Invasive streptococcal infections

The Molecular Basis of Human IgG-Mediated Enhancement of C4b-Binding Protein Recruitment to Group A Streptococcus

Streptococcus pyogenes infects over 700 million people worldwide annually. Immune evasion strategies employed by the bacteria include binding of the complement inhibitors, C4b-binding protein (C4BP) and Factor H in a human-specific manner. We recently showed that human IgG increased C4BP binding to the bacterial surface, which promoted streptococcal immune evasion and increased mortality in mice. We sought to identify how IgG promotes C4BP binding to Protein H, a member of the M protein family. Dimerization of Protein H is pivotal for enhanced binding to human C4BP. First, we illustrated that Protein H, IgG, and C4BP formed a tripartite complex. Second, surface plasmon resonance revealed that Protein H binds IgG solely through Fc, but not Fab domains, and with high affinity (IgG-Protein H: K_D = 0.4 nM; IgG-Fc-Protein H: K_D ≤ 1.6 nM). Each IgG binds two Protein H molecules, while up to six molecules of Protein H bind one C4BP molecule. Third, interrupting Protein H dimerization either by raising temperature to 41°C or with a synthetic peptide prevented IgG-Protein H interactions. IgG-Fc fragments or monoclonal human IgG permitted maximal C4BP binding when used at concentrations from 0.1 to 10 mg/ml. In contrast, pooled human IgG enhanced C4BP binding at concentrations up to 1 mg/ml; decreased C4BP binding at 10 mg/ml occurred probably because of Fab-streptococcal interactions at these high IgG concentrations. Taken together, our data show how S. pyogenes exploits human IgG to evade complement and enhance its virulence. Elucidation of this mechanism could aid design of new therapeutics against S. pyogenes.

Complement Activation Occurs at the Surface of Platelets Activated by Streptococcal M1 Protein and This Results in Phagocytosis of Platelets

Platelets circulate the bloodstream and principally maintain hemostasis. Disturbed hemostasis, a dysregulated inflammatory state, and a decreased platelet count are all hallmarks of severe invasive Streptococcus pyogenes infection, sepsis. We have previously demonstrated that the released M1 protein from S. pyogenes activates platelets, and this activation is dependent on the binding of M1 protein, fibrinogen, and M1-specific IgG to platelets in susceptible donors. In this study, we characterize the M1-associated protein interactions in human plasma and investigate the acquisition of proteins to the surface of activated platelets and the consequences for platelet immune function. Using quantitative mass spectrometry, M1 protein was determined to form a protein complex in plasma with statistically significant enrichment of fibrinogen, IgG3, and complement components, especially C1q. Using flow cytometry, these plasma proteins were also confirmed to be acquired to the platelet surface, resulting in complement activation on M1-activated human platelets. Furthermore, we demonstrated an increased phagocytosis of M1-activated platelets by monocytes, which was not observed with other physiological platelet agonists. This reveals a novel mechanism of complement activation during streptococcal sepsis, which contributes to the platelet consumption that occurs in sepsis.

Human IgG Increases Virulence of Streptococcus pyogenes through Complement Evasion

Streptococcus pyogenes is an exclusively human pathogen that can provoke mild skin and throat infections but can also cause fatal septicemia. This gram-positive bacterium has developed several strategies to evade the human immune system, enabling S. pyogenes to survive in the host. These strategies include recruiting several human plasma proteins, such as the complement inhibitor, C4b-binding protein (C4BP), and human (hu)-IgG through its Fc region to the bacterial surface to evade immune recognition. We identified a novel virulence mechanism whereby IgG-enhanced binding of C4BP to five of 12 tested S. pyogenes strains expressed diverse M proteins that are important surface-expressed virulence factors. Importantly, all strains that bound C4BP in the absence of IgG bound more C4BP when IgG was present. Further studies with an M1 strain that additionally expressed protein H, also a member of the M protein family, revealed that binding of hu-IgG Fc to protein H increased the affinity of protein H for C4BP. Increased C4BP binding accentuated complement downregulation, resulting in diminished bacterial killing. Accordingly, mortality from S. pyogenes infection in hu-C4BP transgenic mice was increased when hu-IgG or its Fc portion alone was administered concomitantly. Electron microscopy analysis of human tissue samples with necrotizing fasciitis confirmed increased C4BP binding to S. pyogenes when IgG was present. Our findings provide evidence of a paradoxical function of hu-IgG bound through Fc to diverse S. pyogenes isolates that increases their virulence and may counteract the beneficial effects of IgG opsonization.

Changes in the clinical and epidemiological features of group A streptococcal bacteraemia in Australia's Northern Territory

OBJECTIVE

Invasive group A streptococcus (iGAS) disease is an important cause of mortality globally. The incidence of iGAS in Australia's tropical Northern Territory (NT) has been previously reported as 32.2/100 000 in Indigenous people for the period 1991-1996. We aimed to measure the incidence and severity of iGAS disease in the NT since this time.

METHODS

We collected demographic data for all GAS blood culture isolates over a 12-year period (1998-2009) from the three hospital laboratories serving the tropical NT. We then collected detailed clinical information from hospital records and databases for the subset of these patients who were admitted to Royal Darwin Hospital during 2005-2009.

RESULTS

There were 295 confirmed cases of GAS bacteraemia over the study period, with a mean (SD) age of 42.1 (22.0) years, and 163 (55.0%) were male. The annual age-adjusted incidence was 15.2 (95% CI 13.4-16.9)/100 000 overall and 59.4 (95% CI 51.2-67.6) in Indigenous Australians. For 2005-2009, there were 123 cases with the most common focus of infection being skin/soft tissue [44 (35.6%)]; 29 patients (23.6%) required intensive care unit admission and 20 (16.3%) had streptococcal toxic shock syndrome. Antecedent sore throat or use of non-steroidal anti-inflammatory drugs was rare, but current or recent scabies, pyoderma and trauma were common.

CONCLUSION

The incidence and severity of iGAS are high and increasing in tropical northern Australia, and urgent attention is needed to improve surveillance and the social determinants of health in this population. This study adds to emerging data suggesting increasing importance of iGAS in low- and middle-income settings globally.

Platelet activation by Streptococcus pyogenes leads to entrapment in platelet aggregates, from which bacteria subsequently escape

Platelet activation and aggregation have been reported to occur in response to a number of Gram-positive pathogens. Here, we show that platelet aggregates induced by Streptococcus pyogenes were unstable and that viable bacteria escaped from the aggregates over time. This was not due to differential activation in response to the bacteria compared with physiological activators. All the bacterial isolates induced significant platelet activation, including integrin activation and alpha and dense-granule release, at levels equivalent to those induced by potent physiological platelet activators that induced stable aggregates. The ability to escape the aggregates and to resist the antibacterial effects of platelets was dependent on active protein synthesis by the bacteria within the aggregate. We conclude that S. pyogenes bacteria can temporarily cover themselves with activated platelets, and we propose that this may facilitate survival of the bacteria in the presence of platelets.

The M1 protein of Streptococcus pyogenes triggers an innate uptake mechanism into polarized human endothelial cells

Serotype M1 Streptococcus pyogenes is a major human pathogen associated with severe invasive diseases causing high morbidity and mortality. In a substantial number of cases, invasive disease develops in previously healthy individuals with no obvious port of entry. This has led to the hypothesis that the source of streptococci in these cases is a transient bacteraemia. This study focuses on the analysis of interaction of tissue-invasive serotype M1 S. pyogenes with human endothelial cells (EC) of the vascular system. We identify the M1 surface protein of S. pyogenes as the EC invasin which is recognised by polarized human blood EC, thereby triggering rapid, phagocytosis-like uptake of streptococci into polarized EC layers. Upon internalization, the M1 S. pyogenes serotype is incorporated into phagosomes which traffic via the endosomal/lysosomal pathway. However, some of the streptococci successfully evade this innate killing process and hereby mediate their escape into the cytoplasm of the host cell. The results of this study demonstrate that blood EC possess an efficient uptake mechanism for serotype M1 S. pyogenes. Despite efficient phagocytosis, streptococcal survival within EC constitutes one potential mechanism which favours intracellular persistence and thus facilitates continuous infection and dissemination from the primary side of infection into deep tissue.

Adult invasive and noninvasive infections due to Streptococcus dysgalactiae subsp. equisimilis in France from 2006 to 2010

We characterized 182 Streptococcus dysgalactiae subsp. equisimilis isolates and analyzed the epidemiological data on the corresponding infections. stG6, stG485, and stG6792 were the 3 most prevalent invasive emm types among the 27 different emm types recovered. High rates of antimicrobial resistance were observed for macrolides (26.4%) and tetracycline (34.6%).

Invasive group A streptococcal infection: an update on the epidemiology and orthopaedic management

Invasive group A streptococcus (iGAS) is the most common cause of monomicrobial necrotising fasciitis. Necrotising infections of the extremities may present directly to orthopaedic surgeons or by reference from another admitting specialty. Recent epidemiological data from the Health Protection Agency suggest an increasing incidence of iGAS infection in England. Almost 40% of those affected had no predisposing illnesses or risk factors, and the proportion of children presenting with infections has risen. These observations have prompted the Chief Medical Officer for the Central Alerting System in England to write to general practitioners and hospitals, highlighting the need for clinical vigilance, early diagnosis and rapid initiation of treatment in suspected cases. The purpose of this annotation is to summarise the recent epidemiological trends, describe the presenting features and outline the current investigations and treatment of this rare but life-threatening condition.

Spontaneous perforation of the cystic duct in streptococcal toxic shock syndrome: a case report

Introduction

Streptococcal toxic shock syndrome is a complication of group A streptococcal infection, most often originating from the skin. The syndrome is characterized by fever, hypotension and multiple organ failure. Mortality rate may be as high as 80%.

Case presentation

A 25-year-old man of Indian origin presented with abdominal complaints, rash and fever after an episode of pharyngitis. The patient was operated and a biliary peritonitis was found caused by perforation of the cystic duct in the absence of calculi. Cholecystectomy was performed, but after the operation, the patient's condition worsened and multi-organ failure developed. Group A streptococci were cultured in blood taken at admission and streptococcal toxic shock syndrome was diagnosed. Treatment consisted of antibiotics, corticosteroids, immunoglobulin and supportive treatment for haemodynamic, respiratory and renal failure.

Conclusion

This is a patient with streptococcal toxic shock syndrome complicated by spontaneous perforation of the cystic duct. Spontaneous perforation of the cystic duct is a rare finding, most often reported in children and secondary to anatomic defects. We found only one similar adult case in the literature. Perforation may be due to microthrombosis and ischaemia, and so be a part of the multi-organ failure often found in streptococcal toxic shock syndrome.

Outbreak of invasive group A streptococcal disease among children attending a day-care center

BACKGROUND

Most cases of invasive group A streptococcal (GAS) disease arise sporadically in the community, but outbreaks of severe invasive GAS infections have been reported in closed environments, such as military populations, family communities and hospitals. An outbreak of invasive GAS disease involving 3 cases of streptococcal toxic shock syndrome (TSS), one with a fatal course, occurred among children attending a day-care center located in Cantabria, Northern Spain.

OBJECTIVE

To determine the characteristics of GAS isolates obtained from the outbreak environment.

METHODS

GAS isolates obtained from children attending the same day-care facility, staff members, and family contacts were assayed for emm typing, pulse-field gel electrophoresis (PFGE), and toxin-gene content. One isolate obtained from the fatal case was also characterized by multilocus sequence typing. Antimicrobial susceptibility testing was done. Strains from patients unrelated to the outbreak were included for comparison.

RESULTS

All GAS isolates from children attending the day-care center, including those from streptococcal TSS cases, shared the same emm type 4, genomic pattern by PFGE (A) and toxin-gene profile. Neither the emm type nor the PFGE pattern or toxin gene profile of the outbreak-associated strains were encountered among GAS isolated from household or staff contacts.

CONCLUSIONS

A clone of GAS belonging to emm type 4 and characterized by a specific PFGE pattern and toxin-gene profile was responsible for a community outbreak of streptococcal TSS disease in a child day-care center in Spain. This is the first day-care outbreak reported in our country.

Antibiotic Prescribing in Critical Care: Specific Indications

This article outlines recommendations for the treatment of specific infections occurring in the setting of critical care. In the interests of brevity, a limited number of infections are discussed and recommendations are largely confined to empirical therapy. Basic principles of diagnosis and treatment apply in all cases, including appropriate de-escalation when an organism is identified. These aspects of treatment have been dealt with in part one of this article – ‘Antibiotic prescribing in critical care: general principles' published in the winter 2007 edition of JICS.

Severe streptococcal infection is associated with M protein-induced platelet activation and thrombus formation

Disturbed haemostasis is a central finding in severe Streptococcus pyogenes infection. In particular, microthrombi are found both at the local site of infection and at distant sites. Platelets are responsible for maintaining vascular function and haemostasis. We report here that M1 protein of S. pyogenes triggers immune-mediated platelet activation and thrombus formation. M1 protein is released from the bacterial surface and forms complexes with plasma fibrinogen. These complexes bind to the fibrinogen receptor on resting platelets. When these complexes also contain immunoglobulin G (IgG) against M1 protein, this will engage the Fc receptor on the platelets and activation will occur. Activation of the platelets leads to platelet aggregation and the generation of platelet-rich thrombi. Neutrophils and monocytes are in turn activated by the platelets. Platelet thrombi are deposited in the microvasculature, and aggregated platelets, IgG and M1 protein colocalize in biopsies from patients diagnosed with S. pyogenes toxic shock syndrome. This chain of events results in a pro-coagulant and pro-inflammatory state typical of severe S. pyogenes infection.

Deoxyribonucleoside kinases activate nucleoside antibiotics in severely pathogenic bacteria

Common bacterial pathogens are becoming progressively more resistant to traditional antibiotics, representing a major public-health crisis. Therefore, there is a need for a variety of antibiotics with alternative modes of action. In our study, several nucleoside analogs were tested against pathogenic staphylococci and streptococci. We show that pyrimidine-based nucleoside analogs, like 3'-azido-3'-deoxythymidine (AZT) and 2',2'-difluoro-2'deoxycytidine (gemcitabine), are specifically activated by the endogenous bacterial deoxyribonucleoside kinases, leading to cell death. Deoxyribonucleoside kinase-deficient Escherichia coli strains become highly susceptible to nucleoside analogs when they express recombinant kinases from Staphylococcus aureus or Streptococcus pyogenes. We further demonstrate that recombinant S. aureus deoxyadenosine kinase efficiently phosphorylates the anticancer drug gemcitabine in vitro and is therefore the key enzyme in the activation pathway. When adult mice were infected intraperitoneally with a fatal dose of S. pyogenes strain AP1 and afterwards received gemcitabine, they failed to develop a systemic infection. Nucleoside analogs may therefore represent a promising alternative for combating pathogenic bacteria.

Molecular epidemiologic comparison of 2 unusual clusters of group a streptococcal necrotizing fasciitis in Hawaii

Two clusters of necrotizing fasciitis (NF) due to group A streptococcus (GAS) were identified on the Hawaiian islands of Kauai and Maui during 1997 and 2002, respectively. The emm gene sequence types and the pulsed-field gel electrophoresis patterns were determined for 6 isolates recovered from patients with NF and for 116 isolates recovered from patients with temporally associated community-acquired GAS infection. No predominant emm type was identified, and the emm types of 64 (52.5%) of the isolates were considered to be uncommon in the continental United States. These findings suggest that unusual emm types might be responsible for invasive GAS infections in patients from Hawaii.

Necrotizing Soft Tissue Infections

Necrotizing soft tissue infections are characterized by necrosis of skin and associated structures. Despite advances in the diagnosis and treatment of these infections, the mortality remains high. There have been increasing reports of necrotizing fasciitis caused by group A Streptococcus over the past decade. Recent information supports the role of superantigens in the pathogenesis of this infection. The approach to management requires expeditious evaluation with early surgery and appropriate antimicrobial agents. Limited data suggest that surgical debridement may be delayed in selected patients until the patient is stable by the use of intravenous immunoglobulin, which can neutralize superantigens.

Generation of protective immunity by inactivated recombinant staphylococcal enterotoxin B vaccine in nonhuman primates and identification of correlates of immunity

At this time there are no vaccines or therapeutics to protect against staphylococcal enterotoxin B (SEB) exposure. Here, we report vaccine efficacy of an attenuated SEB in a nonhuman primate model following lethal aerosol challenge and identify several biomarkers of protective immunity. Initial in vitro results indicated that the mutation of key amino acid residues in the major histocompatibility complex (MHC) class II binding sites of SEB produced a nontoxic form of SEB, which had little to no detectable binding to MHC class II molecules, and lacked T-cell stimulatory activities. When examined in a mouse model, we found that the attenuated SEB retained antigenic structures and elicited protective immune responses against wild-type SEB challenge. Subsequently, a vaccine regimen against SEB in a nonhuman primate model was partially optimized, and investigations of immune biomarkers as indicators of protection were performed. SEB-naïve rhesus monkeys were vaccinated two or three times with 5 or 20 microg of the attenuated SEB and challenged by aerosol with wild-type SEB toxin. Unlike exposure to the native toxin, the vaccine did not trigger the release of inflammatory cytokines (TNF alpha, IL6, or IFN gamma). All rhesus monkeys that developed anti-SEB serum titers > or = 10(4) and elicited high levels of neutralizing antibody survived the aerosol challenge. These findings suggest that the attenuated SEB is fully protective against aerosolized toxin when administered to unprimed subjects. Moreover, experiments presented in this study identified various biomarkers that showed substantial promise as correlates of immunity and surrogate endpoints for assessing in vivo biological responses in primates, and possibly in humans, to vaccines against SEs.

drs (Distantly related sic) gene polymorphisms among emm12-type Streptococcus pyogenes isolates

Twenty-eight emm12-type Streptococcus pyogenes isolates from patients with invasive and noninvasive infections or from asymptomatic carriers were genetically typed. Sequencing of drs (distantly related sic [streptococcal inhibitor of complement]) genes identified two novel alleles and revealed a polymorphism for drs similar to that of sic. No association was observed between the five different drs alleles and the five restriction patterns of the vir regulon for the isolates studied. These data suggest that drs sequencing may be useful for further differentiation of S. pyogenes isolates with emm12 and identical vir regulon restriction patterns.

Fulminant liver failure in a child with invasive group A streptococcal infection

Liver involvement is mentioned in streptococcal toxic shock syndrome, but never as fulminant liver failure (FLF). We report the case of a 2-year-old child who developed isolated FLF secondary to invasive group A streptococcal infection without shock due to a M1T1-type strain expressing speA, speB and speC toxin genes. On antibiotics, he recovered rapidly without liver transplantation.

CONCLUSION

A streptococcal pyrogenic exotoxin likely constituted the initial insult leading to FLF. This etiology can be included in the differential diagnosis of FLF and would support early introduction of antibiotics.