Working towards a Group A Streptococcal vaccine: Report of a collaborative Trans-Tasman workshop

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.

Pilus proteins from Streptococcus pyogenes stimulate innate immune responses through Toll‐like receptor 2

The group A Streptococcus (GAS) pilus is a long, flexible, hair‐like structure anchored to the cell surface that facilitates the adherence of GAS to host cells, thus playing a critical role in initiating infections. Because of its important role in GAS virulence, the pilus has become an attractive target for vaccine development. While current research mainly focuses on pilus function and its potential as a vaccine component, there is a lack of knowledge on how the host immune system recognizes and responds to this abundant surface structure. Here we show that both assembled GAS pili and individual pilus proteins induce a potent release of the proinflammatory cytokines tumor necrosis factor and interleukin‐8. We further show that the surface‐exposed backbone pilin and ancillary pilin 1 subunits are Toll‐like receptor 2 (TLR2) agonists. Using reporter cell lines coexpressing human TLR2 in combination with either TLR1 or TLR6, we determined that activation was mediated by the TLR2/TLR6 heterodimer. Finally, we used solid‐phase and flow cytometry binding assays to illustrate a direct interaction between the pilus subunits and TLR2. These results provide further support for the suitability of the pilus as a vaccine component and opens potential avenues for using GAS pili as an adjuvant or immune‐modulation agent.

Update on group A streptococcal vaccine development

PURPOSE OF REVIEW

There is a global need for well tolerated, effective, and affordable vaccines to prevent group A streptococcal infections and their most serious complications. The aim of this review is to highlight the recent progress in the identification of promising vaccine antigens and new approaches to vaccine design that address the complexities of group A streptococcal pathogenesis and epidemiology.

RECENT FINDINGS

Combination vaccines containing multiple shared, cross-protective antigens have proven efficacious in mouse and nonhuman primate models of infection. The development of complex multivalent M protein-based vaccines is continuing and several have progressed through early-stage human clinical trials. Formulations of vaccines containing universal T-cell epitopes, toll-like receptor agonists, and other adjuvants more potent than alum have been shown to enhance protective immunogenicity. Although the group A streptococcal vaccine antigen landscape is populated with a number of potential candidates, the clinical development of vaccines has been impeded by a number of factors. There are now concerted global efforts to raise awareness about the need for group A streptococcal vaccines and to support progress toward eventual commercialization and licensure.

SUMMARY

Preclinical antigen discovery, vaccine formulation, and efficacy studies in animal models have progressed significantly in recent years. There is now a need to move promising candidates through the clinical development pathway to establish their efficacy in preventing group A streptococcal infections and their complications.

A multivalent T-antigen-based vaccine for Group A Streptococcus

Pili of Group A Streptococcus (GAS) are surface-exposed structures involved in adhesion and colonisation of the host during infection. The major protein component of the GAS pilus is the T-antigen, which multimerises to form the pilus shaft. There are currently no licenced vaccines against GAS infections and the T-antigen represents an attractive target for vaccination. We have generated a multivalent vaccine called TeeVax1, a recombinant protein that consists of a fusion of six T-antigen domains. Vaccination with TeeVax1 produces opsonophagocytic antibodies in rabbits and confers protective efficacy in mice against invasive disease. Two further recombinant proteins, TeeVax2 and TeeVax3 were constructed to cover 12 additional T-antigens. Combining TeeVax1–3 produced a robust antibody response in rabbits that was cross-reactive to a full panel of 21 T-antigens, expected to provide over 95% vaccine coverage. These results demonstrate the potential for a T-antigen-based vaccine to prevent GAS infections.

Immunogenicity Assessment of Cell Wall Carbohydrates of Group A Streptococcus via Self-Adjuvanted Glyco-lipopeptides

Identifying the immunogenic moieties and their precise structure of carbohydrates plays an important role for developing effective carbohydrate-based subunit vaccines. This study assessed the structure-immunogenicity relationship of carbohydrate moieties of a single repeating unit of group A carbohydrate (GAC) present on the cell wall of group A Streptococcus (GAS) using a rationally designed self-adjuvanted lipid-core peptide, instead of a carrier protein. Immunological evaluation of fully synthetic glyco-lipopeptides (particle size: 300-500 nm) revealed that construct consisting of higher rhamnose moieties (trirhamnosyl-lipopeptide) was able to induce enhanced immunogenic activity in mice, and GlcNAc moiety was not found to be an essential component of immunogenic GAC mimicked epitope. Trirhamnosyl-lipopeptide also showed 75-97% opsonic activity against four different clinical isolates of GAS and was comparable to a subunit peptide vaccine (J8-lipopeptide) which illustrated 65-96% opsonic activity.

Cellular chaining influences biofilm formation and structure in group A Streptococcus

Group A Streptococcal (GAS) biofilm formation is an important pathological feature contributing to the antibiotic tolerance and progression of various GAS infections. Although a number of bacterial factors have been described to promote in vitro GAS biofilm formation, the relevance of in vitro biofilms to host-associated biofilms requires further understanding. In this study, we demonstrate how constituents of the host environment, such as lysozyme and NaCl, can modulate GAS bacterial chain length and, in turn, shape GAS biofilm morphology and structure. Disruption of GAS chains with lysozyme results in biofilms that are more stable. Based on confocal microscopy, we attribute the increase in biofilm stability to a dense and compact three-dimensional structure produced by de-chained cells. To show that changes in biofilm stability and structure are due to the shortening of bacterial chains and not specific to the activity of lysozyme, we demonstrate that augmented chaining induced by NaCl or deletion of the autolysin gene mur1.2 produced defects in biofilm formation characterized by a loose biofilm architecture. We conclude that GAS biofilm formation can be directly influenced by host and environmental factors through the modulation of bacterial chain length, potentially contributing to persistence and colonization within the host. Further studies of in vitro biofilm models incorporating physiological constituents such as lysozyme may uncover new insights into the physiology of in vivo GAS biofilms.

Invasive group A Streptococcus disease in Australian children: 2016 to 2018 - a descriptive cohort study

Objectives

Invasive group A Streptococcus (iGAS) disease is serious and sometimes life-threatening. The Paediatric Active Enhanced Disease Surveillance (PAEDS) Network collects voluntary notifications from seven major Australian paediatric hospitals on patients with certain conditions, including iGAS disease. Our aims were to: 1) Describe the epidemiological distribution of paediatric iGAS disease in Australia and correlate this with influenza notifications, 2) Identify GAS strains commonly associated with invasive disease in children.

Methods

IGAS and influenza notification data were obtained (from the PAEDS Network and the Australian Institute of Health and Welfare, respectively, for the period 1 July 2016 to 30 June 2018). Included iGAS patients had GAS isolated from a normally sterile body site. Data were described according to selected clinical and demographic characteristics, including by age group and Australian State, with proportions and minimum incidence rates estimated.

Results

A total of 181 patients were identified, with most (115, 63.5%) <5 years old. The mean annual minimum incidence rate was 1.6 (95% confidence interval: 1.1–2.3) per 100,000 children across the study period. An epidemiological correlation with the seasonal burden of influenza was noted. Contact prophylaxis was not consistently offered. Of 96 patients with emm-typing results available, 72.9% showed emm-1, −4 or − 12.

Conclusions

Robust surveillance systems and cohesive patient management guidelines are needed. Making iGAS disease nationally notifiable would help facilitate this. Influenza vaccination may contribute to reducing seasonal increases in iGAS incidence. The burden of disease emphasises the need for ongoing progress in GAS vaccine development.

Group A, B, C, and G Streptococcus Lancefield antigen biosynthesis is initiated by a conserved α-d-GlcNAc-β-1,4-l-rhamnosyltransferase

Group A carbohydrate (GAC) is a bacterial peptidoglycan-anchored surface rhamnose polysaccharide (RhaPS) that is essential for growth of Streptococcus pyogenes and contributes to its ability to infect the human host. In this study, using molecular and synthetic biology approaches, biochemistry, radiolabeling techniques, and NMR and MS analyses, we examined the role of GacB, encoded in the S. pyogenes GAC gene cluster, in the GAC biosynthesis pathway. We demonstrate that GacB is the first characterized α-d-GlcNAc-β-1,4-l-rhamnosyltransferase that synthesizes the committed step in the biosynthesis of the GAC virulence determinant. Importantly, the substitution of S. pyogenes gacB with the homologous gene from Streptococcus agalactiae (Group B Streptococcus), Streptococcus equi subsp. zooepidemicus (Group C Streptococcus), Streptococcus dysgalactiae subsp. equisimilis (Group G Streptococcus), or Streptococcus mutans complemented the GAC biosynthesis pathway. These results, combined with those from extensive in silico studies, reveal a common phylogenetic origin of the genes required for this priming step in >40 pathogenic species of the Streptococcus genus, including members from the Lancefield Groups B, C, D, E, G, and H. Importantly, this priming step appears to be unique to streptococcal ABC transporter-dependent RhaPS biosynthesis, whereas the Wzx/Wzy-dependent streptococcal capsular polysaccharide pathways instead require an α-d-Glc-β-1,4-l-rhamnosyltransferase. The insights into the RhaPS priming step obtained here open the door to targeting the early steps of the group carbohydrate biosynthesis pathways in species of the Streptococcus genus of high clinical and veterinary importance.

Prospective Surveillance of Pediatric Invasive Group A Streptococcus Infection

BACKGROUND

Invasive group A Streptococcus (GAS) disease has an incidence in high-income countries of 3 to 5 per 100000 per annum and a case-fatality ratio of 10% to 15%. Although these rates are comparable to those of invasive meningococcal disease in Australia before vaccine introduction, invasive GAS disease currently requires reporting in only 2 jurisdictions.

METHODS

Data were collected prospectively through active surveillance at the Royal Children's Hospital, Melbourne (October 2014 to September 2016). Isolation of GAS from a sterile site was required for inclusion. Comprehensive demographic and clinical data were collected, and emm typing was performed on all isolates. Disease was considered severe if the patient required inotropic support or mechanical ventilation.

RESULTS

We recruited 28 patients. The median age of the patients was 3.5 years (range, 4 days to 11 years). Ten (36%) patients had severe disease. Fifteen (54%) children had presented to a medical practitioner for review in the 48 hours before their eventual admission, including 7 of the 10 patients with severe GAS infection. Complications 6 months after discharge persisted in 21% of the patients. emm1 was the most common emm type (29%).

CONCLUSION

We found considerable short- and longer-term morbidity associated with pediatric invasive GAS disease in our study. Disease manifestations were frequently severe, and more than one-third of the patients required cardiorespiratory support. More than one-half of the patients attended a medical practitioner for assessment but were discharged in the 48-hour period before admission, which suggests that there might have been a window for earlier diagnosis. Our methodology was easy to implement as a surveillance system.

Development of an opsonophagocytic killing assay for group a streptococcus

Group A Streptococcus (GAS) or Streptococcus pyogenes is responsible for an estimated 500,000 deaths worldwide each year. Protection against GAS infection is thought to be mediated by phagocytosis, enhanced by bacteria-specific antibody. There are no licenced GAS vaccines, despite many promising candidates in preclinical and early stage clinical development, the most advanced of which are based on the GAS M-protein. Vaccine progress has been hindered, in part, by the lack of a standardised functional assay suitable for vaccine evaluation. Current assays, developed over 50 years ago, rely on non-immune human whole blood as a source of neutrophils and complement. Variations in complement and neutrophil activity between donors result in variable data that is difficult to interpret. We have developed an opsonophagocytic killing assay (OPKA) for GAS that utilises dimethylformamide (DMF)-differentiated human promyelocytic leukemia cells (HL-60) as a source of neutrophils and baby rabbit complement, thus removing the major sources of variation in current assays. We have standardised the OPKA for several clinically relevant GAS strain types (emm1, emm6 and emm12) and have shown antibody-specific killing for each emm-type using M-protein specific rabbit antisera. Specificity was demonstrated by pre-incubation of the antisera with homologous M-protein antigens that blocked antibody-specific killing. Additional qualifications of the GAS OPKA, including the assessment of the accuracy, precision, linearity and the lower limit of quantification, were also performed. This GAS OPKA assay has the potential to provide a robust and reproducible platform to accelerate GAS vaccine development.

Molecular Epidemiology, Ecology, and Evolution of Group A Streptococci

The clinico-epidemiological features of diseases caused by group A streptococci (GAS) is presented through the lens of the ecology, population genetics, and evolution of the organism. The serological targets of three typing schemes (M, T, SOF) are themselves GAS cell surface proteins that have a myriad of virulence functions and a diverse array of structural forms. Horizontal gene transfer expands the GAS antigenic cell surface repertoire by generating numerous combinations of M, T, and SOF antigens. However, horizontal gene transfer of the serotype determinant genes is not unconstrained, and therein lies a genetic organization that may signify adaptations to a narrow ecological niche, such as the primary tissue reservoirs of the human host. Adaptations may be further shaped by selection pressures such as herd immunity. Understanding the molecular evolution of GAS on multiple levels-short, intermediate, and long term-sheds insight on mechanisms of host-pathogen interactions, the emergence and spread of new clones, rational vaccine design, and public health interventions.

Bivalent mucosal peptide vaccines administered using the LCP carrier system stimulate protective immune responses against Streptococcus pyogenes infection

Despite the broad knowledge about the pathogenicity of Streptococcus pyogenes there is still a controversy about the correlate of protection in GAS infections. We aimed in further improving the immune responses stimulated against GAS comparing different vaccine formulations including bis-(3',5')-cyclic dimeric adenosine monophosphate (c-di-AMP) and BPPCysMPEG, a derivative of the macrophage-activating lipopeptide (MALP-2), as adjuvants, respectively, to be administered with and without the universal T helper cell epitope P25 along with the optimized B cell epitope J14 of the M protein and B and T cell epitopes of SfbI. Lipopeptide based nano carrier systems (LCP) were used for efficient antigen delivery across the mucosal barrier. The stimulated immune responses were efficient in protecting mice against a respiratory challenge with a lethal dose of a heterologous S. pyogenes strain. Moreover, combination of the LCP based peptide vaccine with c-di-AMP allowed reduction of antigen dose at the same time maintaining vaccine efficacy.

Interventions for the prevention of recurrent erysipelas and cellulitis

BACKGROUND

Erysipelas and cellulitis (hereafter referred to as 'cellulitis') are common bacterial skin infections usually affecting the lower extremities. Despite their burden of morbidity, the evidence for different prevention strategies is unclear.

OBJECTIVES

To assess the beneficial and adverse effects of antibiotic prophylaxis or other prophylactic interventions for the prevention of recurrent episodes of cellulitis in adults aged over 16.

SEARCH METHODS

We searched the following databases up to June 2016: the Cochrane Skin Group Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, and LILACS. We also searched five trials registry databases, and checked reference lists of included studies and reviews for further references to relevant randomised controlled trials (RCTs). We searched two sets of dermatology conference proceedings, and BIOSIS Previews.

SELECTION CRITERIA

Randomised controlled trials evaluating any therapy for the prevention of recurrent cellulitis.

DATA COLLECTION AND ANALYSIS

Two authors independently carried out study selection, data extraction, assessment of risks of bias, and analyses. Our primary prespecified outcome was recurrence of cellulitis when on treatment and after treatment. Our secondary outcomes included incidence rate, time to next episode, hospitalisation, quality of life, development of resistance to antibiotics, adverse reactions and mortality.

MAIN RESULTS

We included six trials, with a total of 573 evaluable participants, who were aged on average between 50 and 70. There were few previous episodes of cellulitis in those recruited to the trials, ranging between one and four episodes per study.Five of the six included trials assessed prevention with antibiotics in participants with cellulitis of the legs, and one assessed selenium in participants with cellulitis of the arms. Among the studies assessing antibiotics, one study evaluated oral erythromycin (n = 32) and four studies assessed penicillin (n = 481). Treatment duration varied from six to 18 months, and two studies continued to follow up participants after discontinuation of prophylaxis, with a follow-up period of up to one and a half to two years. Four studies were single-centre, and two were multicentre; they were conducted in five countries: the UK, Sweden, Tunisia, Israel, and Austria.Based on five trials, antibiotic prophylaxis (at the end of the treatment phase ('on prophylaxis')) decreased the risk of cellulitis recurrence by 69%, compared to no treatment or placebo (risk ratio (RR) 0.31, 95% confidence interval (CI) 0.13 to 0.72; n = 513; P = 0.007), number needed to treat for an additional beneficial outcome (NNTB) six, (95% CI 5 to 15), and we rated the certainty of evidence for this outcome as moderate.Under prophylactic treatment and compared to no treatment or placebo, antibiotic prophylaxis reduced the incidence rate of cellulitis by 56% (RR 0.44, 95% CI 0.22 to 0.89; four studies; n = 473; P value = 0.02; moderate-certainty evidence) and significantly decreased the rate until the next episode of cellulitis (hazard ratio (HR) 0.51, 95% CI 0.34 to 0.78; three studies; n = 437; P = 0.002; moderate-certainty evidence).The protective effects of antibiotic did not last after prophylaxis had been stopped ('post-prophylaxis') for risk of cellulitis recurrence (RR 0.88, 95% CI 0.59 to 1.31; two studies; n = 287; P = 0.52), incidence rate of cellulitis (RR 0.94, 95% CI 0.65 to 1.36; two studies; n = 287; P = 0.74), and rate until next episode of cellulitis (HR 0.78, 95% CI 0.39 to 1.56; two studies; n = 287). Evidence was of low certainty.Effects are relevant mainly for people after at least two episodes of leg cellulitis occurring within a period up to three years.We found no significant differences in adverse effects or hospitalisation between antibiotic and no treatment or placebo; for adverse effects: RR 0.87, 95% CI 0.58 to 1.30; four studies; n = 469; P = 0.48; for hospitalisation: RR 0.77, 95% CI 0.37 to 1.57; three studies; n = 429; P = 0.47, with certainty of evidence rated low for these outcomes. The existing data did not allow us to fully explore its impact on length of hospital stay.The common adverse reactions were gastrointestinal symptoms, mainly nausea and diarrhoea; rash (severe cutaneous adverse reactions were not reported); and thrush. Three studies reported adverse effects that led to discontinuation of the assigned therapy. In one study (erythromycin), three participants reported abdominal pain and nausea, so their treatment was changed to penicillin. In another study, two participants treated with penicillin withdrew from treatment due to diarrhoea or nausea. In one study, around 10% of participants stopped treatment due to pain at the injection site (the active treatment group was given intramuscular injections of benzathine penicillin).None of the included studies assessed the development of antimicrobial resistance or quality-of-life measures.With regard to the risks of bias, two included studies were at low risk of bias and we judged three others as being at high risk of bias, mainly due to lack of blinding.

AUTHORS' CONCLUSIONS

In terms of recurrence, incidence, and time to next episode, antibiotic is probably an effective preventive treatment for recurrent cellulitis of the lower limbs in those under prophylactic treatment, compared with placebo or no treatment (moderate-certainty evidence). However, these preventive effects of antibiotics appear to diminish after they are discontinued (low-certainty evidence). Treatment with antibiotic does not trigger any serious adverse events, and those associated are minor, such as nausea and rash (low-certainty evidence). The evidence is limited to people with at least two past episodes of leg cellulitis within a time frame of up to three years, and none of the studies investigated other common interventions such as lymphoedema reduction methods or proper skin care. Larger, high-quality studies are warranted, including long-term follow-up and other prophylactic measures.

Development of a high-throughput opsonophagocytic assay for the determination of functional antibody activity against Streptococcus pyogenes using bioluminescence

The lack of standardised protocols for the assessment of functional antibodies has hindered Streptococcus pyogenes research and the development of vaccines. A robust, high throughput opsonophagocytic bactericidal assay to determine protective antibodies in human and rabbit serum has been developed that utilises bioluminescence as a rapid read out.

The Group A Streptococcus serotype M2 pilus plays a role in host cell adhesion and immune evasion

Group A Streptococcus (GAS), or Streptococcus pyogenes, is a human pathogen that causes diseases ranging from skin and soft tissue infections to severe invasive diseases, such as toxic shock syndrome. Each GAS strain carries a particular pilus type encoded in the variable fibronectin-binding, collagen-binding, T antigen (FCT) genomic region. Here, we describe the functional analysis of the serotype M2 pilus encoded in the FCT-6 region. We found that, in contrast to other investigated GAS pili, the ancillary pilin 1 lacks adhesive properties. Instead, the backbone pilin is important for host cell adhesion and binds several host factors, including fibronectin and fibrinogen. Using a panel of recombinant pilus proteins, GAS gene deletion mutants and Lactococcus lactis gain-of-function mutants we show that, unlike other GAS pili, the FCT-6 pilus also contributes to immune evasion. This was demonstrated by a delay in blood clotting, increased intracellular survival of the bacteria in macrophages, higher bacterial survival rates in human whole blood and greater virulence in a Galleria mellonella infection model in the presence of fully assembled FCT-6 pili.

Comparative M-protein analysis of Streptococcus pyogenes from pharyngitis and skin infections in New Zealand: Implications for vaccine development

Background

Acute rheumatic fever (ARF) and rheumatic heart disease (RHD) are responsible for a significant disease burden amongst Māori and Pacific populations in New Zealand (NZ). However, contemporary data are lacking regarding circulating group A Streptococcal (GAS) strains in NZ. Such information is important in guiding vaccine development.

Methods

GAS isolates from April to June 2015 were recovered from skin and pharyngeal samples from children living in areas of high social deprivation in Auckland, NZ, a significant proportion of which are Māori or Pacific. These children are among the highest risk group for developing ARF. Isolates were compared to concurrently collected pharyngeal isolates from Dunedin, NZ, where both the proportion of Māori and Pacific children and risk of developing ARF is low. Emm typing, emm cluster typing and theoretical coverage of the 30-valent vaccine candidate were undertaken as previously described.

Results

A high diversity of emm types and a high proportion of emm-pattern D and cluster D4 isolates were detected amongst both skin and pharyngeal isolates in children at high risk of ARF. Pharyngeal isolates from children at low risk of ARF within the same country were significantly less diverse, less likely to be emm pattern D, and more likely to be theoretically covered by the 30-valent M protein vaccine.

Conclusions

The high proportion of emm pattern D GAS strains amongst skin and pharyngeal isolates from children at high risk of ARF raises further questions about the role of skin infection in ARF pathogenesis. Emm types and emm clusters differed considerably between ARF endemic and non-endemic settings, even within the same country. This difference should be taken into account for vaccine development.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-016-1891-6) contains supplementary material, which is available to authorized users.

Impetigo and scabies - Disease burden and modern treatment strategies

Impetigo and scabies both present different challenges in resource-limited compared with industrialised settings. Severe complications of these skin infections are common in resource-limited settings, where the burden of disease is highest. The microbiology, risk factors for disease, diagnostic approaches and availability and suitability of therapies also vary according to setting. Taking this into account we aim to summarise recent data on the epidemiology of impetigo and scabies and describe the current evidence around approaches to individual and community based treatment.

Epidemiology of Invasive Group A Streptococcal Infections in the United States, 2005-2012

BACKGROUND

Invasive group A Streptococcus (GAS) infections are associated with significant morbidity and mortality rates. We report the epidemiology and trends of invasive GAS over 8 years of surveillance.

METHODS

From January 2005 through December 2012, we collected data from the Centers for Disease Control and Prevention's Active Bacterial Core surveillance, a population-based network of 10 geographically diverse US sites (2012 population, 32.8 million). We defined invasive GAS as isolation of GAS from a normally sterile site or from a wound in a patient with necrotizing fasciitis (NF) or streptococcal toxic shock syndrome (STSS). Available isolates were emm typed. We calculated rates and made age- and race-adjusted national projections using census data.

RESULTS

We identified 9557 cases (3.8 cases per 100 000 persons per year) with 1116 deaths (case-fatality rate, 11.7%). The case-fatality rates for septic shock, STSS, and NF were 45%, 38%, and 29%, respectively. The annual incidence was highest among persons aged ≥65 years (9.4/100 000) or <1 year (5.3) and among blacks (4.7/100 000). National rates remained steady over 8 years of surveillance. Factors independently associated with death included increasing age, residence in a nursing home, recent surgery, septic shock, NF, meningitis, isolated bacteremia, pneumonia, emm type 1 or 3, and underlying chronic illness or immunosuppression. An estimated 10 649-13 434 cases of invasive GAS infections occur in the United States annually, resulting in 1136-1607 deaths. In a 30-valent M-protein vaccine, emm types accounted for 91% of isolates.

CONCLUSIONS

The burden of invasive GAS infection in the United States remains substantial. Vaccines under development could have a considerable public health impact.

The Impact of Obesity and Diabetes on the Risk of Disease and Death due to Invasive Group A Streptococcus Infections in Adults

BACKGROUND

Invasive group A Streptococcus (iGAS) infections cause significant morbidity and mortality worldwide. We analyzed whether obesity and diabetes were associated with iGAS infections and worse outcomes among an adult US population.

METHODS

We determined the incidence of iGAS infections using 2010-2012 cases in adults aged ≥ 18 years from Active Bacterial Core surveillance (ABCs), a population-based surveillance system, as the numerator. For the denominator, we used ABCs catchment area population estimates from the 2011 to 2012 Behavioral Risk Factor Surveillance System (BRFSS) survey. The relative risk (RR) of iGAS was determined by obesity and diabetes status after adjusting for age group, gender, race, and other underlying conditions through binomial logistic regression. Multivariable logistic regression was used to determine whether obesity or diabetes was associated with increased odds of death due to iGAS compared to normal weight and nondiabetic patients, respectively.

RESULTS

Between 2010 and 2012, 2927 iGAS cases were identified. Diabetes was associated with an increased risk of iGAS in all racial groups (adjusted risk ratio [aRR] ranged from 2.71 to 5.08). Grade 3 obesity (body mass index [BMI] ≥ 40) was associated with an increased risk of iGAS for whites (aRR = 3.47; 95% confidence interval [CI], 3.00-4.01). Grades 1-2 (BMI = 30.0-<40.0) and grade 3 obesity were associated with an increased odds of death (odds ratio [OR] = 1.55, [95% CI, 1.05, 2.29] and OR = 1.62 [95% CI, 1.01, 2.61], respectively) when compared to normal weight patients.

CONCLUSIONS

These results may help target vaccines against GAS that are currently under development. Efforts to develop enhanced treatment regimens for iGAS may improve prognoses for obese patients.

Modification of the classical Lancefield assay of group A streptococcal killing to reduce inter-donor variation

The lack of a surrogate-of-immunity assay presents a major barrier to Streptococcus pyogenes research. Modification of the Lancefield assay to include an antibody digestion step reduced inter-donor variation and permitted detection of the anti-streptococcal activity of intravenous immunoglobulin and convalescent serum, thus facilitating retrospective evaluation of immunity using stored samples.

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The lack of a surrogate-of-immunity assay is a major barrier to S. pyogenes research.

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Pre-treatment of whole blood with IdeS standardised bacterial growth between donors.

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IdeS was subsequently inhibited using a non-cytotoxic iodoacetamide derivative.

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The bactericidal action of stored samples could then be measured by Lancefield assay.

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The modified assay facilitates retrospective dissection of anti-S. pyogenes immunity.

Validation of an automated colony counting system for group A Streptococcus

Background

The practice of counting bacterial colony forming units on agar plates has long been used as a method to estimate the concentration of live bacteria in culture. However, due to the laborious and potentially error prone nature of this measurement technique, an alternative method is desirable. Recent technologic advancements have facilitated the development of automated colony counting systems, which reduce errors introduced during the manual counting process and recording of information. An additional benefit is the significant reduction in time taken to analyse colony counting data. Whilst automated counting procedures have been validated for a number of microorganisms, the process has not been successful for all bacteria due to the requirement for a relatively high contrast between bacterial colonies and growth medium. The purpose of this study was to validate an automated counting system for use with group A Streptococcus (GAS).

Results

Methods: Twenty-one different GAS strains, representative of major emm-types, were selected for assessment. In order to introduce the required contrast for automated counting, 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) dye was added to Todd–Hewitt broth with yeast extract (THY) agar. Growth on THY agar with TTC was compared with growth on blood agar and THY agar to ensure the dye was not detrimental to bacterial growth. Automated colony counts using a ProtoCOL 3 instrument were compared with manual counting to confirm accuracy over the stages of the growth cycle (latent, mid-log and stationary phases) and in a number of different assays. The average percentage differences between plating and counting methods were analysed using the Bland–Altman method.

Conclusions

Results: A percentage difference of ±10 % was determined as the cut-off for a critical difference between plating and counting methods. All strains measured had an average difference of less than 10 % when plated on THY agar with TTC. This consistency was also observed over all phases of the growth cycle and when plated in blood following bactericidal assays. Agreement between these methods suggest the use of an automated colony counting technique for GAS will significantly reduce time spent counting bacteria to enable a more efficient and accurate measurement of bacteria concentration in culture.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-016-1875-z) contains supplementary material, which is available to authorized users.

Group A streptococcal strains isolated in Lao People's Democratic Republic from 2004 to 2013

Epidemiological data regarding group A streptococcal (GAS) infections in South East Asia are scarce with no information from Laos. We characterized emm types, emm clusters and the antibiotic resistance profile of 124 GAS isolates recovered in Laos during 2004-2013. Most strains were recovered from skin and invasive infections (76% and 19%, respectively). Thirty-four emm types were identified as belonging to 12 emm clusters and no novel emm types were identified. No significant differences were observed in the distribution of emm types or emm clusters according to age or site of recovery (skin or invasive infections). There was moderate strain diversity in this country but considerable differences in emm-type distribution between Laos, Thailand and Cambodia. Vaccine coverage was high for the J8 vaccine candidate. The theoretical coverage for the 30-valent vaccine candidate needs further investigation. Antibiotic resistance was moderate to erythromycin and chloramphenicol (8% and 7%, respectively) and low to ofloxacin (<1%).

Molecular Epidemiology of Group A Streptococcus Infections in Cambodian Children, 2007-2012

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Epidemiology Analysis of Streptococcus pyogenes in a Hospital in Southern Taiwan by Use of the Updated emm Cluster Typing System

emm typing is the most widely used molecular typing method for the human pathogen Streptococcus pyogenes (group A streptococcus [GAS]). emm typing is based on a small variable region of the emm gene; however, the emm cluster typing system defines GAS types according to the nearly complete sequence of the emm gene. Therefore, emm cluster typing is considered to provide more information regarding the functional and structural properties of M proteins in different emm types of GAS. In the present study, 677 isolates collected between 1994 and 2008 in a hospital in southern Taiwan were analyzed by the emm cluster typing system. emm clusters A-C4, E1, E6, and A-C3 were the most prevalent emm cluster types and accounted for 67.4% of total isolates. emm clusters A-C4 and E1 were associated with noninvasive diseases, whereas E6 was significantly associated with both invasive and noninvasive manifestations. In addition, emm clusters D4, E2, and E3 were significantly associated with invasive manifestations. Furthermore, we found that the functional properties of M protein, including low fibrinogen-binding and high IgG-binding activities, were correlated significantly with invasive manifestations. In summary, the present study provides updated epidemiological information on GAS emm cluster types in southern Taiwan.

M-Protein Analysis of Streptococcus pyogenes Isolates Associated with Acute Rheumatic Fever in New Zealand

We applied an emm cluster typing system to group A Streptococcus strains in New Zealand, including those associated with acute rheumatic fever (ARF). We observed few so-called rheumatogenic emm types but found a high proportion of emm types previously associated with pyoderma, further suggesting a role for skin infection in ARF.

Streptococcal pharyngitis in schoolchildren in Bamako, Mali

BACKGROUND

Group A streptococcus (GAS) pharyngitis is associated with high rates of rheumatic heart disease in developing countries. We sought to identify guidelines for empiric treatment of pharyngitis in low-resource settings. To inform the design of GAS vaccines, we determined the emm types associated with pharyngitis among African schoolchildren.

METHODS

Surveillance for pharyngitis was conducted among children 5-16 years of age attending schools in Bamako, Mali. Students were encouraged to visit a study clinician when they had a sore throat. Enrollees underwent evaluation and throat swab for isolation of GAS. Strains were emm typed by standard methods.

RESULTS

GAS was isolated from 449 (25.5%) of the 1,759 sore throat episodes. Painful cervical adenopathy was identified in 403 children (89.8%) with GAS infection and was absent in 369 uninfected children (28.2%). Emm type was determined in 396 (88.2%) of the 449 culture-positive children; 70 types were represented and 14 types accounted for 49% of isolates. Based on the proportion of the 449 isolates bearing emm types included in the 30-valent vaccine (31.0%) plus nonvaccine types previously shown to react to vaccine-induced bactericidal antibodies (44.1%), the vaccine could protect against almost 75% of GAS infections among Bamako schoolchildren.

CONCLUSIONS

Two promising strategies could reduce rheumatic heart disease in low-resource settings. Administering antibiotics to children with sore throat and tender cervical adenopathy could treat most GAS-positive children while reducing use of unnecessary antibiotics for uninfected children. Broad coverage against M types associated with pharyngitis in Bamako schoolchildren might be achieved with the 30-valent GAS vaccine under development.

Management of invasive group A streptococcal infections

Invasive group A streptococcal (GAS) disease in children includes deep soft tissue infection, bacteraemia, bacteraemic pneumonia, meningitis and osteomyelitis. The expression of toxins and super antigens by GAS can complicate infection by triggering an overwhelming systemic inflammatory response, referred to as streptococcal toxic shock syndrome (STSS). The onset and progression of GAS disease can be rapid, and the associated mortality high. Prompt antibiotics therapy and early surgical debridement of infected tissue are essential. Adjunctive therapy with intravenous immunoglobulin and hyperbaric therapy may improve outcomes in severe disease. Nosocomial outbreaks and secondary cases in close personal contacts are not uncommon; infection control measures and consideration of prophylactic antibiotics to those at high risk are important aspects of disease control. To reduce a substantial part of the global burden of GAS disease, an affordable GAS vaccine with efficacy against a broad number of strains is needed.

Survey of the bp/tee genes from clinical group A streptococcus isolates in New Zealand - implications for vaccine development

Group A streptococcus (GAS) is responsible for a wide range of diseases ranging from superficial infections, such as pharyngitis and impetigo, to life-threatening diseases, such as toxic shock syndrome and acute rheumatic fever (ARF). GAS pili are hair-like extensions protruding from the cell surface and consist of highly immunogenic structural proteins: the backbone pilin (BP) and one or two accessory pilins (AP1 and AP2). The protease-resistant BP builds the pilus shaft and has been recognized as the T-antigen, which forms the basis of a major serological typing scheme that is often used as a supplement to M typing. A previous sequence analysis of the bp gene (tee gene) in 39 GAS isolates revealed 15 different bp/tee types. In this study, we sequenced the bp/tee gene from 100 GAS isolates obtained from patients with pharyngitis, ARF or invasive disease in New Zealand. We found 20 new bp/tee alleles and four new bp/tee types/subtypes. No association between bp/tee type and clinical outcome was observed. We confirmed earlier reports that the emm type and tee type are associated strongly, but we also found exceptions, where multiple tee types could be found in certain M/emm type strains, such as M/emm89. We also reported, for the first time, the existence of a chimeric bp/tee allele, which was assigned into a new subclade (bp/tee3.1). A strong sequence conservation of the bp/tee gene was observed within the individual bp/tee types/subtypes (>97 % sequence identity), as well as between historical and contemporary New Zealand and international GAS strains. This temporal and geographical sequence stability provided further evidence for the potential use of the BP/T-antigen as a vaccine target.

Vaccination against the M protein of Streptococcus pyogenes prevents death after influenza virus: S. pyogenes super-infection

Influenza virus infections are associated with a significant number of illnesses and deaths on an annual basis. Many of the deaths are due to complications from secondary bacterial invaders, including Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae, and Streptococcus pyogenes. The β-hemolytic bacteria S. pyogenes colonizes both skin and respiratory surfaces, and frequently presents clinically as strep throat or impetigo. However, when these bacteria gain access to normally sterile sites, they can cause deadly diseases including sepsis, necrotizing fasciitis, and pneumonia. We previously developed a model of influenza virus:S. pyogenes super-infection, which we used to demonstrate that vaccination against influenza virus can limit deaths associated with a secondary bacterial infection, but this protection was not complete. In the current study, we evaluated the efficacy of a vaccine that targets the M protein of S. pyogenes to determine whether immunity toward the bacteria alone would allow the host to survive an influenza virus:S. pyogenes super-infection. Our data demonstrate that vaccination against the M protein induces IgG antibodies, in particular those of the IgG1 and IgG2a isotypes, and that these antibodies can interact with macrophages. Ultimately, this vaccine-induced immunity eliminated death within our influenza virus:S. pyogenes super-infection model, despite the fact that all M protein-vaccinated mice showed signs of illness following influenza virus inoculation. These findings identify immunity against bacteria as an important component of protection against influenza virus:bacteria super-infection.