emm and C-repeat region molecular typing of beta-hemolytic Streptococci in a tropical country: implications for vaccine development

Streptococcus dysgalactiae subsp. equisimilis infection and its intersection with Streptococcus pyogenes

SUMMARYStreptococcus dysgalactiae subsp. equisimilis (SDSE) is an increasingly recognized cause of disease in humans. Disease manifestations range from non-invasive superficial skin and soft tissue infections to life-threatening streptococcal toxic shock syndrome and necrotizing fasciitis. Invasive disease is usually associated with co-morbidities, immunosuppression, and advancing age. The crude incidence of invasive disease approaches that of the closely related pathogen, Streptococcus pyogenes. Genomic epidemiology using whole-genome sequencing has revealed important insights into global SDSE population dynamics including emerging lineages and spread of anti-microbial resistance. It has also complemented observations of overlapping pathobiology between SDSE and S. pyogenes, including shared virulence factors and mobile gene content, potentially underlying shared pathogen phenotypes. This review provides an overview of the clinical and genomic epidemiology, disease manifestations, treatment, and virulence determinants of human infections with SDSE with a particular focus on its overlap with S. pyogenes. In doing so, we highlight the importance of understanding the overlap of SDSE and S. pyogenes to inform surveillance and disease control strategies.

Inter-species gene flow drives ongoing evolution of Streptococcus pyogenes and Streptococcus dysgalactiae subsp. equisimilis

Streptococcus dysgalactiae subsp. equisimilis (SDSE) is an emerging cause of human infection with invasive disease incidence and clinical manifestations comparable to the closely related species, Streptococcus pyogenes. Through systematic genomic analyses of 501 disseminated SDSE strains, we demonstrate extensive overlap between the genomes of SDSE and S. pyogenes. More than 75% of core genes are shared between the two species with one third demonstrating evidence of cross-species recombination. Twenty-five percent of mobile genetic element (MGE) clusters and 16 of 55 SDSE MGE insertion regions were shared across species. Assessing potential cross-protection from leading S. pyogenes vaccine candidates on SDSE, 12/34 preclinical vaccine antigen genes were shown to be present in >99% of isolates of both species. Relevant to possible vaccine evasion, six vaccine candidate genes demonstrated evidence of inter-species recombination. These findings demonstrate previously unappreciated levels of genomic overlap between these closely related pathogens with implications for streptococcal pathobiology, disease surveillance and prevention.

Group A Streptococcus Infections: Their Mechanisms, Epidemiology, and Current Scope of Vaccines

Group A streptococci (GAS) are gram-positive, cocci-shaped bacteria that cause a wide variety of infections and are a cause of significant health burden, particularly in lower- and middle-income nations. The GAS genome contains a number of virulence factors such as the M-protein, hyaluronic acid, C5a peptidase, etc. Despite its significant health burden across the globe, a proper vaccine against GAS infections is not yet available. Various candidates for an effective GAS vaccine are currently being researched. These are based on various parts of the streptococcal genome. These include candidates based on the N-terminal region of the M protein, the conserved C-terminal region of the M protein, and other parts of the streptococcal genome. The development of a vaccine against GAS infections is hampered by certain challenges, such as extensive genetic heterogeneity and high protein sequence variation. This review paper sheds light on the various virulence factors of GAS, their epidemiology, the different vaccine candidates currently being researched, and the challenges associated with M-protein and non-M-protein-based vaccines. This review also sheds light on the current scenario regarding the status of vaccine development against GAS-related infections.

M-protein based vaccine induces immunogenicity and protection from Streptococcus pyogenes when delivered on a high-density microarray patch (HD-MAP)

We evaluated vaccination against Streptococcus pyogenes with the candidate vaccine, J8-DT, delivered by a high-density microarray patch (HD-MAP). We showed that vaccination with J8-DT eluted from a coated HD-MAP (J8-DT/HD-MAP), induced similar total IgG responses to that generated by vaccination with J8-DT adjuvanted with Alum (J8-DT/Alum). We evaluated the effect of dose reduction and the number of vaccinations on the antibody response profile of vaccinated mice. A reduction in the number of vaccinations (from three to two) with J8-DT/HD-MAP induced comparable antibody responses to three vaccinations with intramuscular J8-DT/Alum. Vaccine-induced protection against an S. pyogenes skin challenge was assessed. J8-DT/HD-MAP vaccination led to a significant reduction in the number of S. pyogenes colony forming units in skin (92.9%) and blood (100%) compared to intramuscular vaccination with unadjuvanted J8-DT. The protection profile was comparable to that of intramuscular J8-DT/Alum. J8-DT/HD-MAP induced a shift in the antibody isotype profile, with a bias towards Th1-related isotypes, compared to J8-DT/Alum (Th2 bias). Based on the results of this study, the use of J8-DT/HD-MAP should be considered in future clinical development and control programs against S. pyogenes. Furthermore, the innate characteristics of the technology, such as vaccine stability and increased coverage, ease of use, reduction of sharp waste and the potential reduction of dose may be advantageous compared to current vaccination methods.

Randomized Trial of Community Treatment With Azithromycin and Ivermectin Mass Drug Administration for Control of Scabies and Impetigo

Background

Scabies is a public health problem in many countries, with impetigo and its complications important consequences. Ivermectin based mass drug administration (MDA) reduces the prevalence of scabies and, to a lesser extent, impetigo. We studied the impact of co-administering azithromycin on the prevalence of impetigo and antimicrobial resistance.

Methods

Six communities were randomized to receive either ivermectin-based MDA or ivermectin-based MDA co-administered with azithromycin. We measured scabies and impetigo prevalence at baseline and 12 months. We collected impetigo lesions swabs at baseline, 3 and 12 months to detect antimicrobial resistance.

Results

At baseline, scabies and impetigo prevalences were 11.8% and 10.1% in the ivermectin-only arm and 9.2% and 12.1% in the combined treatment arm. At 12 months, the prevalences had fallen to 1.0% and 2.5% in the ivermectin-only arm and 0.7% and 3.3% in the combined treatment arm. The proportion of impetigo lesions containing Staphylococcus aureus detected did not change (80% at baseline vs 86% at 12 months; no significant difference between arms) but the proportion containing pyogenic streptococci fell significantly (63% vs 23%, P < .01). At 3 months, 53% (8/15) of S. aureus isolates were macrolide-resistant in the combined treatment arm, but no resistant strains (0/13) were detected at 12 months.

Conclusions

Co-administration of azithromycin with ivermectin led to similar decreases in scabies and impetigo prevalence compared to ivermectin alone. The proportion of impetigo lesions containing pyogenic streptococci declined following MDA. There was a transient increase in the proportion of macrolide-resistant S. aureus strains following azithromycin MDA.

Clinical Trials Registration

clinicaltrials.gov (NCT02775617).

Semisynthetic, self-adjuvanting vaccine development: Efficient, site-specific sortase A-mediated conjugation of Toll-like receptor 2 ligand FSL-1 to recombinant protein antigens under native conditions and application to a model group A streptococcal vaccine

Protein antigens are, in general, weakly immunogenic, and therefore require co-delivery with adjuvants to stimulate potent immune responses. The fusion of (poly)peptide antigens to immunostimulatory adjuvants (e.g. Toll-like receptor (TLR) agonists) has been demonstrated to greatly improve vaccine potency compared to mixtures of antigen and adjuvant. Chemical approaches, to enable the rapid, site-specific and high-yielding linkage of TLR2 ligands to recombinant protein antigens, have been previously optimized. These approaches require the use of denaturing conditions to ensure high reaction yields, which limits their application, as maintenance of native protein folding is necessary to elicit antibodies against conformational epitopes. Here, this work aimed to optimize an alternative method, to ensure the efficient bioconjugation of TLR2 ligands onto folded protein antigens. An enzyme-mediated approach, using Staphylococcus aureus sortase A (or a penta mutant with enhanced efficiency), was optimized for reaction yield and time, as well as enzyme type and amount. This approach enabled the site-specific conjugation of the TLR2-agonist fibroblast-stimulating lipopeptide-1 (FSL-1) onto a model group A Streptococcus (GAS) recombinant polytope antigen under conditions that maintain protein folding, yielding a homogeneous, molecularly-defined product, with ligation yields as high as 90%. Following intramuscular (IM) administration of the ligation product to humanized plasminogen AlbPLG1 mice, high-titer, antigen-specific IgG antibodies were observed, which conferred protection against subcutaneous challenge with GAS strain 5448. In comparison, mixtures of the GAS antigen with aluminum hydroxide or FSL-1 failed to provide protection, with the FSL-1 mixture yielding ~1000-fold lower antigen-specific IgG antibody titers, and the mixture with alum yielding a Th2-biased response compared to the more balanced Th1/Th2 responses observed with the FSL-1 conjugate. Overall, a FSL-1 bioconjugation method for the efficient production of antigen-TLR2 agonist conjugates, which maintain protein folding, was produced, with broad utility for the development of self-adjuvanting vaccines against subunit protein antigens.

Antibodies to the conserved region of the M protein and a streptococcal superantigen cooperatively resolve toxic shock-like syndrome in HLA-humanized mice

Invasive streptococcal disease (ISD) and toxic shock syndrome (STSS) result in over 160,000 deaths each year. We modelled these in HLA-transgenic mice infected with a clinically lethal isolate expressing Streptococcal pyrogenic exotoxin (Spe) C and demonstrate that both SpeC and streptococcal M protein, acting cooperatively, are required for disease. Vaccination with a conserved M protein peptide, J8, protects against STSS by causing a dramatic reduction in bacterial burden associated with the absence of SpeC and inflammatory cytokines in the blood. Furthermore, passive immunotherapy with antibodies to J8 quickly resolves established disease by clearing the infection and ablating the inflammatory activity of the M protein, which is further enhanced by addition of SpeC antibodies. Analysis of 77 recent isolates of Streptococcus pyogenes causing ISD, demonstrated that anti-J8 antibodies theoretically recognize at least 73, providing strong support for using antibodies to J8, with or without antibodies to SpeC, as a therapeutic approach.

Group A Streptococcus infections in children: from virulence to clinical management

PURPOSE OF REVIEW

Recent findings have open new perspectives on group A Streptococcus (GAS) virulence understanding with special focus on the carrier stage and new hopes for an efficient vaccine against this important pathogen.

RECENT FINDINGS

Understanding of carriage state, transmission and role of virulence factors in invasive infections have been recently active research fields questioning the link between carriage and infections and highlighting the potential to prevent invasive diseases. New roles for already well known virulence factors, such as Streptolysin O, M protein or NAD(+)-glycohydrolase have been discovered. Immunological studies have also shown diversity in both clinical and immunological responses toward various GAS antigens raising questions, and hopes, for the development of an efficient global vaccine candidate.

SUMMARY

A greater understanding of GAS virulence strategies, and their associated clinical manifestations, may be obtained by shifting our research scope toward virulence determinant interactions and cooperation rather than focusing on individual virulence factor or specific strain characterization only.

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.

Immune Cross-Opsonization Within emm Clusters Following Group A Streptococcus Skin Infection: Broadening the Scope of Type-Specific Immunity

Background

Group AStreptococcus (GAS) skin infections are particularly prevalent in developing nations. The GAS M protein, by which strains are differentiated into >220 differentemm types, is immunogenic and elicits protective antibodies. A major obstacle for vaccine development has been the traditional understanding that immunity following infection is restricted to a singleemm type. However, recent evidence has led to the hypothesis of immune cross-reactivity betweenemm types.

Methods

We investigated the human serological response to GAS impetigo in Fijian schoolchildren, focusing on 3 majoremm clusters (E4, E6, and D4). Pre- and postinfection sera were assayed by enzyme-linked immunosorbent assay with N-terminal M peptides and bactericidal assays using the infecting-type strain,emm cluster–related strains, and nonrelated strains.

Results

Twenty of the 53 paired sera demonstrated a ≥4-fold increase in antibody titer against the infecting type. When tested against all cluster-related M peptides, we found that 9 of 17 (53%) paired sera had a ≥4-fold increase in antibody titer to cluster-related strains as well. When grouped by cluster, the mean change to cluster-relatedemm types in E4 and E6 was >4-fold (5.9-fold and 19.5-fold, respectively) but for D4 was 3.8-fold. The 17 paired sera were tested in bactericidal assays against selected cluster-related and nonrelated strains. While the responses were highly variable, numerous instances of cross-reactive killing were observed.

Conclusions

These data demonstrate that M type–specific and cross-reactive immune responses occur following skin infection. The cross-reactive immune responses frequently align withemm clusters, raising new opportunities to design multivalent vaccines with broad coverage.

Physicochemical characterisation, immunogenicity and protective efficacy of a lead streptococcal vaccine: progress towards Phase I trial

Globally, group A streptococcal infections are responsible for over 500,000 deaths per year. A safe vaccine that does not induce autoimmune pathology and that affords coverage for most GAS serotypes is highly desired. We have previously demonstrated that a vaccine based on the conserved M-protein epitope, J8 was safe and immunogenic in a pilot Phase I study. We subsequently improved vaccine efficacy by incorporation of a B-cell epitope from the IL-8 protease, SpyCEP, which protected IL-8 and enhanced neutrophil ingress to the site of infection. We have now substituted the carrier protein, diphtheria toxoid with its superior analogue, CRM197 which provides better immunogenicity and is widely used in licenced human vaccines. The new vaccine was compared with the DT conjugate vaccine to confirm that these modifications have not altered the physicochemical properties of the vaccine. This vaccine, when tested in an animal model of GAS infection, demonstrated significant reduction in systemic and local GAS burden, with comparable efficacy to the DT conjugate vaccine. The vaccine was shown to be equally effective in the presence of human plasma and in the presence of pre-existing DT-specific antibodies, thus minimising concerns regarding its potential efficacy in humans.

Sequence element enrichment analysis to determine the genetic basis of bacterial phenotypes

Bacterial genomes vary extensively in terms of both gene content and gene sequence. This plasticity hampers the use of traditional SNP-based methods for identifying all genetic associations with phenotypic variation. Here we introduce a computationally scalable and widely applicable statistical method (SEER) for the identification of sequence elements that are significantly enriched in a phenotype of interest. SEER is applicable to tens of thousands of genomes by counting variable-length k-mers using a distributed string-mining algorithm. Robust options are provided for association analysis that also correct for the clonal population structure of bacteria. Using large collections of genomes of the major human pathogens Streptococcus pneumoniae and Streptococcus pyogenes, SEER identifies relevant previously characterized resistance determinants for several antibiotics and discovers potential novel factors related to the invasiveness of S. pyogenes. We thus demonstrate that our method can answer important biologically and medically relevant questions.

Plasticity and clonal population structure in bacterial genomes can hinder traditional SNP-based genetic association studies. Here, Corander and colleagues present a method to identify variable-length sequence elements enriched in a phenotype of interest, and demonstrate its use in human pathogens.

Repeat exposure to group A streptococcal M protein exacerbates cardiac damage in a rat model of rheumatic heart disease

Rheumatic fever and rheumatic heart disease (RF/RHD) develop following repeated infection with group A streptococci (GAS). We used the Rat Autoimmune Valvulitis (RAV) model of RF/RHD to demonstrate that repetitive booster immunization with GAS-derived recombinant M protein (rM5) resulted in an enhanced anti-cardiac myosin antibody response that may contribute to the breaking of immune tolerance leading to RF/RHD and increased infiltration of heart valves by mononuclear cells. With each boost, more inflammatory cells were observed infiltrating heart tissue which could lead to severe cardiac damage. We also found evidence that both complement and anti-M protein antibodies in serum from rM5-immunized rats have the potential to contribute to inflammation in heart valves by activating cardiac endothelium. More importantly, we have demonstrated by electrocardiography for the first time in the RAV model that elongation of P-R interval follows repetitive boost with rM5. Our observations provide experimental evidence for cardiac alterations following repeated exposure to GAS M protein with immunological and electrophysiological features resembling that seen in humans following recurrent GAS infection.

Accelerating the development of a group A Streptococcus vaccine: an urgent public health need

Group A Streptococcus (GAS) infections cause substantial worldwide morbidity and mortality, mostly associated with suppurative complications such as pharyngitis, impetigo, and non-suppurative immune syndromes such as acute rheumatic fever, rheumatic heart disease, and acute post-streptococcal glomerulonephritis. Deaths occur mostly in children, adolescents, and young adults in particular pregnant women in low- and middle-income countries. GAS strains are highly variable, and a GAS vaccine would need to overcome the issue of multiple strains. Several approaches have been used multivalent vaccines using N-terminal polypeptides of different M protein; conserved M protein vaccines with antigens from the conserved C-repeat portion of the M protein; incorporation selected T- and B-cell epitopes from the C-repeat region in a synthetic polypeptide or shorter single minimal B-cell epitopes from this same region; and non-M protein approaches utilizing highly conserved motives of streptococcal C5a peptidase, GAS carbohydrate and streptococcal fibronectin-binding proteins. A GAS vaccine represents urgent need for this neglected disease and should therefore deserve the greatest attention of international organizations, donors, and vaccine manufacturers.

Whole genome sequencing reveals extensive community-level transmission of group A Streptococcus in remote communities

Impetigo is common in remote Indigenous children of northern Australia, with the primary driver in this context being Streptococcus pyogenes [or group A Streptococcus (GAS)]. To reduce the high burden of impetigo, the transmission dynamics of GAS must be more clearly elucidated. We performed whole genome sequencing on 31 GAS isolates collected in a single community from children in 11 households with ⩾2 GAS-infected children. We aimed to determine whether transmission was occurring principally within households or across the community. The 31 isolates were represented by nine multilocus sequence types and isolates within each sequence type differed from one another by only 0-3 single nucleotide polymorphisms. There was evidence of extensive transmission both within households and across the community. Our findings suggest that strategies to reduce the burden of impetigo in this setting will need to extend beyond individual households, and incorporate multi-faceted, community-wide approaches.

Predicted Coverage and Immuno-Safety of a Recombinant C-Repeat Region Based Streptococcus pyogenes Vaccine Candidate

The C-terminal region of the M-protein of Streptococcus pyogenes is a major target for vaccine development. The major feature is the C-repeat region, consisting of 35–42 amino acid repeat units that display high but not perfect identity. SV1 is a S. pyogenes vaccine candidate that incorporates five 14mer amino acid sequences (called J14_i variants) from differing C-repeat units in a single recombinant construct. Here we show that the J14_i variants chosen for inclusion in SV1 are the most common variants in a dataset of 176 unique M-proteins. Murine antibodies raised against SV1 were shown to bind to each of the J14_i variants present in SV1, as well as variants not present in the vaccine. Antibodies raised to the individual J14_i variants were also shown to bind to multiple but different combinations of J14_i variants, supporting the underlying rationale for the design of SV1. A Lewis Rat Model of valvulitis was then used to assess the capacity of SV1 to induce deleterious immune response associated with rheumatic heart disease. In this model, both SV1 and the M5 positive control protein were immunogenic. Neither of these antibodies were cross-reactive with cardiac myosin or collagen. Splenic T cells from SV1/CFA and SV1/alum immunized rats did not proliferate in response to cardiac myosin or collagen. Subsequent histological examination of heart tissue showed that 4 of 5 mice from the M5/CFA group had valvulitis and inflammatory cell infiltration into valvular tissue, whereas mice immunised with SV1/CFA, SV1/alum showed no sign of valvulitis. These results suggest that SV1 is a safe vaccine candidate that will elicit antibodies that recognise the vast majority of circulating GAS M-types.

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.

Molecular epidemiology and genomics of group A Streptococcus

Streptococcus pyogenes (group A Streptococcus; GAS) is a strict human pathogen with a very high prevalence worldwide. This review highlights the genetic organization of the species and the important ecological considerations that impact its evolution. Recent advances are presented on the topics of molecular epidemiology, population biology, molecular basis for genetic change, genome structure and genetic flux, phylogenomics and closely related streptococcal species, and the long- and short-term evolution of GAS. The application of whole genome sequence data to addressing key biological questions is discussed.

Streptococcus pyogenes emm Types and Clusters during a 7-Year Period (2007 to 2013) in Pharyngeal and Nonpharyngeal Pediatric Isolates

Group A streptococcus (GAS) is an important cause of morbidity and mortality worldwide. Surveillance of emm types has important implications, as it can provide baseline information for possible implementation of vaccination. A total of 1,349 GAS pediatric isolates were collected during a 7-year period (2007 to 2013); emm typing was completed for 1,282 pharyngeal (84%) or nonpharyngeal (16%) isolates, and emm clusters and temporal changes were analyzed. Thirty-five different emm types, including 14 subtypes, were identified. The most prevalent emm types identified were 1 (16.7%), 12 (13.6%), 77 (10.9%), 4 (10.8%), 28 (10.4%), 6 (6.8%), 3 (6.6%), and 89 (6.6%), accounting for 82.3% of total isolates. Rheumatogenic emm types comprised 16.3% of total isolates. The emm types 12, 4, and 77 were more prevalent among pharyngeal isolates, and the emm types 1, 89, 6, 75, and 11 were more prevalent among nonpharyngeal isolates. The emm types identified belonged to 13 emm clusters, and the 8 most prevalent clusters comprised 97% of all isolates. There were statistically significant decreases in the prevalence of emm types 12, 4, 5, and 61 and increases in the prevalence of emm types 89, 75, and 11, compared with the period 2001 to 2006. The proposed 30-valent GAS vaccine, which is currently in preclinical studies, encompasses 97.2% of the emm types detected in our study and 97.4% of the erythromycin-resistant strains. In addition, it includes 93.3% of the emm types involved in bacteremia. A much greater diversity of GAS emm types was identified in our area than described previously. Seasonal fluctuations and the introduction of new emm types were observed. Continuous surveillance of emm types is needed in order to evaluate the possible benefits of an M protein-based GAS vaccine.

Geoepidemiological hints about Streptococcus pyogenes strains in relationship with acute rheumatic fever

Group A Streptococcus (GAS) strains are lately classified on the basis of sequence variations in the emm gene encoding the M protein, but despite the high number of distinct emm genotypes, the spectrum of phenotypes varying from invasive suppurative to non-suppurative GAS-related disorders has still to be defined. The relationship of GAS types with the uprising of acute rheumatic fever (ARF), a multisystemic disease caused by misdirected anti-GAS response in predisposed people, is also obscure. Studies published over the last 15 years were retrieved from PubMed using the keywords: "Streptococcus pyogenes" or "group A Streptococcus" and "acute rheumatic fever": the prevalence of peculiar emm types across different countries of the world is highly variable, depending on research designs, year of observation, country involved, patients' age, and gender. Most studies revealed that a relatively small number of specific emm/M protein types can be considered "rheumatogenic", as potentially characterized by the possibility of inducing ARF, with remarkable differences between developing and developed countries. The association between emm types and post-streptococcal manifestations is challenging, however surveillance of disease-causing variants in a specific community with high rate of ARF should be reinforced with the final goal of developing a potential primary prophylaxis against GAS infections.

Immune response against M protein-conserved region peptides from prevalent group A Streptococcus in a North Indian population

BACKGROUND

Group A streptococci (GAS) cause infections with a high prevalence in most developing countries. A GAS vaccine under trial that is based on the amino-terminus of the M protein provides type-specific immunity, and hence seems ineffective in India because of heterogeneous emm types. However, the conserved C-terminal region of the M protein protects against multiple serotypes. In this paper, the immune response generated against the conserved C-repeat region of the M protein was checked in an Indian population to establish their vaccine candidature.

METHODS

When screened for GAS, patients with pharyngitis, rheumatic fever/rheumatic heart disease (RF/RHD), and invasive disease showed heterogeneous emm types, out of which five prevalent types (1-2, 11, 49, 75 and 112) were selected for the study. The C-terminal region of their M proteins showed conserved C1-, C2-, and C3-repeats. The C1-repeat was more diverse and had two different J14-like sequences. Peptides to these C-terminal regions (J14.1 and J14-R6) were designed. Antibodies against these peptides were analyzed using the sera of 130 GAS-infected volunteers.

RESULTS

Serum antibodies were significantly higher in patients with acute rheumatic fever, RHD, and invasive disease than in patients with pharyngitis or the healthy controls. The serum antibodies to these peptides was higher in teenagers and adults than in children.

CONCLUSION

Results showed an association between streptococcal disease progression and the age-related development of immunity to the conserved regions. Hence, these peptides could be considered protective in impeding streptococcal infections worldwide.

The emm-cluster typing system for Group A Streptococcus identifies epidemiologic similarities across the Pacific region

BACKGROUND

Group A Streptococcus (GAS)-related disease is responsible for high mortality and morbidity in the Pacific region. The high diversity of circulating strains in this region has hindered vaccine development due to apparently low vaccine coverage of type-specific vaccines.

METHOD

Prospective passive surveillance of all GAS isolates in New Caledonia was undertaken in 2012 using emm typing and emm-cluster typing. Molecular data were compared with the results from a prior study undertaken in the same country and with data from 2 other Pacific countries, Fiji and Australia.

RESULTS

A high incidence of invasive infection was demonstrated at 43 cases per 100 000 inhabitants (95% confidence interval, 35-52 cases per 100 000 inhabitants). Three hundred eighteen GAS isolates belonging to 47 different emm types were collected. In Noumea, only 30% of the isolates recovered in 2012 belonged to an emm type that was present in the same city in 2006, whereas 69% of the isolates collected in 2012 belonged to an emm cluster present in 2006. When comparing New Caledonian, Australian, and Fijian data, very few common emm types were found, but 79%-86% of the isolates from each country belonged to an emm cluster present in all 3 countries. A vaccine that could protect against the 10 most frequent emm clusters in the Pacific region would potentially provide coverage ranging from 83% to 92%.

CONCLUSIONS

This study confirms the high disease burden of GAS infection in New Caledonia and supports the added value of the emm-cluster typing system to analyze GAS epidemiology and to help inform global GAS vaccine formulation.

Strategies in the development of vaccines to prevent infections with group A streptococcus

There has long been interest and demand for the development of a vaccine to prevent infections caused by the Gram-positive organism group A streptococcus. Despite numerous efforts utilizing advanced approaches such as genomics, proteomics and bio-informatics, there is currently no vaccine. Here we review various strategies employed to achieve this goal. We also discuss the approach that we have pursued, a non-host reactive, conformationally constrained minimal B cell epitope from within the C-repeat region of M-protein, and the potential limitations in moving forward.

Updated model of group A Streptococcus M proteins based on a comprehensive worldwide study

Group A Streptococcus (GAS) M protein is an important virulence factor and potential vaccine antigen, and constitutes the basis for strain typing (emm-typing). Although >200 emm-types are characterized, structural data were obtained from only a limited number of emm-types. We aim to evaluate the sequence diversity of near-full-length M proteins from worldwide sources and analyse their structure, sequence conservation and classification. GAS isolates recovered from throughout the world during the last two decades underwent emm-typing and complete emm gene sequencing. Predicted amino acid sequence analyses, secondary structure predictions and vaccine epitope mapping were performed using MUSCLE and Geneious software. A total of 1086 isolates from 31 countries were analysed, representing 175 emm-types. emm-type is predictive of the whole protein structure, independent of geographical origin or clinical association. Findings of an emm-type paired with multiple, highly divergent central regions were not observed. M protein sequence length, the presence or absence of sequence repeats and predicted secondary structure were assessed in the context of the latest vaccine developments. Based on these global data, the M6 protein model is updated to a three representative M protein (M5, M80 and M77) model, to aid in epidemiological analysis, vaccine development and M protein-related pathogenesis studies.

In Vivo Efficacy of a Chimeric Peptide Derived from the Conserved Region of the M Protein against Group C and G Streptococci

The J8 peptide from the conserved region of the M protein protects against group A streptococcus infections. In this study, we demonstrate that vaccination with a J8-containing formulation induces IgG that recognizes and binds group C and G streptococci. Moreover, this formulation has the potential to provide protection against infections caused by these organisms.

Identification and cluster analysis of Streptococcus pyogenes by MALDI-TOF mass spectrometry

Background

Whole-cell matrix–assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) has been successfully applied for bacterial identification and typing of many pathogens. The fast and reliable qualities of MALDI-TOF MS make it suitable for clinical diagnostics. MALDI-TOF MS for the identification and cluster analysis of Streptococcus pyogenes, however, has not been reported. The goal of our study was to evaluate this approach for the rapid identification and typing of S. pyogenes.

Methods

65 S. pyogenes isolates were obtained from the hospital. The samples were prepared and MALDI-TOF MS measurements were conducted as previously reported. Identification of unknown spectra was performed via a pattern recognition algorithm with a reference spectra and a dendrogram was constructed using the statistical toolbox in Matlab 7.1 integrated in the MALDI Biotyper 2.0 software.

Results

For identification, 61 of 65 S. pyogenes isolates could be identified correctly by MALDI-TOF MS with BioType 2.0 when compared to biochemical identification (API Strep), with an accuracy of 93.85%. In clustering analysis, 44 of 65 isolates were in accordance with those established by M typing, with a matching rate of 67.69%. When only the M type prevalence in China was considered, 41 of 45 isolates were in agreement with M typing, with a matching rate of 91.1%.

Conclusions

It was here shown that MALDI-TOF MS with Soft Biotype 2.0 and its database could facilitate rapid identification of S. pyogenes. It may present an attractive alternative to traditional biochemical methods of identification. However, for classification, more isolates and advances in the MALDI-TOF MS technology are needed to improve accuracy.

Molecular markers for the study of streptococcal epidemiology

Diseases caused by Streptococcus pyogenes (Group A streptococcus, GAS) range from superficial infections such as pharyngitis and impetigo to potentially fatal rheumatic heart disease and invasive disease. Studies spanning emm-typing surveillance to population genomics are providing new insights into the epidemiology, pathogenesis, and biology of this organism. Such studies have demonstrated the differences that exist in the epidemiology of streptococcal disease between developing and developed nations. In developing nations, where streptococcal disease is endemic, the diversity of GAS emm-types circulating is much greater than that found in developed nations. An association between emm-type and disease, as observed in developed countries is also lacking. Intriguingly, comparative genetic studies suggest that emm-type is not always a good predictor of the evolutionary relatedness of geographically distant isolates. A view of GAS as a highly dynamic organism, in possession of a core set of virulence genes that contribute to host niche specialization and common pathogenic processes, augmented by accessory genes that change the relative virulence of specific lineages is emerging. Our inability to definitively identify genetic factors that contribute to specific disease outcome underscores the complex nature of streptococcal diseases.

Whole-genome association study on tissue tropism phenotypes in group A Streptococcus

Group A Streptococcus (GAS) has a rich evolutionary history of horizontal transfer among its core genes. Yet, despite extensive genetic mixing, GAS strains have discrete ecological phenotypes. To further our understanding of the molecular basis for ecological phenotypes, comparative genomic hybridization of a set of 97 diverse strains to a GAS pangenome microarray was undertaken, and the association of accessory genes with emm genotypes that define tissue tropisms for infection was determined. Of the 22 nonprophage accessory gene regions (AGRs) identified, only 3 account for all statistically significant linkage disequilibrium among strains having the genotypic biomarkers for throat versus skin infection specialists. Networked evolution and population structure analyses of loci representing each of the AGRs reveal that most strains with the skin specialist and generalist biomarkers form discrete clusters, whereas strains with the throat specialist biomarker are highly diverse. To identify coinherited and coselected accessory genes, the strength of genetic associations was determined for all possible pairwise combinations of accessory genes among the 97 GAS strains. Accessory genes showing very strong associations provide the basis for an evolutionary model, which reveals that a major transition between many throat and skin specialist haplotypes correlates with the gain or loss of genes encoding fibronectin-binding proteins. This study employs a novel synthesis of tools to help delineate the major genetic changes associated with key adaptive shifts in an extensively recombined bacterial species.

Defense from the Group A Streptococcus by active and passive vaccination with the streptococcal hemoprotein receptor

BACKGROUND

The worldwide burden of the Group A Streptococcus (GAS) primary infection and sequelae is considerable, although immunization programs with broad coverage of the hyper variable GAS are still missing. We evaluate the streptococcal hemoprotein receptor (Shr), a conserved streptococcal protein, as a vaccine candidate against GAS infection.

METHODS

Mice were immunized intraperitoneally with purified Shr or intranasally with Shr-expressing Lactococcus lactis. The resulting humoral response in serum and secretions was determined. We evaluated protection from GAS infection in mice after active or passive vaccination with Shr, and Shr antiserum was tested for bactericidal activity.

RESULTS

A robust Shr-specific immunoglobulin (Ig) G response was observed in mouse serum after intraperitoneal vaccination with Shr. Intranasal immunization elicited both a strong IgG reaction in the serum and a specific IgA reaction in secretions. Shr immunization in both models allowed enhanced protection from systemic GAS challenge. Rabbit Shr antiserum was opsonizing, and mice that were administrated with Shr antiserum prior to the infection demonstrated a significantly higher survival rate than did mice treated with normal rabbit serum.

CONCLUSIONS

Shr is a promising vaccine candidate that is capable of eliciting bactericidal antibody response and conferring immunity against systemic GAS infection in both passive and active vaccination models.

emm gene diversity, superantigen gene profiles and presence of SlaA among clinical isolates of group A, C and G streptococci from western Norway

In order to investigate molecular characteristics of beta-hemolytic streptococcal isolates from western Norway, we analysed the entire emm gene sequences, obtained superantigen gene profiles and determined the prevalence of the gene encoding streptococcal phospholipase A2 (SlaA) of 165 non-invasive and 34 contemporary invasive group A, C and G streptococci (GAS, GCS and GGS). Among the 25 GAS and 26 GCS/GGS emm subtypes identified, only emm3.1 was significantly associated with invasive disease. M protein size variation within GAS and GCS/GGS emm types was frequently identified. Two non-invasive and one invasive GGS possessed emm genes that translated to truncated M proteins as a result of frameshift mutations. Results suggestive of recombinations between emm or emm-like gene segments were found in isolates of emm4 and stG485 types. One non-invasive GGS possessed speC, speG, speH, speI and smeZ, and another non-invasive GGS harboured SlaA. speA and SlaA were over-represented among invasive GAS, probably because they were associated with emm3. speG^dys was identified in 83% of invasive and 63% of non-invasive GCS/GGS and correlated with certain emm subtypes. Our results indicate the invasive potential of isolates belonging to emm3, and show substantial emm gene diversity and possible lateral gene transfers in our streptococcal population.

Progress in the development of effective vaccines to prevent selected gram-positive bacterial infections

Infections caused by virulent Gram-positive bacteria, such as Staphylococcus aureus, group B streptococci and group A streptococci, remain significant causes of morbidity and mortality despite progress in antimicrobial therapy. Despite significant advances in the understanding of the pathogenesis of infection caused by these organisms, there are only limited strategies to prevent infection. In this article, we review efforts to develop safe and effective vaccines that would prevent infections caused by these 3 pathogens.

Protective efficacy of group A streptococcal vaccines containing type-specific and conserved M protein epitopes

The amino terminal region of group A streptococcal M proteins evokes type-specific immunity while the conserved C-repeat epitopes evoke cross-protective immunity against multiple serotypes. The present studies were undertaken to compare the protective efficacy of vaccines containing either type-specific (hexavalent vaccine) or conserved C-repeat (J14 vaccine) M protein epitopes and to determine if combination vaccines resulted in enhanced levels of protection. Our results indicated that the protective efficacy of the type-specific vaccine was significantly greater than that of J14 and that the addition of J14 to vaccine formulations did not enhance the level of protection achieved with type-specific formulations.

Tissue tropisms in group A streptococcal infections

Group A Streptococcus (GAS) is a human-specific pathogen that is highly prevalent throughout the world. The vast majority of GAS infections lead to a mild disease involving the epithelial surfaces of either the throat or skin. The concept of distinct sets of 'throat' and 'skin' strains of GAS has long been conceived. From an ecological standpoint, the epithelium of the throat and skin are important because it is where the organism is most successful in reproducing and transmitting to new hosts. This article examines key features of the epidemiology, population biology and molecular pathogenesis that underlie the tissue site preferences for infection exhibited by GAS, with an emphasis on work from our laboratory on skin tropisms. Recombinational replacement with orthologous gene forms, following interspecies transfer, appears to be an important genetic step leading up to the exploitation of new niches by GAS.

Differences among group A streptococcus epidemiological landscapes: consequences for M protein-based vaccines?

Group A streptococcus (GAS) is a bacterial pathogen responsible for a wide array of disease pathologies in humans. GAS surface M protein plays multiple key roles in pathogenesis, and serves as a target for typing and vaccine development. In this review, we have compiled GAS epidemiological studies from several countries around the world to highlight the consequences on the theoretical efficacy of two different M protein-based vaccine strategies.

Group A streptococcal vaccines: facts versus fantasy

PURPOSE OF REVIEW

This review provides an overview of progress of the development of group A streptococcal (GAS) vaccines with a focus on recent advances.

RECENT FINDINGS

Historically, GAS vaccine development has focused on the N-terminus of the M protein, which ultimately led to successful phase I/II clinical trials of a 26-valent recombinant M protein vaccine in 2004-2005. More recently, interest in antigens conserved among most, if not all, group A streptococci has increased. However, no vaccines containing these antigens have reached clinical trials. Three strategies have been used to develop conserved antigen vaccine candidates: use of the conserved region of the M protein; use of well described virulence factors as antigens, including streptococcal C5a peptidase, streptococcal carbohydrate, fibronectin-binding proteins, cysteine protease and streptococcal pili; and use of reverse vaccinology to identify novel antigens.

SUMMARY

Several vaccine candidates against GAS infection are in varying stages of preclinical and clinical development. Although there is great hope that one of these vaccine candidates will reach licensure in the next decade, only one, the multivalent N-terminal vaccine, has entered clinical trials in the last 30 years. Although strong advocacy for GAS vaccine development is important, there remains an urgent need to institute available public health control measures against GAS diseases globally, particularly in developing countries.

Acute rheumatic fever and rheumatic heart disease in indigenous populations

Acute rheumatic fever and rheumatic heart disease are diseases of socioeconomic disadvantage. These diseases are common in developing countries and in Indigenous populations in industrialized countries. Clinicians who work with Indigenous populations need to maintain a high index of suspicion for the potential diagnosis of acute rheumatic fever, particularly in patients presenting with joint pain. Inexpensive medicines, such as aspirin, are the mainstay of symptomatic treatment of rheumatic fever; however, antiinflammatory treatment has no effect on the long-term rate of progression or severity of chronic valvular disease. The current focus of global efforts at prevention of rheumatic heart disease is on secondary prevention (regular administration of penicillin to prevent recurrent rheumatic fever), although primary prevention (timely treatment of streptococcal pharyngitis to prevent rheumatic fever) is also important in populations in which it is feasible.