Neutrophil-derived reactive agents induce a transient SpeB negative phenotype in Streptococcus pyogenes

Streptococcus pyogenes Activates Human Platelets via Streptolysin S-Mediated Calcium Ion Influx

INTRODUCTION

Streptococcus pyogenes (group A streptococcus, GAS) is an exclusively human pathogen. It causes a wide spectrum of diseases, ranging from mild infections such as pharyngitis to severe life-threatening conditions such as streptococcal toxic shock syndrome (STSS). Thrombocytopenia is a common feature of STSS and is associated with severe outcome. GAS produce a plethora of virulence factors, including streptolysin S (SLS), which has lytic as well as immunomodulatory properties. However, its role in platelet activation remains unclear.

METHODS

Washed human platelets were infected with GAS wild-type and SLS-deficient mutant (ΔsagA) strains. Platelet activation was assessed by measuring degranulation (CD62P expression). The role of calcium influx and the involvement of purinergic type 2 receptors (P2R) in platelet activation by GAS were assessed using chemical antagonists and calcium chelators.

RESULTS

GAS activate human platelets via SLS-mediated calcium influx, marked by increased surface expression of CD62P. IVIG treatment improved platelet viability in wild-type infections but failed to prevent SLS-mediated activation. Blocking of P2 receptors via suramin or NF449 as well as the use of calcium chelators reduced SLS-mediated platelet activation.

CONCLUSION

This study identified SLS as an M-protein and consequently a serotype-independent activator of human platelets. While IVIG partially improved platelet viability in GAS infections, its inability to prevent excessive platelet activation underscores the need for additional treatment options in severe GAS infections.

INTRODUCTION

Streptococcus pyogenes (group A streptococcus, GAS) is an exclusively human pathogen. It causes a wide spectrum of diseases, ranging from mild infections such as pharyngitis to severe life-threatening conditions such as streptococcal toxic shock syndrome (STSS). Thrombocytopenia is a common feature of STSS and is associated with severe outcome. GAS produce a plethora of virulence factors, including streptolysin S (SLS), which has lytic as well as immunomodulatory properties. However, its role in platelet activation remains unclear.

METHODS

Washed human platelets were infected with GAS wild-type and SLS-deficient mutant (ΔsagA) strains. Platelet activation was assessed by measuring degranulation (CD62P expression). The role of calcium influx and the involvement of purinergic type 2 receptors (P2R) in platelet activation by GAS were assessed using chemical antagonists and calcium chelators.

RESULTS

GAS activate human platelets via SLS-mediated calcium influx, marked by increased surface expression of CD62P. IVIG treatment improved platelet viability in wild-type infections but failed to prevent SLS-mediated activation. Blocking of P2 receptors via suramin or NF449 as well as the use of calcium chelators reduced SLS-mediated platelet activation.

CONCLUSION

This study identified SLS as an M-protein and consequently a serotype-independent activator of human platelets. While IVIG partially improved platelet viability in GAS infections, its inability to prevent excessive platelet activation underscores the need for additional treatment options in severe GAS infections.

Streptokinase reduces Streptococcus dysgalactiae subsp. equisimilis biofilm formation

BACKGROUND

Streptococcus dysgalactiae subspecies equisimilis (SDSE) is increasingly recognized as an emerging cause of invasive diseases including necrotizing soft tissue infections (NSTIs). In contrast to the closely related Streptococcus pyogenes, SDSE infections mainly affect older and comorbid patients. Biofilm formation has been demonstrated in soft tissue biopsies of S. pyogenes NSTI cases.

RESULTS

Here, we show that bacterial aggregations indicative of biofilms are also present in SDSE NSTI. Although streptokinase (Ska) activity and biofilm formation did not correlate in a diverse set of clinical SDSE isolates, addition of exogenous Ska at an early time point prevented biofilm formation for selected strains. Deletion of ska in SDSE S118 strain resulted in increased biofilm forming capacity. Ska-deficient mutant strain was characterized by a higher metabolic activity and consequent metabolome profiling of biofilms identified higher deposition of a wide range of metabolites as compared to the wild-type.

CONCLUSIONS

Our results argue that Ska suppresses biofilm formation in SDSE independent of its original plasminogen converting activity. However, the impact of biofilms and its consequences for patient outcomes in streptococcal NSTIs remain to be elucidated.

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.

Group A Streptococcus interactions with the host across time and space

Group A Streptococcus (GAS) has a fantastically wide tissue tropism in humans, manifesting as different diseases depending on the strain's virulence factor repertoire and the tissue involved. Activation of immune cells and pro-inflammatory signaling has historically been considered an exclusively host-protective response that a pathogen would seek to avoid. However, recent advances in human and animal models suggest that in some tissues, GAS will activate and manipulate specific pro-inflammatory pathways to promote growth, nutrient acquisition, persistence, recurrent infection, competition with other microbial species, dissemination, and transmission. This review discusses molecular interactions between the host and pathogen to summarize how infection varies across tissue and stages of inflammation. A need for inflammation for GAS survival during common, mild infections may drive selection for mechanisms that cause pathological and excess inflammation severe diseases such as toxic shock syndrome, necrotizing fasciitis, and rheumatic heart disease.