Group A Streptococcal DNase Sda1 Impairs Plasmacytoid Dendritic Cells' Type 1 Interferon Response

The burden of group A Streptococcus (GAS) infections: The challenge continues in the twenty-first century

Streptococcus pyogenes is a Gram-positive bacterium, also known as Group A Streptococcus (GAS), that has become a significant threat to the healthcare system, infecting more than 18 million people and resulting in more than 500,000 deaths annually worldwide. GAS infection rates decreased gradually during the 20th century in Western countries, largely due to improved living conditions and access to antibiotics. However, post-COVID-19, the situation has led to a steep increase in GAS infection rates in Europe, the United States, Australia, and New Zealand, which triggers a global concern. GAS infections are normally moderate, with symptoms of fever, pharyngitis, and pyoderma; nevertheless, if left untreated or with continued exposure to GAS or with recurring infections it can result in fatal outcomes. GAS produces a variety of virulence factors and exotoxins that can lead to deadly infections such as necrotizing fasciitis, impetigo, cellulitis, pneumonia, empyema, streptococcal toxic shock syndrome, bacteremia, and puerperal sepsis. In addition, post-immune mediated disorders such as post-streptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease contribute to extremely high death rates in developing nations. Despite substantial research on GAS infections, it is still unclear what molecular pathways are responsible for their emergence and how to best manage them. This review thus provides insights into the most recent research on the pathogenesis, virulence, resistance, and host interaction mechanisms of GAS, as well as novel management options to assist scientific communities in combating GAS infections.

Nosocomial Transmission of Necrotizing Fasciitis: A Molecular Characterization of Group A Streptococcal DNases in Clinical Virulence

Streptococcus pyogenes, or Group A Streptococcus (GAS), is responsible for over 500,000 deaths per year. Approximately 15% of these deaths are caused by necrotizing soft-tissue infections. In 2008, we isolated an M5 GAS, named the LO1 strain, responsible for the nosocomial transmission of necrotizing fasciitis between a baby and a nurse in Belgium. To understand this unusual transmission route, the LO1 strain was sequenced. A comparison of the LO1 genome and transcriptome with the reference M5 Manfredo strain was conducted. We found that the major differences were the presence of an additional DNase and a Tn916-like transposon in the LO1 and other invasive M5 genomes. RNA-seq analysis showed that genes present on the transposon were barely expressed. In contrast, the DNases presented different expression profiles depending on the tested conditions. We generated knock-out mutants in the LO1 background and characterized their virulence phenotype. We also determined their nuclease activity on different substrates. We found that DNases are dispensable for biofilm formation and adhesion to both keratinocytes and pharyngeal cells. Three of these were found to be essential for blood survival; Spd4 and Sdn are implicated in phagocytosis resistance, and Spd1 is responsible for neutrophil extracellular trap (NET) degradation.

RNA-seq analysis of chlorogenic acid intervention in duck embryo fibroblasts infected with duck plague virus

INTRODUCTION

Chlorogenic acid, the primary active component in Chinese medicines like honeysuckle, exhibits anti-inflammatory and antiviral effects. It has been demonstrated that chlorogenic acid effectively prevents and treats Duck enteritis virus (DEV) infection. This study aims to further elucidate the mechanism by which chlorogenic acid prevents DEV infection.

METHODS

Duck embryo fibroblast (DEF) cells were pre-treated with chlorogenic acid before being infected with DEV. Cell samples were collected at different time points for transcriptomic sequencing, while qPCR was used to detect the proliferation of DEV. Additionally, 30-day-old ducks were treated with chlorogenic acid, and their lymphoid organs were harvested for histopathological sections to observe pathological damage. The proliferation of DEV in the lymphoid organs was also detected using qPCR Based on the transcriptomic sequencing results, NF-κB1 gene was silenced by RNAi technology to analyze the effect of NF-κB1 gene on DEV proliferation.

RESULTS

Compared to the viral infection group, DEF cells in the chlorogenic acid intervention group exhibited significantly reduced DEV load (P < 0.05). Transcriptomic sequencing results suggested that chlorogenic acid inhibited DEV proliferation in DEF cells by regulating NF-κB signaling pathway. The results of RNAi silencing suggested that in the three treatment groups, compared with the DEV experimental group, there was no significant difference in the effect of pre-transfection after transfection on DEV proliferation, while both the pre-transfection after transfection and the simultaneous transfection group showed significant inhibition on DEV proliferation Furthermore, compared to the virus infection group, ducks in the chlorogenic acid intervention group showed significantly decreased DEV load in their lymphoid organs (P < 0.05), along with alleviated pathological damage such as nuclear pyretosis and nuclear fragmentation.

CONCLUSIONS

Chlorogenic acid effectively inhibits DEV proliferation in DEF and duck lymphatic organs, mitigates viral-induced pathological damage, and provides a theoretical basis for screening targeted drugs against DEV.

Reduced interleukin-18 secretion by human monocytic cells in response to infections with hyper-virulent Streptococcus pyogenes

BACKGROUND

Streptococcus pyogenes (group A streptococcus, GAS) causes a variety of diseases ranging from mild superficial infections of the throat and skin to severe invasive infections, such as necrotizing soft tissue infections (NSTIs). Tissue passage of GAS often results in mutations within the genes encoding for control of virulence (Cov)R/S two component system leading to a hyper-virulent phenotype. Dendritic cells (DCs) are innate immune sentinels specialized in antigen uptake and subsequent T cell priming. This study aimed to analyze cytokine release by DCs and other cells of monocytic origin in response to wild-type and natural covR/S mutant infections.

METHODS

Human primary monocyte-derived (mo)DCs were used. DC maturation and release of pro-inflammatory cytokines in response to infections with wild-type and covR/S mutants were assessed via flow cytometry. Global proteome changes were assessed via mass spectrometry. As a proof-of-principle, cytokine release by human primary monocytes and macrophages was determined.

RESULTS

In vitro infections of moDCs and other monocytic cells with natural GAS covR/S mutants resulted in reduced secretion of IL-8 and IL-18 as compared to wild-type infections. In contrast, moDC maturation remained unaffected. Inhibition of caspase-8 restored secretion of both molecules. Knock-out of streptolysin O in GAS strain with unaffected CovR/S even further elevated the IL-18 secretion by moDCs. Of 67 fully sequenced NSTI GAS isolates, 28 harbored mutations resulting in dysfunctional CovR/S. However, analyses of plasma IL-8 and IL-18 levels did not correlate with presence or absence of such mutations.

CONCLUSIONS

Our data demonstrate that strains, which harbor covR/S mutations, interfere with IL-18 and IL-8 responses in monocytic cells by utilizing the caspase-8 axis. Future experiments aim to identify the underlying mechanism and consequences for NSTI patients.

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.

The mechanism of HMGB1 secretion and release

High mobility group box 1 (HMGB1) is a nonhistone nuclear protein that has multiple functions according to its subcellular location. In the nucleus, HMGB1 is a DNA chaperone that maintains the structure and function of chromosomes. In the cytoplasm, HMGB1 can promote autophagy by binding to BECN1 protein. After its active secretion or passive release, extracellular HMGB1 usually acts as a damage-associated molecular pattern (DAMP) molecule, regulating inflammation and immune responses through different receptors or direct uptake. The secretion and release of HMGB1 is fine-tuned by a variety of factors, including its posttranslational modification (e.g., acetylation, ADP-ribosylation, phosphorylation, and methylation) and the molecular machinery of cell death (e.g., apoptosis, pyroptosis, necroptosis, alkaliptosis, and ferroptosis). In this minireview, we introduce the basic structure and function of HMGB1 and focus on the regulatory mechanism of HMGB1 secretion and release. Understanding these topics may help us develop new HMGB1-targeted drugs for various conditions, especially inflammatory diseases and tissue damage.

A nuclear protein that gets released after cell death or is actively secreted by immune cells offers a promising therapeutic target for treating diseases linked to excessive inflammation. Daolin Tang from the University of Texas Southwestern Medical Center in Dallas, USA, and colleagues review how cellular stresses can trigger the accumulation of HMGB1, a type of alarm signal protein that promotes the recruitment and activation of inflammation-promoting immune cells. The researchers discuss various mechanisms that drive both passive and active release of HMGB1 into the space around cells. These processes, which include enzymatic modifications of the HMGB1 protein, cell–cell interactions and molecular pathways of cell death, could be targeted by drugs to lessen tissue damage and inflammatory disease caused by HMGB1-induced immune responses

Immunity to Sda1 Protects against Infection by Sda1+ and Sda1- Serotypes of Group A Streptococcus

Group A Streptococcus (GAS) causes a variety of diseases globally. The DNases in GAS promote GAS evasion of neutrophil killing by degrading neutrophil extracellular traps (NETs). Sda1 is a prophage-encoded DNase associated with virulent GAS strains. However, protective immunity against Sda1 has not been determined. In this study, we explored the potential of Sda1 as a vaccine candidate. Sda1 was used as a vaccine to immunize mice intranasally. The effect of anti-Sda1 IgG in neutralizing degradation of NETs was determined and the protective role of Sda1 was investigated with intranasal and systemic challenge models. Antigen-specific antibodies were induced in the sera and pharyngeal mucosal site after Sda1 immunization. The anti-Sda1 IgG efficiently prevented degradation of NETs by supernatant samples from different GAS serotypes with or without Sda1. Sda1 immunization promoted clearance of GAS from the nasopharynx independent of GAS serotypes but did not reduce lethality after systemic GAS challenge. Anti-Sda1 antibody can neutralize degradation of NETs by Sda1 and other phage-encoded DNases and decrease GAS colonization at the nasopharynx across serotypes. These results indicate that Sda1 can be a potential vaccine candidate for reduction in GAS reservoir and GAS tonsillitis-associated diseases.

Molecular Characteristics of Streptococcus pyogenes Isolated From Chinese Children With Different Diseases

Streptococcus pyogenes is a bacterial pathogen that causes a wide spectrum of clinical diseases exclusively in humans. The distribution of emm type, antibiotic resistance and virulence gene expression for S. pyogenes varies temporally and geographically, resulting in distinct disease spectra. In this study, we analyzed antibiotic resistance and resistance gene expression patterns among S. pyogenes isolates from pediatric patients in China and investigated the relationship between virulence gene expression, emm type, and disease categories. Forty-two representative emm1.0 and emm12.0 strains (n = 20 and n = 22, respectively) isolated from patients with scarlet fever or obstructive sleep apnea-hypopnea syndrome were subjected to whole-genome sequencing and phylogenetic analysis. These strains were further analyzed for susceptibility to vancomycin. We found a high rate and degree of resistance to macrolides and tetracycline in these strains, which mainly expressed ermB and tetM. The disease category correlated with emm type but not superantigens. The distribution of vanuG and virulence genes were associated with emm type. Previously reported important prophages, such as φHKU16.vir, φHKU488.vir, Φ5005.1, Φ5005.2, and Φ5005.3 encoding streptococcal toxin, and integrative conjugative elements (ICEs) such as ICE-emm12 and ICE-HKU397 encoding macrolide and tetracycline resistance were found present amongst emm1 or emm12 clones from Shenzhen, China.

Impact of Type I Interferons on Susceptibility to Bacterial Pathogens

Interferons (IFNs) are a broad class of cytokines that have multifaceted roles. Type I IFNs have variable effects when it comes to host susceptibility to bacterial infections, that is, the resulting outcomes can be either protective or deleterious. The mechanisms identified to date have been wide and varied between pathogens. In this review, we discuss recent literature that provides new insights into the mechanisms of how type I IFN signaling exerts its effects on the outcome of infection from the host's point of view.

Pathogenic Mechanisms of Streptococcal Necrotizing Soft Tissue Infections

Necrotizing skin and soft tissue infections (NSTIs) are severe life-threatening and rapidly progressing infections. Beta-hemolytic streptococci, particularly S. pyogenes (group A streptococci (GAS)) but also S. dysgalactiae subsp. equisimilis (SDSE, most group G and C streptococcus), are the main causative agents of monomicrobial NSTIs and certain types, such as emm1 and emm3, are over-represented in NSTI cases. An arsenal of bacterial virulence factors contribute to disease pathogenesis, which is a complex and multifactorial process. In this chapter, we summarize data that have provided mechanistic and immuno-pathologic insight into host-pathogens interactions that contribute to tissue pathology in streptococcal NSTIs. The role of streptococcal surface associated and secreted factors contributing to the hyper-inflammatory state and immune evasion, bacterial load in the tissue and persistence strategies, including intracellular survival and biofilm formation, as well as strategies to mimic NSTIs in vitro are discussed.

Nucleases of bacterial pathogens as virulence factors, therapeutic targets and diagnostic markers

New frontiers of therapy are being explored against the upcoming bacterial diseases rendered untreatable due to multiple, extreme and pan- antibiotic resistance. Nucleases are ubiquitous in bacterial pathogens performing various functions like acquiring nucleotide nutrients, allowing or preventing uptake of foreign DNA, controlling biofilm formation/dispersal/architecture, invading host by tissue damage, evading immune defence by degrading DNA matrix of neutrophil extracellular traps (NETs) and immunomodulating the host immune response. Secretory nucleases also provide means of survival to other bacteria like iron-reducing Shewanella and such functions help them adapt and survive proficiently. Other than their pro-pathogen roles in survival, nucleases can be used directly as therapeutics. One of the powerful armours of pathogens is the formation of biofilms, thus helping them resist and persist in the harshest of environments. As eDNA forms the structural and binding component of biofilm, nucleases can be used against the adhering component, thus increasing the permeability of antimicrobial agents. Nucleases have recently become a model system of intense study for their biological functions and medical applications in diagnosis, immunoprophylaxis and therapy. Rational implications of these enzymes can impact human medicine positively in future by opening new ways for therapeutics which have otherwise reached saturation due to multi drug resistance.