during soft tissue infection.

The scfCDE Operon Encodes a Predicted ABC Importer Required for Fitness and Virulence during Group A Streptococcus Invasive Infection

As a strict human pathogen, Streptococcus pyogenes (group A Streptococcus, or GAS) causes a wide range of infections, from superficial to life-threatening diseases, upon dissemination. Thus, it is necessary to gain a better understanding of how GAS successfully overcomes host-mediated challenges and infects various host niches. We previously identified subcutaneous fitness (scf) genes in the clinically relevant wild-type (WT) GAS M1T1 5448 strain that are critical for fitness during murine soft-tissue infection at both 24 h and 48 h postinfection. The uncharacterized locus scfCDE was transcribed as an operon and is predicted to encode an ABC importer for nutrient uptake (e.g., amino acids). Individual scfCDE deletion mutants grew comparably to WT 5448 in rich medium but exhibited reduced fitness during competitive growth in murine soft tissue and in nutrient-limiting chemically defined medium (CDM). A deletion of the permease gene scfD resulted in a monoculture growth defect in CDM that could be rescued by addition of excess peptides, suggesting a role as an amino acid importer. Interestingly, the ΔscfC substrate-binding and ΔscfD permease mutants, but not the ΔscfE ATPase mutant, were highly attenuated in murine soft tissue. Moreover, all three genes were required for GAS survival in human blood, indicating their impact is not limited to superficial infections. As such, scfCDE plays an integral role in enhancing GAS adaptation during localized infection as well as dissemination to deeper host environments. Since scfCDE is conserved throughout Firmicutes, this work may contribute to the development of therapeutic strategies against GAS and other Gram-positive pathogens.

Streptococcal toxic shock syndrome caused by β-hemolytic streptococci: Clinical features and cytokine and chemokine analyses of 15 cases

OBJECTIVES

β-Hemolytic streptococci occasionally cause severe infections such as necrotizing fasciitis and streptococcal toxic shock syndrome (STSS). Here, we conducted a prospective study to investigate the production of cytokines and chemokines in patients with STSS to explore its pathogenesis in survivors and fatal cases.

METHODS

From January 2013 through August 2015, all culture results from normally sterile sites were prospectively followed and screened for STSS. Clinical characteristics of the patients with STSS were evaluated and compared between survivors and fatal cases. Serum samples were collected on admission for quantification of various cytokines and chemokines. Bacterial strains were categorized by Lancefield grouping and analyzed for the emm type, and presence of speA, speB, speC, and speF.

RESULTS

Fifteen patients received diagnosis of STSS. The median age of the patients was 60-year-old, and the mortality rate was 40% despite intensive treatment. Nine strains were categorized as group A, two belonged to group G, and four to group B. Group A contained various emm genotypes. Unexpectedly, potent proinflammatory cytokine levels such as TNF-α and IL-1β were not significantly elevated, and comparison with surviving patients showed that IL-6, IL-8, and MCP-1 levels were significantly decreased and creatine kinase level was significantly elevated in fatally ill cases.

CONCLUSION

Our results indicate that reduced production of proinflammatory cytokines and chemokines may be involved in STSS pathogenesis and critical for prognosis of patients with STSS.

Complement Activation as a Helping Hand for Inflammophilic Pathogens and Cancer

The complement system, an evolutionarily ancient component of innate immunity, is capable of protecting hosts from invading pathogens, either directly, by lysis of target cells, or indirectly, by mobilization of host immune mechanisms. However, this potentially cytotoxic cascade must be tightly regulated, since improperly controlled complement can damage healthy cells and tissues. The practical importance of this axis is highlighted when impairment of complement regulators or bacterial mechanisms of complement evasion result in pathogenic conditions. Recognition of complement as a "double-edged sword" is widely acknowledged, but another, currently underappreciated aspect of complement function has emerged as an important player in homeostatic balance-the dual outcome of complement-mediated inflammation. In most cases, the proinflammatory properties of complement are beneficial to the host. However, certain pathogens have developed the ability to utilize local inflammation as a source of nutrients and as a way to establish a niche for further colonization. Such a strategy can be illustrated in the example of periodontitis. Interestingly, certain tumors also seem to benefit from complement activation products, which promote a proangiogenic and immunosuppressive microenvironment.

Streptococcus pyogenes-purpura fulminans as an invasive form of group A streptococcal infection

BACKGROUND

Streptococcus pyogenes is an uncommon pathogen of purpura fulminans, and the pathogenesis of S. pyogenes-purpura fulminans remains unclear because of paucity of cases. We reported a pediatric case of S. pyogenes-purpura fulminans with literature review of the disease.

CASE PRESENTATION

A 3-year-old boy showed limping, lethargy and acral gangrene within 24 h. A diagnosis of S. pyogenes-purpura fulminans was made for bacterial isolation from throat and peripheral blood. Intensive therapy led to a survival with amputation of the left distal metatarsal bone, and normal development. The isolated M12 carried no mutation of csrS/R or rgg. Thrombophilia or immunodeficiency was excluded.

DISCUSSION

Twelve-reported cases (9 pediatric and 3 elderly) of S. pyogenes-purpura fulminans started with shock and coagulopathy. Five patients age < 8 years had no underlying disease and survived. One youngest and two immunocompromised patients died.

CONCLUSION

Streptococcus pyogenes-acute infectious purpura fulminans is a distinctive rare form of aggressive GAS infections.

Bacterial genome sequencing in clinical microbiology: a pathogen-oriented review

In recent years, whole-genome sequencing (WGS) has been perceived as a technology with the potential to revolutionise clinical microbiology. Herein, we reviewed the literature on the use of WGS for the most commonly encountered pathogens in clinical microbiology laboratories: Escherichia coli and other Enterobacteriaceae, Staphylococcus aureus and coagulase-negative staphylococci, streptococci and enterococci, mycobacteria and Chlamydia trachomatis. For each pathogen group, we focused on five different aspects: the genome characteristics, the most common genomic approaches and the clinical uses of WGS for (i) typing and outbreak analysis, (ii) virulence investigation and (iii) in silico antimicrobial susceptibility testing. Of all the clinical usages, the most frequent and straightforward usage was to type bacteria and to trace outbreaks back. A next step toward standardisation was made thanks to the development of several new genome-wide multi-locus sequence typing systems based on WGS data. Although virulence characterisation could help in various particular clinical settings, it was done mainly to describe outbreak strains. An increasing number of studies compared genotypic to phenotypic antibiotic susceptibility testing, with mostly promising results. However, routine implementation will preferentially be done in the workflow of particular pathogens, such as mycobacteria, rather than as a broadly applicable generic tool. Overall, concrete uses of WGS in routine clinical microbiology or infection control laboratories were done, but the next big challenges will be the standardisation and validation of the procedures and bioinformatics pipelines in order to reach clinical standards.

Genome-wide discovery of novel M1T1 group A streptococcal determinants important for fitness and virulence during soft-tissue infection

The Group A Streptococcus remains a significant human pathogen causing a wide array of disease ranging from self-limiting to life-threatening invasive infections. Epithelium (skin or throat) colonization with progression to the subepithelial tissues is the common step in all GAS infections. Here, we used transposon-sequencing (Tn-seq) to define the GAS 5448 genetic requirements for in vivo fitness in subepithelial tissue. A near-saturation transposon library of the M1T1 GAS 5448 strain was injected subcutaneously into mice, producing suppurative inflammation at 24 h that progressed to prominent abscesses with tissue necrosis at 48 h. The library composition was monitored en masse by Tn-seq and ratios of mutant abundance comparing the output (12, 24 and 48 h) versus input (T₀) mutant pools were calculated for each gene. We identified a total of 273 subcutaneous fitness (scf) genes with 147 genes (55 of unknown function) critical for the M1T1 GAS 5448 fitness in vivo; and 126 genes (53 of unknown function) potentially linked to in vivo fitness advantage. Selected scf genes were validated in competitive subcutaneous infection with parental 5448. Two uncharacterized genes, scfA and scfB, encoding putative membrane-associated proteins and conserved among Gram-positive pathogens, were further characterized. Defined scfAB mutants in GAS were outcompeted by wild type 5448 in vivo, attenuated for lesion formation in the soft tissue infection model and dissemination to the bloodstream. We hypothesize that scfAB play an integral role in enhancing adaptation and fitness of GAS during localized skin infection, and potentially in propagation to other deeper host environments.

The WHO ranks the Group A Streptococcus (GAS) in the top 10 leading causes of morbidity and mortality from infectious diseases worldwide. GAS is a strict human pathogen causing both benign superficial infections as well as life-threatening invasive diseases. All GAS infections begin by colonization of an epithelium (throat or skin) followed by propagation into subepithelial tissues. The genetic requirements for M1T1 GAS 5448 within this niche were interrogated by in vivo transposon sequencing (Tn-seq), identifying 273 subcutaneous fitness (scf) genes with 108 of those previously of “unknown function”. Two yet uncharacterized genes, scfA and scfB, were shown to be critical during GAS 5448 soft tissue infection and dissemination into the bloodstream. Thus, this study improves the functional annotation of the GAS genome, providing new insights into GAS pathophysiology and enhancing the development of novel GAS therapeutics.

MAIT cells launch a rapid, robust and distinct hyperinflammatory response to bacterial superantigens and quickly acquire an anergic phenotype that impedes their cognate antimicrobial function: Defining a novel mechanism of superantigen-induced immunopathology and immunosuppression

Superantigens (SAgs) are potent exotoxins secreted by Staphylococcus aureus and Streptococcus pyogenes. They target a large fraction of T cell pools to set in motion a "cytokine storm" with severe and sometimes life-threatening consequences typically encountered in toxic shock syndrome (TSS). Given the rapidity with which TSS develops, designing timely and truly targeted therapies for this syndrome requires identification of key mediators of the cytokine storm's initial wave. Equally important, early host responses to SAgs can be accompanied or followed by a state of immunosuppression, which in turn jeopardizes the host's ability to combat and clear infections. Unlike in mouse models, the mechanisms underlying SAg-associated immunosuppression in humans are ill-defined. In this work, we have identified a population of innate-like T cells, called mucosa-associated invariant T (MAIT) cells, as the most powerful source of pro-inflammatory cytokines after exposure to SAgs. We have utilized primary human peripheral blood and hepatic mononuclear cells, mouse MAIT hybridoma lines, HLA-DR4-transgenic mice, MAIThighHLA-DR4+ bone marrow chimeras, and humanized NOD-scid IL-2Rγnull mice to demonstrate for the first time that: i) mouse and human MAIT cells are hyperresponsive to SAgs, typified by staphylococcal enterotoxin B (SEB); ii) the human MAIT cell response to SEB is rapid and far greater in magnitude than that launched by unfractionated conventional T, invariant natural killer T (iNKT) or γδ T cells, and is characterized by production of interferon (IFN)-γ, tumor necrosis factor (TNF)-α and interleukin (IL)-2, but not IL-17A; iii) high-affinity MHC class II interaction with SAgs, but not MHC-related protein 1 (MR1) participation, is required for MAIT cell activation; iv) MAIT cell responses to SEB can occur in a T cell receptor (TCR) Vβ-specific manner but are largely contributed by IL-12 and IL-18; v) as MAIT cells are primed by SAgs, they also begin to develop a molecular signature consistent with exhaustion and failure to participate in antimicrobial defense. Accordingly, they upregulate lymphocyte-activation gene 3 (LAG-3), T cell immunoglobulin and mucin-3 (TIM-3), and/or programmed cell death-1 (PD-1), and acquire an anergic phenotype that interferes with their cognate function against Klebsiella pneumoniae and Escherichia coli; vi) MAIT cell hyperactivation and anergy co-utilize a signaling pathway that is governed by p38 and MEK1/2. Collectively, our findings demonstrate a pathogenic, rather than protective, role for MAIT cells during infection. Furthermore, we propose a novel mechanism of SAg-associated immunosuppression in humans. MAIT cells may therefore provide an attractive therapeutic target for the management of both early and late phases of severe SAg-mediated illnesses.

The Transcriptional Regulator CpsY Is Important for Innate Immune Evasion in Streptococcus pyogenes

As an exclusively human pathogen, Streptococcus pyogenes (the group A streptococcus [GAS]) has specifically adapted to evade host innate immunity and survive in multiple tissue niches, including blood. GAS can overcome the metabolic constraints of the blood environment and expresses various immunomodulatory factors necessary for survival and immune cell resistance. Here we present our investigation of one such factor, the predicted LysR family transcriptional regulator CpsY. The encoding gene, cpsY, was initially identified as being required for GAS survival in a transposon-site hybridization (TraSH) screen in whole human blood. CpsY is homologous with transcriptional regulators of Streptococcus mutans (MetR), Streptococcus iniae (CpsY), and Streptococcus agalactiae (MtaR) that regulate methionine transport, amino acid metabolism, resistance to neutrophil-mediated killing, and survival in vivo Our investigation indicated that CpsY is involved in GAS resistance to innate immune cells of its human host. However, GAS CpsY does not manifest the in vitro phenotypes of its homologs in other streptococcal species. GAS CpsY appears to regulate a small set of genes that is markedly different from the regulons of its homologs. The differential expression of these genes depends on the growth medium, and CpsY modestly influences their expression. The GAS CpsY regulon includes known virulence factors (mntE, speB, spd, nga [spn], prtS [SpyCEP], and sse) and cell surface-associated factors of GAS (emm1, mur1.2, sibA [cdhA], and M5005_Spy0500). Intriguingly, the loss of CpsY in GAS does not result in virulence defects in murine models of infection, suggesting that CpsY function in immune evasion is specific to the human host.

Identification of a two-component Class IIb bacteriocin in Streptococcus pyogenes by recombinase-based in vivo expression technology

Streptococcus pyogenes is a globally prominent bacterial pathogen that exhibits strict tropism for the human host, yet bacterial factors responsible for the ability of S. pyogenes to compete within this limited biological niche are not well understood. Using an engineered recombinase-based in vivo expression technology (RIVET) system, we identified an in vivo-induced promoter region upstream of a predicted Class IIb bacteriocin system in the M18 serotype S. pyogenes strain MGAS8232. This promoter element was not active under in vitro laboratory conditions, but was highly induced within the mouse nasopharynx. Recombinant expression of the predicted mature S. pyogenes bacteriocin peptides (designated SpbM and SpbN) revealed that both peptides were required for antimicrobial activity. Using a gain of function experiment in Lactococcus lactis, we further demonstrated S. pyogenes immunity function is encoded downstream of spbN. These data highlight the importance of bacterial gene regulation within appropriate environments to help understand mechanisms of niche adaptation by bacterial pathogens.

Metabolic traits of pathogenic streptococci

Invasive and noninvasive diseases caused by facultative pathogenic streptococci depend on their equipment with virulence factors and on their ability to sense and adapt to changing nutrients in different host environments. The knowledge of the principal metabolic mechanisms which allow these bacteria to recognize and utilize nutrients in host habitats is a prerequisite for our understanding of streptococcal pathogenicity and the development of novel control strategies. This review aims to summarize and compare the central carbohydrate metabolic and amino acid biosynthetic pathways of a selected group of streptococcal species, all belonging to the naso-oropharyngeal microbiome in humans and/or animals. We also discuss the urgent need of comprehensive metabolomics approaches for a better understanding of the streptococcal metabolism during host-pathogen interaction.

Emergence of a novel lineage containing a prophage in emm/M3 group A Streptococcus associated with upsurge in invasive disease in the UK

A sudden increase in invasive Group A Streptococcus (iGAS) infections associated with emm/M3 isolates during the winter of 2008/09 prompted the initiation of enhanced surveillance in England. In order to characterise the population of emm/M3 GAS within the UK and determine bacterial factors that might be responsible for this upsurge, 442 emm/M3 isolates from cases of invasive and non-invasive infections during the period 2001-2013 were subjected to whole genome sequencing. MLST analysis differentiated emm/M3 isolates into three sequence types (STs): ST15, ST315 and ST406. Analysis of the whole genome SNP-based phylogeny showed that the majority of isolates from the 2008-2009 upsurge period belonged to a distinct lineage characterized by the presence of a prophage carrying the speC exotoxin and spd1 DNAase genes but loss of two other prophages considered typical of the emm/M3 lineage. This lineage was significantly associated with the upsurge in iGAS cases and we postulate that the upsurge could be attributed in part to expansion of this novel prophage-containing lineage within the population. The study underlines the importance of prompt genomic analysis of changes in the GAS population, providing an advanced public health warning system for newly emergent, pathogenic strains.

Inferring Infection Patterns Based on a Connectivity Map of Host Transcriptional Responses

Host responses to infections represent an important pathogenicity determiner, and delineation of host responses can elucidate pathogenesis processes and inform the development of anti-infection therapies. Low cost, high throughput, easy quantitation, and rich descriptions have made gene expression profiling generated by DNA microarrays an optimal approach for describing host transcriptional responses (HTRs). However, efforts to characterize the landscape of HTRs to diverse pathogens are far from offering a comprehensive view. Here, we developed an HTR Connectivity Map based on systematic assessment of pairwise similarities of HTRs to 50 clinically important human pathogens using 1353 gene-expression profiles generated from >60 human cells/tissues. These 50 pathogens were further partitioned into eight robust “HTR communities” (i.e., groups with more consensus internal HTR similarities). These communities showed enrichment in specific infection attributes and differential gene expression patterns. Using query signatures of HTRs to external pathogens, we demonstrated four distinct modes of HTR associations among different pathogens types/class, and validated the reliability of the HTR community divisions for differentiating and categorizing pathogens from a host-oriented perspective. These findings provide a first-generation HTR Connectivity Map of 50 diverse pathogens, and demonstrate the potential for using annotated HTR community to detect functional associations among infectious pathogens.

Invasive streptococcal disease: a review for clinicians

INTRODUCTION

Streptococci are a genus of Gram-positive bacteria which cause diverse human diseases. Many of these species have the potential to cause invasive infection resulting from the presence of bacteria in a normally sterile site.

SOURCES OF DATA

Original articles, reviews and guidelines.

AREAS OF AGREEMENT

Invasive infection by a streptococcus species usually causes life-threatening illness. When measured in terms of deaths, disability and cost, these infections remain an important threat to health in the UK. Overall they are becoming more frequent among the elderly and those with underlying chronic illness. New observational evidence has become available to support the use of clindamycin and intravenous immunoglobulin in invasive Group A streptococcal disease.

AREAS OF CONTROVERSY

Few interventions for the treatment and prevention of these infections have undergone rigorous evaluation in clinical trials. For example, the role of preventative strategies such as screening of pregnant women to prevent neonatal invasive Group B streptococcal disease needs to be clarified.

FUTURE PROSPECTS

Studies of invasive streptococcal disease are challenging to undertake, not least because individual hospitals treat relatively few confirmed cases. Instead clinicians and scientists must work together to build national and international networks with the aim of developing a more complete evidence base for the treatment and prevention of these devastating infections.

Evasion and interactions of the humoral innate immune response in pathogen invasion, autoimmune disease, and cancer

The humoral innate immune system is composed of three major branches, complement, coagulation, and natural antibodies. To persist in the host, pathogens, such as bacteria, viruses, and cancers must evade parts of the innate humoral immune system. Disruptions in the humoral innate immune system also play a role in the development of autoimmune diseases. This review will examine how Gram positive bacteria, viruses, cancer, and the autoimmune conditions systemic lupus erythematosus and anti-phospholipid syndrome, interact with these immune system components. Through examining evasion techniques it becomes clear that an interplay between these three systems exists. By exploring the interplay and the evasion/disruption of the humoral innate immune system, we can develop a better understanding of pathogenic infections, cancer, and autoimmune disease development.

Molecular and genomic characterization of pathogenic traits of group A Streptococcus pyogenes

Group A streptococcus (GAS) or Streptococcus pyogenes causes various diseases ranging from self-limiting sore throat to deadly invasive diseases. The genome size of GAS is 1.85-1.9 Mb, and genomic rearrangement has been demonstrated. GAS possesses various surface-associated substances such as hyaluronic capsule, M proteins, and fibronectin/laminin/immunoglobulin-binding proteins. These are related to the virulence and play multifaceted and mutually reflected roles in the pathogenesis of GAS infections. Invasion of GAS into epithelial cells and deeper tissues provokes immune and non-immune defense or inflammatory responses including the recruitment of neutrophils, macrophages, and dendritic cells in hosts. GAS frequently evades host defense mechanisms by using its virulence factors. Extracellular products of GAS may perturb cellular and subcellular functions and degrade tissues enzymatically, which leads to the aggravation of local and/or systemic disorders in the host. In this review, we summarize some important cellular and extracellular substances that may affect pathogenic processes during GAS infections, and the host responses to these.

RNA-mediated regulation in Gram-positive pathogens: an overview punctuated with examples from the group A Streptococcus

RNA-based mechanisms of regulation represent a ubiquitous class of regulators that are associated with diverse processes including nutrient sensing, stress response, modulation of horizontal gene transfer, and virulence factor expression. While better studied in Gram-negative bacteria, the literature is replete with examples of the importance of RNA-mediated regulatory mechanisms to the virulence and fitness of Gram-positives. Regulatory RNAs are classified as cis-acting, e.g. riboswitches, which modulate the transcription, translation, or stability of co-transcribed RNA, or trans-acting, e.g. small regulatory RNAs, which target separate mRNAs or proteins. The group A Streptococcus (GAS, Streptococcus pyogenes) is a Gram-positive bacterial pathogen from which several regulatory RNA mechanisms have been characterized. The study of RNA-mediated regulation in GAS has uncovered novel concepts with respect to how small regulatory RNAs may positively regulate target mRNA stability, and to how CRISPR RNAs are processed from longer precursors. This review provides an overview of RNA-mediated regulation in Gram-positive bacteria, and is highlighted with specific examples from GAS research. The key roles that these systems play in regulating bacterial virulence are discussed and future perspectives outlined.

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.

Gram-positive and gram-negative bacterial toxins in sepsis: a brief review

Bacterial sepsis is a major cause of fatality worldwide. Sepsis is a multi-step process that involves an uncontrolled inflammatory response by the host cells that may result in multi organ failure and death. Both gram-negative and gram-positive bacteria play a major role in causing sepsis. These bacteria produce a range of virulence factors that enable them to escape the immune defenses and disseminate to remote organs, and toxins that interact with host cells via specific receptors on the cell surface and trigger a dysregulated immune response. Over the past decade, our understanding of toxins has markedly improved, allowing for new therapeutic strategies to be developed. This review summarizes some of these toxins and their role in sepsis.