Interplay between group A Streptococcus and host innate immune responses

SUMMARYGroup A Streptococcus (GAS), also known as Streptococcus pyogenes, is a clinically well-adapted human pathogen that harbors rich virulence determinants contributing to a broad spectrum of diseases. GAS is capable of invading epithelial, endothelial, and professional phagocytic cells while evading host innate immune responses, including phagocytosis, selective autophagy, light chain 3-associated phagocytosis, and inflammation. However, without a more complete understanding of the different ways invasive GAS infections develop, it is difficult to appreciate how GAS survives and multiplies in host cells that have interactive immune networks. This review article attempts to provide an overview of the behaviors and mechanisms that allow pathogenic GAS to invade cells, along with the strategies that host cells practice to constrain GAS infection. We highlight the counteractions taken by GAS to apply virulence factors such as streptolysin O, nicotinamide-adenine dinucleotidase, and streptococcal pyrogenic exotoxin B as a hindrance to host innate immune responses.

Group A streptococcal collagen-like protein 1 restricts tumor growth in murine pancreatic adenocarcinoma and inhibits cancer-promoting neutrophil extracellular traps

Introduction

Pancreatic ductal adenocarcinoma (PDAC) is a lethal cancer associated with an immunosuppressive environment. Neutrophil extracellular traps (NETs) were initially described in the context of infection but have more recently been implicated in contributing to the tolerogenic immune response in PDAC. Thus, NETs are an attractive target for new therapeutic strategies. Group A Streptococcus (GAS) has developed defensive strategies to inhibit NETs.

Methods

In the present work, we propose utilizing intra-tumoral GAS injection to stimulate anti-tumor activity by inhibiting cancer-promoting NETs. Mice harboring Panc02 or KPC subcutaneous tumors injected with three different M-type GAS strains. Tumors and spleens were harvested at the endpoint of the experiments to assess bacterial colonization and systemic spread, while sera were analyzed for humoral responses toward the streptococcal antigens, especially the M1 and Scl1 proteins. Role of the streptococcal collagen-like protein 1 (Scl1) in anti-PDAC activity was assessed in vivo after intratumoral injection with M1 GAS wild-type, an isogenic mutant strain devoid of Scl1, or a complemented mutant strain with restored scl1 expression. In addition, recombinant Scl1 proteins were tested for NET inhibition using in vitro and ex vivo assays assessing NET production and myeloperoxidase activity.

Results

Injection of three different M-type GAS strains reduced subcutaneous pancreatic tumor volume compared to control in two different murine PDAC models. Limitation of tumor growth was dependent on Scl1, as isogenic mutant strain devoid of Scl1 did not reduce tumor size. We further show that Scl1 plays a role in localizing GAS to the tumor site, thereby limiting the systemic spread of bacteria and off-target effects. While mice did elicit a humoral immune response to GAS antigens, tested sera were weakly immunogenic toward Scl1 antigen following intra-tumoral treatment with Scl1-expressing GAS. M1 GAS inhibited NET formation when co-cultured with neutrophils while Scl1-devoid mutant strain did not. Recombinant Scl1 protein inhibited NETs ex vivo in a dose-dependent manner by suppressing myeloperoxidase activity.

Discussion

Altogether, we demonstrate that intra-tumoral GAS injections reduce PDAC growth, which is facilitated by Scl1, in part through inhibition of cancer promoting NETs. This work offers a novel strategy by which NETs can be targeted through Scl1 protein and potentiates its use as a cancer therapeutic.

Use of saliva-based qPCR diagnostics for the accurate, rapid, and inexpensive detection of strep throat

OBJECTIVES

Outpatient health care facilities are essential for quickly diagnosing common infectious diseases such as bacterial and viral pharyngitis. The only form of pharyngitis requiring antibiotics is strep throat (ST); however, antibiotic prescription rates are much higher than ST prevalence, suggesting antibiotics are being inappropriately prescribed. Current rapid ST diagnostics may be contributing to this problem due to the low sensitivity and variable specificity of these tests. It is best practice to verify a negative ST diagnosis with a group A Streptococcus (GAS) culture, but many clinics do not perform this test due to the additional cost and 24-72 h required to obtain results. This indicates there is great need for more accurate rapid diagnostic tools in outpatient facilities. We hypothesized that next generation qPCR technology could be adapted to detect GAS DNA from saliva samples (instead of the traditional throat swab) by creating a simple, fast, and inexpensive protocol.

METHODS

Saliva specimens collected from patients at James Madison University Health Center were used to test the effectiveness of our Chelex 100-based rapid DNA extraction method, followed by a fast protocol developed for the Open qPCR machine to accurately detect ST.

RESULTS

Our final saliva processing and qPCR protocol required no specialized training to perform and was able to detect ST with 100 % sensitivity and 100 % specificity (n=102) in 22-26 min, costing only $1.12 per sample.

CONCLUSIONS

Saliva can be rapidly analyzed via qPCR for the accurate and inexpensive detection of ST.

The Group A Streptococcal Vaccine Candidate VAX-A1 Protects against Group B Streptococcus Infection via Cross-Reactive IgG Targeting Virulence Factor C5a Peptidase

Group B Streptococcus (Streptococcus agalactiae or GBS) is the leading infectious cause of neonatal mortality, causing roughly 150,000 infant deaths and stillbirths annually across the globe. Approximately 20% of pregnant women are asymptomatically colonized by GBS, which is a major risk factor for severe fetal and neonatal infections as well as preterm birth, low birth weight, and neurodevelopmental abnormalities. Current clinical interventions for GBS infection are limited to antibiotics, and no vaccine is available. We previously described VAX-A1 as a highly effective conjugate vaccine against group A Streptococcus that is formulated with three antigens, SpyAD, streptolysin O, and C5a peptidase (ScpA). ScpA is a surface-expressed, well-characterized GAS virulence factor that shares nearly identical sequences with the lesser studied GBS homolog ScpB. Here, we show that GBS C5a peptidase ScpB cleaves human complement factor C5a and contributes to disease severity in the murine models of pneumonia and sepsis. Furthermore, antibodies elicited by GAS C5a peptidase bind to GBS in an ScpB-dependent manner, and VAX-A1 immunization protects mice against lethal GBS heterologous challenge. These findings support the contribution of ScpB to GBS virulence and underscore the importance of choosing vaccine antigens; a universal GAS vaccine such as VAX-A1 whose formulation includes GAS C5a peptidase may have additional benefits through some measure of cross-protection against GBS infections.

Estimating predictors of severity of group A Streptococcus infection in pregnancy

OBJECTIVE

To identify the clinical characteristics of pregnancy associated group A streptococcus (GAS) infection and predictors for intensive care unit (ICU) admission.

METHODS

A retrospective cohort study of culture-proven pregnancy-related GAS infections in tertiary hospital Electronic medical records were reviewed, for cases of cultures positive GAS that were identified between January 2008 and July 2021. A GAS infection was defined by the isolation of the pathogen from a sterile liquid or tissue site. Blood and urine cultures were obtained from all patients with peripartum hyperpyrexia (fever >38 °C). Medical Personnel screening included cultures of the throat, rectum, and skin lesions (if present). In cases of hemodynamic instability patients were transferred ad hoc to ICU, according to the obstetrician and intensivist judgment.

RESULTS

Of the 143,750 who delivered during the study period, 66 (0.04%) were diagnosed as having a pregnancy associated GAS infection. Of these, 57 patients presented postpartum, and represented the study cohort. The most common presenting signs and symptoms among puerperal GAS, were postpartum pyrexia (72%), abdominal pain (33%), and tachycardia (>100 bpm, 22%). 12 women (21.0%) developed streptococcal toxic shock syndrome (STSS. Predictors for STSS and ICU admission were: antibiotic administration >24 h from presentation postpartum, tachycardia, and a C-reactive protein level >200 mg/L. Women that received antibiotic prophylaxis during labor had a significantly lower rate of STSS (0 vs 10, 22.7%; p = .04).

CONCLUSION

Deferral of medical intervention >24 h from the first registered abnormal sign had the most important impact on deterioration of women with invasive puerperal GAS. Antibiotic prophylaxis during labor in women with GAS may reduce associated complications.

Comparison of Adjuvant Clindamycin vs Linezolid for Severe Invasive Group A Streptococcus Skin and Soft Tissue Infections

Background

Linezolid may be an option for severe group A Streptococcus (GAS) infections based on its potent in vitro activity and antitoxin effects, but clinical data supporting its use over clindamycin are limited. This study evaluated treatment outcomes in patients with severe GAS skin and soft tissue infections who received either linezolid or clindamycin.

Methods

This retrospective single-center cohort study examined patients with GAS isolated from blood and/or tissue cultures with invasive soft tissue infection or necrotizing fasciitis who underwent surgical debridement and received linezolid or clindamycin for at least 48 hours. The primary outcome was percentage change in Sequential Organ Failure Assessment (SOFA) score from baseline through 72 hours of hospitalization.

Results

After adjustment for time to first surgical intervention among patients with a baseline SOFA score >0 (n = 23 per group), there was no difference in reduction of SOFA score over the first 72 hours in patients receiving clindamycin vs linezolid. In the entire cohort (n = 26, clindamycin; n = 29, linezolid), there was no difference in inpatient mortality (2% vs 1%) or any secondary outcomes, including duration of vasopressor therapy, intensive care unit length of stay, and antibiotic-associated adverse drug events.

Conclusions

There was no difference in reduction of critical illness as measured by SOFA score between baseline and 72 hours among patients treated with clindamycin vs linezolid. Given its more favorable side effect profile, linezolid may be a viable option for the treatment of serious GAS infections and should be further studied.

A core-genome multilocus sequence typing scheme for the detection of genetically related Streptococcus pyogenes clusters

The recently observed increase in invasive Streptococcus pyogenes infections causes concern in Europe. However, conventional molecular typing methods lack discriminatory power to aid investigations of outbreaks caused by S. pyogenes. Therefore, there is an urgent need for high-resolution molecular typing methods to assess genetic relatedness between S. pyogenes isolates. In the current study, we aimed to develop a novel high-resolution core-genome multilocus sequence typing (cgMLST) scheme for S. pyogenes and compared its discriminatory power to conventional molecular typing methods. The cgMLST scheme was designed with the commercial Ridom SeqSphere+ software package. To define a cluster threshold, the scheme was evaluated using publicly available data from nine defined S. pyogenes outbreaks in the United Kingdom. The cgMLST scheme was then applied to 23 isolates from a suspected S. pyogenes outbreak and 117 S. pyogenes surveillance isolates both from the Netherlands. MLST and emm-typing results were used for comparison to cgMLST results. The allelic differences between isolates from defined outbreaks ranged between 6 and 31 for isolates with the same emm-type, resulting in a proposed cluster threshold of <5 allelic differences out of 1,095 target loci. Seven out of twenty-three (30%) isolates from the suspected outbreak had an allelic difference of <2, thereby identifying a potential cluster that could not be linked to other isolates. The proposed cgMLST scheme shows a higher discriminatory ability when compared to conventional typing methods. The rapid and simple analysis workflow allows for extended detection of clusters of potential outbreak isolates and surveillance and may facilitate the sharing of sequencing results between (inter)national laboratories.

Mucosal Immunization Has Benefits over Traditional Subcutaneous Immunization with Group A Streptococcus Antigens in a Pilot Study in a Mouse Model

Group A Streptococcus (GAS) is a major human pathogen for which there is no licensed vaccine. To protect against infection, a strong systemic and mucosal immune response is likely to be necessary to prevent initial colonization and any events that might lead to invasive disease. A broad immune response will be necessary to target the varied GAS serotypes and disease presentations. To this end, we designed a representative panel of recombinant proteins to cover the stages of GAS infection and investigated whether mucosal and systemic immunity could be stimulated by these protein antigens. We immunized mice sublingually, intranasally and subcutaneously, then measured IgG and IgA antibody levels and functional activity through in vitro assays. Our results show that both sublingual and intranasal immunization in the presence of adjuvant induced both systemic IgG and mucosal IgA. Meanwhile, subcutaneous immunization generated only a serum IgG response. The antibodies mediated binding and killing of GAS cells and blocked binding of GAS to HaCaT cells, particularly following intranasal and subcutaneous immunizations. Further, antigen-specific assays revealed that immune sera inhibited cleavage of IL-8 by SpyCEP and IgG by Mac/IdeS. These results demonstrate that mucosal immunization can induce effective systemic and mucosal antibody responses. This finding warrants further investigation and optimization of humoral and cellular responses as a viable alternative to subcutaneous immunization for urgently needed GAS vaccines.

Detoxification of reactive oxygen species by the hyaluronic acid capsule of group A Streptococcus

The pro-inflammatory cytokine IL-6 regulates antimicrobial responses that are broadly crucial in the defense against infection. Our prior work shows that IL-6 promotes the killing of the M4 serotype group A Streptococcus (GAS) but does not impact the globally disseminated M1T1 serotype associated with invasive infections. Using in vitro and in vivo infection models, we show that IL-6 induces phagocyte reactive oxygen species (ROS) that are responsible for the differential susceptibility of M4 and M1T1 GAS to IL-6-mediated defenses. Clinical isolates naturally deficient in capsule, or M1T1 strains deficient in capsule production, are sensitive to this ROS killing. The GAS capsule is made of hyaluronic acid, an antioxidant that detoxifies ROS and can protect acapsular M4 GAS when added exogenously. During in vitro interactions with macrophages and neutrophils, acapsular GAS can also be rescued with the antioxidant N-acetylcysteine, suggesting this is a major virulence contribution of the capsule. In an intradermal infection model with gp91phox -/- (chronic granulomatous disease [CGD]) mice, phagocyte ROS production had a modest effect on bacterial proliferation and the cytokine response but significantly limited the size of the bacterial lesion in the skin. These data suggest that the capsule broadly provides enhanced resistance to phagocyte ROS but is not essential for invasive infection. Since capsule-deficient strains are observed across several GAS serotypes and are competent for transmission and both mild and invasive infections, additional host or microbe factors may contribute to ROS detoxification during GAS infections.

Changes in Group A Streptococcus emm Types Associated with Invasive Infections in Adults, Spain, 2023

An increase in invasive group A Streptococcus infection was detected in the northeast of Spain in November 2022. A postpandemic decline in the diversity of circulating emm types involved in invasive group A Streptococcus was observed, along with the emergence of emm49 in this geographic area.

Group A Streptococcus Primary Peritonitis in Children, New Zealand

Group A Streptococcus (GAS) primary peritonitis is a rare cause of pediatric acute abdomen (sudden onset of severe abdominal pain); only 26 pediatric cases have been reported in the English language literature since 1980. We discuss 20 additional cases of pediatric primary peritonitis caused by GAS among patients at Starship Children's Hospital, Auckland, New Zealand, during 2010-2022. We compare identified cases of GAS primary peritonitis to cases described in the existing pediatric literature. As rates of rates of invasive GAS increase globally, clinicians should be aware of this cause of unexplained pediatric acute abdomen.

Naturally acquired functional antibody responses to group A Streptococcus differ between major strain types

Group A Streptococcus (GAS) is a leading human pathogen for which there is no licensed vaccine. Infections are most common in young children and the elderly suggesting immunity accumulates with exposure until immune senescence in older age. Though protection has been postulated to be strain type specific, based on the M-protein (emm-type), the antigenic basis of population-level immunity remains poorly understood. Naturally acquired GAS antibody responses were investigated using intravenous immunoglobulin (IVIG), which contains pooled immunoglobulins from thousands of healthy human donors, as a surrogate for population immunity. Functional opsonophagocytic killing assays were conducted with GAS strains (n = 6) representing the three major emm-pattern types (emm12, A-C pattern; emm53, D-pattern; and emm75, E-pattern). While IVIG induced opsonophagocytic killing of all GAS strains tested, specificity assays showed the profile of protective antibodies differed considerably between emm-types. Antibodies targeting the M-protein were a major component of the functional IVIG antibody response for emm12 and emm53 strains but not for emm75 strains. The striking differences in the contribution of M-protein specific antibodies to killing suggest naturally acquired immunity differs between strains from the major emm-patterns. This challenges the dogma that M-protein is the primary protective antigen across all GAS straintypes. IMPORTANCE Group A Streptococcus (GAS) is a globally important pathogen. With the surge of invasive GAS infections that have occurred in multiple countries, contemporaneous with the relaxation of COVID-19 pandemic restrictions, there is increased interest in the mechanisms underpinning GAS immunity. We utilized intravenous immunoglobulin (IVIG), pooled immunoglobulins from thousands of healthy donors, as a surrogate for population-level immunity to GAS, and explored the contribution of strain-specific (M-type specific) antibodies to GAS immunity using functional killing assays. This revealed striking differences between major strain types as to the contribution of strain specific antibodies to killing. For GAS strains belonging to the E pattern group, M-type specific antibodies do not mediate killing and immunity, which contrasts with strains belonging to pattern A-C and D groups. This challenges the historical dogma, originally proposed by Rebecca Lancefield in the 1950-1960s, that the M-protein is the major protective antigen across all GAS strain types.

An outbreak of acute rheumatic fever in a remote Aboriginal community

OBJECTIVES

We describe the public health response to an outbreak of acute rheumatic fever (ARF) in a remote Aboriginal community.

METHODS

In August 2021, the Northern Territory Rheumatic Heart Disease Control Program identified an outbreak of acute rheumatic fever in a remote Aboriginal community. A public health response was developed using a modified acute poststreptococcal glomerulonephritis protocol and the National Acute Rheumatic Fever Guideline for Public Health Units.

RESULTS

12 cases were diagnosed during the outbreak; six-times the average number of cases in the same period in the five years prior (n=1.8). Half (n=6) of the outbreak cases were classified as recurrent episodes with overdue secondary prophylaxis. Contact tracing and screening of 11 households identified 86 close contacts.

CONCLUSIONS

This outbreak represented an increase in both first episodes and recurrences of acute rheumatic fever and highlights the critical need for strengthened delivery of acute rheumatic fever secondary prophylaxis, and for improvements to the social determinants of health in the region.

IMPLICATIONS FOR PUBLIC HEALTH

Outbreaks of acute rheumatic fever are rare despite continuing high rates of acute rheumatic fever experienced by remote Aboriginal communities. Nevertheless, there can be improvements in the current national public health guidance relating to acute rheumatic fever cluster and outbreak management.

Primary Peritonitis due to Group A Streptococcus Successfully Treated with Intraperitoneal Drainage

A 42-year-old woman was admitted to our hospital because of lower abdominal pain and diarrhea. Although the initial symptoms and imaging findings were similar to those of acute enteritis, blood and ascites cultures led to the diagnosis of primary peritonitis caused by group A Streptococcus. In many cases, the disease rapidly deteriorates, and laparotomy is performed for the early diagnosis and to reduce the number of bacteria in the abdominal cavity. In the present case, intraperitoneal drainage was effective for avoiding surgery. We suggest that intraperitoneal drainage is effective for the treatment of this disease.

Intravenous versus Partial Oral Antibiotic Therapy in the Treatment of Uncomplicated Bloodstream Infection Due to Streptococcus Species

This retrospective cohort study examines effectiveness of partial oral antibiotic regimens in uncomplicated bloodstream infections (BSIs) due to Streptococcus species compared to standard intravenous therapy. Adult patients with uncomplicated streptococcal BSIs from April 2016 to June 2020 in seven hospitals in South Carolina, USA, were evaluated. Multivariate Cox proportional hazards regression was used to examine the time to treatment failure within 90 days of a BSI after adjustment for the propensity to receive partial oral therapy. Multivariate linear regression was used to examine the hospital length of stay (HLOS). Among the 222 patients included, 99 received standard intravenous antibiotics and 123 received partial oral therapy. Of the standard intravenous therapy group, 46/99 (46.5%) required outpatient parenteral antibiotic therapy (OPAT). There was no difference in the risk of treatment failure between partial oral and standard intravenous therapy (hazards ratio 0.53, 95% CI 0.18, 1.60; p = 0.25). Partial oral therapy was independently associated with a shorter HLOS after adjustments for the propensity to receive partial oral therapy and other potential confounders (-2.23 days, 95% CI -3.53, -0.94; p < 0.001). Transitioning patients to oral antibiotics may be a reasonable strategy in the management of uncomplicated streptococcal BSIs. Partial oral therapy does not seem to have a higher risk of treatment failure and may spare patients from prolonged hospitalizations and OPAT complications.

Group A Streptococcus Meningitis in Adults, Denmark

We report a 21-fold increase in group A Streptococcus meningitis in adults in Denmark during October 13, 2022-April 12, 2023, concurrent with an outbreak of invasive streptococcal disease. We describe clinical characteristics of the outbreak cases and prognosis for patients in comparison to those for previous sporadic cases.

Methylome-dependent transformation of emm1 group A streptococci

Genetic intractability presents a fundamental barrier to the manipulation of bacteria, hindering advancements in microbiological research. Group A Streptococcus (GAS), a lethal human pathogen currently associated with an unprecedented surge of infections worldwide, exhibits poor genetic tractability attributed to the activity of a conserved type 1 restriction modification system (RMS). RMS detect and cleave specific target sequences in foreign DNA that are protected in host DNA by sequence-specific methylation. Overcoming this "restriction barrier" thus presents a major technical challenge. Here, we demonstrate for the first time that different RMS variants expressed by GAS give rise to genotype-specific and methylome-dependent variation in transformation efficiency. Furthermore, we show that the magnitude of impact of methylation on transformation efficiency elicited by RMS variant TRDAG, encoded by all sequenced strains of the dominant and upsurge-associated emm1 genotype, is 100-fold greater than for all other TRD tested and is responsible for the poor transformation efficiency associated with this lineage. In dissecting the underlying mechanism, we developed an improved GAS transformation protocol, whereby the restriction barrier is overcome by the addition of the phage anti-restriction protein Ocr. This protocol is highly effective for TRDAG strains including clinical isolates representing all emm1 lineages and will expedite critical research interrogating the genetics of emm1 GAS, negating the need to work in an RMS-negative background. These findings provide a striking example of the impact of RMS target sequence variation on bacterial transformation and the importance of defining lineage-specific mechanisms of genetic recalcitrance. IMPORTANCE Understanding the mechanisms by which bacterial pathogens are able to cause disease is essential to enable the targeted development of novel therapeutics. A key experimental approach to facilitate this research is the generation of bacterial mutants, through either specific gene deletions or sequence manipulation. This process relies on the ability to transform bacteria with exogenous DNA designed to generate the desired sequence changes. Bacteria have naturally developed protective mechanisms to detect and destroy invading DNA, and these systems severely impede the genetic manipulation of many important pathogens, including the lethal human pathogen group A Streptococcus (GAS). Many GAS lineages exist, of which emm1 is dominant among clinical isolates. Based on new experimental evidence, we identify the mechanism by which transformation is impaired in the emm1 lineage and establish an improved and highly efficient transformation protocol to expedite the generation of mutants.

State of the Art of Invasive Group A Streptococcus Infection in Children: A Scoping Review of the Literature with a Focus on Predictors of Invasive Infection

Currently, it remains unclear why some children develop invasive group A Streptococcus (iGAS) and how to manage this condition. Therefore, to explore available works in the literature, we performed a scoping review aiming to analyze the current literature on clinical presentation of different illnesses outcomes of iGAS, with a specific focus on predictors of invasive infection, including an assessment of the prodromal stages of the disease and the possible presence of previous non-invasive GAS infections in children that later developed iGAS.

METHODS

We conducted a systematic search on PubMed and SCOPUS of all pediatric studies reporting iGAS cases, following the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) checklist. For those studies in which multivariable analysis investigating iGAS risk factors was performed, a second review was performed and reported in detail.

RESULTS

A total of 209 studies were included. Five studies investigated risk factors for iGAS, the most relevant being varicella infection, chronic underlying illness, presence of the speC gene in GAS strains, acetaminophen and ibuprofen use, children nonwhite, living in low-income households, exposure to varicella at home, persistent high fever, having more than one other child in the home, and new use of NSAIDs. Although we observed a progressive increase in the number of papers published on this topic, no trials investigating the benefits of clindamycin or intravenous immunoglobulins were found and low-to-middle-income countries were found to be poorly represented in the current literature.

CONCLUSIONS

Our scoping review highlights important gaps regarding several aspects of iGAS in children, including prodromic presentation and optimal treatment strategies. There is also little representation of low-middle-income countries. The current literature does not allow the performance of systematic reviews or meta-analyses, but this work should inform healthcare professionals, policy makers, and funding agencies on which studies to prioritize on this topic.

Epidemiology of Group A Streptococcal bacteraemia in Hunter New England Local Health District, 2008 to 2019

Invasive Group A Streptococcal infection (iGAS) is an uncommon but serious infection with Streptococcus pyogenes in a normally sterile body site. Manifestations include bacteraemia, necrotising fasciitis and toxic shock syndrome with attendant serious morbidity and mortality. An increasing incidence of iGAS has been observed in some regions of Australia. iGAS became a nationally notifiable condition from 1 July 2021. To determine if regional incidence has increased, and to identify priority populations, we undertook a retrospective data analysis of Group A Streptococcal (GAS) bacteraemia cases in Hunter New England Local Health District (HNELHD), New South Wales, Australia, from 1 January 2008 to 31 December 2019, as identified by NSW Health Pathology, John Hunter Hospital. A total of 486 cases were identified (age-standardised rate: 4.05 cases per 100,000 population per year). Incidence in HNELHD gradually increased over the study period (adjusted incidence rate ratio: 1.04; 95% confidence interval: 1.01-1.07) and was significantly higher in children under 5 years of age; in adults over 70 years of age; in males; and in First Nations peoples. A significant peak occurred in 2017 (9.00 cases per 100,000 population), the cause of which remains unclear. GAS bacteraemia is uncommon but severe, and incidence in HNELHD has slowly increased. Public health and clinical guidelines must address the needs of priority populations, which include young children, older adults and First Nations peoples. Routine surveillance and genomic analysis will help improve our understanding of iGAS and inform best public health management.

Insertion of an immunodominant T helper cell epitope within the Group A Streptococcus M protein promotes an IFN-γ-dependent shift from a non-protective to a protective immune response

The common pathogen Group A Streptococcus (GAS, Streptococcus pyogenes) is an extracellular bacterium that is associated with a multitude of infectious syndromes spanning a wide range of severity. The surface-exposed M protein is a major GAS virulence factor that is also target for protective antibody responses. In this study, we use a murine immunization model to investigate aspects of the cellular and molecular foundation for protective adaptive immune responses generated against GAS. We show that a wild type M1 GAS strain induces a non-protective antibody response, while an isogenic strain carrying the immunodominant 2W T helper cell epitope within the M protein elicits an immune response that is protective against the parental non-recombinant M1 GAS strain. Although the two strains induce total anti-GAS IgG levels of similar magnitude, only the 2W-carrying strain promotes elevated titers of the complement-fixing IgG2c subclass. Protection is dependent on IFN-γ, and IFN-γ-deficient mice show a specific reduction in IgG2c levels. Our findings suggest that inclusion of the 2W T cell epitope in the M protein confers essential qualitative alterations in the adaptive immune response against GAS, and that sparsity in IFN-γ-promoting Th cell epitopes in the M protein may constitute an immune evasion mechanism, evolved to allow the pathogen to avoid attack by complement-fixing antibodies.

Activity Relationship of Poly(ethylenimine)-Based Liposomes as Group A Streptococcus Vaccine Delivery Systems

Untreated group A Streptococcus (GAS) can lead to a range of life-threatening diseases, including rheumatic heart disease. To date, no therapeutic or prophylactic vaccines are commercially available to treat or prevent GAS infection. Development of a peptide-based subunit vaccine offers a promising solution, negating the safety issues of live-attenuated or inactive vaccines. Subunit vaccines administer small peptide fragments (antigens), which are typically poorly immunogenic. Therefore, these peptide antigens require formulation with an immune stimulant and/or vaccine delivery platform to improve their immunogenicity. We investigated polyelectrolyte complexes (PECs) and polymer-coated liposomes as self-adjuvanting delivery vehicles for a GAS B cell peptide epitope conjugated to a universal T-helper epitope and a synthetic toll-like receptor 2-targeting moiety lipid core peptide-1 (LCP-1). A structure-activity relationship of cationic PEC vaccines containing different external PEI-coatings (poly(ethylenimine); 10 kDa PEI, 25 kDa PEI, and a synthetic mannose-functionalized 25 kDa PEI) formed vaccines PEC-1, PEC-2, and PEC-3, respectively. All three PEC vaccines induced J8-specific systemic immunoglobulin G (IgG) antibodies when administered intranasally to female BALB/c mice without the use of additional adjuvants. Interestingly, PEC-3 induced the highest antibody titers among all tested vaccines, with the ability to effectively opsonize two clinically isolated GAS strains. A comparative study of PEC-2 and PEC-3 with liposome-based delivery systems was performed subcutaneously. LCP-1 was incorporated into a liposome formulation (DPPC, DPPG and cholesterol), and the liposomes were externally coated with PEI (25 kDa; Lip-2) or mannosylated PEI (25 kDa; Lip-3). All liposome vaccines induced stronger humoral immune responses compared to their PEC counterparts. Notably, sera of mice immunized with Lip-2 and Lip-3 produced significantly higher opsonic activity against clinically isolated GAS strains compared to the positive control, P25-J8 emulsified with the commercial adjuvant, complete Freund's adjuvant (CFA). This study highlights the capability of a PEI-liposome system to act as a self-adjuvanting vehicle for the delivery of GAS peptide antigens and protection against GAS infection.

Successfully drug treatment for necrotizing fasciitis caused by Streptococcus pyogenes in 88-year-old patient

Necrotizing fasciitis (NF) is a rare soft-tissue infection generally treated by emergency surgical intervention. We report a case of successfully drug treatment for NF in older patient with comorbidities thus avoiding surgical intervention.

Increase of Severe Pulmonary Infections in Adults Caused by M1UK Streptococcus pyogenes, Central Scotland, UK

We characterized the epidemiology, host-pathogen characteristics, and outcomes of severe adult pulmonary Streptococcus pyogenes infections that coincided with a high community caseload in central Scotland, UK. The pulmonary infections had high illness and death rates and were associated with socioeconomic deprivation, influenza A co-infection, and the M1_UK lineage of S. pyogenes.

Increase in invasive group A streptococcal infections and emergence of novel, rapidly expanding sub-lineage of the virulent Streptococcus pyogenes M1 clone, Denmark, 2023

A highly virulent sub-lineage of the Streptococcus pyogenes M1 clone has been rapidly expanding throughout Denmark since late 2022 and now accounts for 30% of the new invasive group A streptococcal infections. We aimed to investigate whether a shift in variant composition can account for the high incidence rates observed over winter 2022/23, or if these are better explained by the impact of COVID-19-related restrictions on population immunity and carriage of group A Streptococcus.

Generation and characterization of a plasminogen-binding group A streptococcal M-protein/streptokinase-sensitive mouse line

BACKGROUND

Streptococcus pyogenes (GAS) is a human bacterial pathogen that generates various mild to severe diseases. Worldwide, there are approximately 700 million cases of GAS infections per year. In some strains of GAS, the surface-resident M-protein, plasminogen-binding group A streptococcal M-protein (PAM), binds directly to human host plasminogen (hPg), where it is activated to plasmin through a mechanism involving a Pg/bacterial streptokinase (SK) complex as well as endogenous activators. Binding to Pg and its activation are dictated by selected sequences within the human host Pg protein, making it difficult to generate animal models to study this pathogen.

OBJECTIVES

To develop a murine model for studying GAS infection by minimally modifying mouse Pg to enhance the affinity to bacterial PAM and sensitivity to GAS-derived SK.

METHODS

We used a targeting vector that contained a mouse albumin-promoter and mouse/human hybrid plasminogen cDNA targeted to the Rosa26 locus. Characterization of the mouse strain consisted of both gross and histological techniques and determination of the effects of the modified Pg protein through surface plasmon resonance measurements, Pg activation analyses, and mouse survival post-GAS infection.

RESULTS

We generated a mouse line expressing a chimeric Pg protein consisting of 2 amino acid substitutions in the heavy chain of Pg and a complete replacement of the mouse Pg light chain with the human Pg light chain.

CONCLUSION

This protein demonstrated an enhanced affinity for bacterial PAM and sensitivity to activation by the Pg-SK complex, making the murine host susceptible to the pathogenic effects of GAS.

Epidemiological Impact of the Pediatric Live Attenuated Influenza Vaccine (LAIV) Program on Group A Streptococcus (GAS) Infection in England

Background

Influenza is known to predispose to secondary bacterial infections including invasive group A streptococcal (iGAS) disease. The universal pediatric live attenuated influenza vaccine (LAIV) program introduced in England from the 2013/2014 influenza season was implemented incrementally, introducing cohorts of children annually to 2-16 years of coverage. Additionally, from the beginning of the program, discrete pilot areas offered LAIV vaccination to all primary school-age children, allowing for a unique comparison of infection rates between pilot and nonpilot areas during the program rollout.

Methods

Cumulative incidence rate ratios (IRRs) of GAS infections (all), scarlet fever (SF), and iGAS infection within each season by age group were compared for pilot and nonpilot areas using Poisson regression. The overall effect of the pilot program in the pre- (2010/2011-2012/2013 seasons) and postintroduction (2013/2014-2016/2017 seasons) periods was assessed using negative binomial regression by comparing changes in incidence between pilot/nonpilot areas (ratio of IRR [rIRR]).

Results

Reductions in IRRs of GAS and SF were observed within most post-LAIV program seasons, among the age groups 2-4 and 5-10 years. Significant reductions were seen among 5-10 years (rIRR, 0.57; 95% CI, 0.45-0.71; P < .001), 2-4 years (rIRR, 0.62; 95% CI, 0.43-0.90; P = .011), and 11-16 years (rIRR, 0.63; 95% CI, 0.43-0.90; P = .018) for GAS infections when assessing the overall effect of the program.

Conclusions

Our findings suggest that vaccination with LAIV may be associated with a reduced risk of GAS infection and support attaining high uptake of childhood influenza vaccination.

Emm type distribution of group A Streptococcus in China during 1990 and 2020: a systematic review and implications for vaccine coverage

Background

The recent increase of group A Streptococcus (GAS) infections in Europe has aroused global concern. We aim to provide molecular biological data for GAS prevention and control in China by analyzing the temporal shift of emm type.

Methods

We collected studies reporting GAS emm types in China from 1990 to 2020 by PRISMA statement and established a summary database including emm types and literature quality assessment. Based on the database we analyzed the geographic distribution of emm types from 1990 to 2020 and assessed the coverage of the known GAS 30-valent vaccine. Outbreak-associated emm types that had been reported over the past 30 years were also included.

Results

47 high quality studies were included for a systematic analysis of emm type distribution. This generated a database including totally 12,347 GAS isolates and 85 emm types. Shift of dominant emm type was witnessed during the past 30 years in China. In mainland China, dominant types changed from emm3, emm1, emm4, emm12 in 1990s to emm12 and emm1 in 2000s and 2010s. Hong Kong and Taiwan were dominated by emm12, emm4 and emm1, of which emm4 reduced but emm12 increased in 2010s significantly. From 1990 to 2020, newly found emm types were increasingly reported in various regions of China. The reported 30-valent M protein vaccine covered 26 M types prevalent in China, including all dominant types.

The rise and fall of acute rheumatic fever and rheumatic heart disease: a mini review

Introduction

The incidences of acute rheumatic fever (ARF) and rheumatic heart disease (RHD), which were leading causes of death in children in the 1920s, have decreased substantially. Considering the recent resurgence of scarlet fever and increased incidence of streptococcal pharyngitis in children, an investigation of the current status of ARF and RHD may be worthwhile.

Objective

To summarize the prevalence trends, pathogenic factors, and prevention strategies for ARF and RHD in children.

Methods

A selective search of literature published between January 1920 and February 2023 was done in PubMed, using the terms "acute rheumatic fever", "rheumatic heart disease", "group A Streptococcus", "pharyngitis", "pharyngeal tonsillitis", "scarlet fever", "impetigo", "obstructive sleep apnea syndrome" and "child".

Results

Overcrowded homes and inadequate sanitation led to recurrent group A streptococcal infection, and the causal relationship between group A streptococcal infection and ARF/RHD was well established. Streptococcal infectious diseases, such as group A streptococcal pharyngeal tonsillitis, SF, impetigo, and obstructive sleep apnea syndrome, were associated with the occurrence of ARF and RHD. ARF and RHD were still prevalent in young people of developing countries and economically poor populations of high-income countries. Universal disease registration systems were critical to locating disease outbreaks, tracking disease transmission, and identifying high-risk populations. Four-level prevention strategies were effective in reducing the incidence and mortality of ARF and RHD.

Conclusions

Registry and preventive measures for ARF and RHD should be strengthened in areas of dense population; poor sanitation; resurgence of SF; and high incidence of streptococcal pharyngitis, impetigo, and obstructive sleep apnea syndrome.

Epidemiology of Respiratory Infections during the COVID-19 Pandemic

To face the COVID-19 outbreak, a wide range of non-pharmaceutical interventions (NPIs) aimed at limiting the spread of the virus in communities, such as mask-wearing, hand hygiene, social distancing, travel restrictions, and school closures, were introduced in most countries. Thereafter, a significant reduction of new asymptomatic and symptomatic COVID-19 cases occurred, although there were differences between countries according to the type and duration of the NPIs. In addition, the COVID-19 pandemic has been accompanied by significant variations in the global incidence of diseases due to the most common non-SARS-CoV-2 respiratory viruses and some bacteria. In this narrative review, the epidemiology of the most common non-SARS-CoV-2 respiratory infections during the COVID-19 pandemic is detailed. Moreover, factors that could have had a role in modifying the traditional circulation of respiratory pathogens are discussed. A literature analysis shows that NPIs were the most important cause of the general reduction in the incidence of influenza and respiratory syncytial virus infection in the first year of the pandemic, although the different sensitivity of each virus to NPIs, the type and duration of measures used, as well as the interference among viruses may have played a role in modulating viral circulation. Reasons for the increase in the incidences of Streptococcus pneumoniae and group A Streptococcus infections seem strictly linked to immunity debt and the role played by NPIs in reducing viral infections and limiting bacterial superimposed infections. These results highlight the importance of NPIs during pandemics, the need to monitor the circulation of infectious agents that cause diseases similar to those caused by pandemic agents, and the need to make efforts to improve coverage with available vaccines.

A Novel CovS Variant Harbored by a Colonization Strain Reduces Streptococcus pyogenes Virulence

Streptococcus pyogenes, also known as group A Streptococcus, causes a wide variety of diseases ranging from mild noninvasive to severe invasive infections. To identify possible causes of colonization-to-invasive switches, we determined the genomic sequences of 10 isolates from five pairs each composed of an invasive strain and a carriage strain originating from five infectious clusters. Among them, one pair displayed a single-nucleotide difference in covS, encoding the sensor histidine kinase of the two-component CovRS system that controls the expression of 15% of the genome. In contrast to previously described cases where the invasive strains harbor nonfunctional CovS proteins, the carriage strain possessed the mutation covST115C, leading to the replacement of the tyrosine at position 39 by a histidine. The CovSY39H mutation affected the expression of the genes from the CovR regulon in a unique fashion. Genes usually overexpressed in covS mutant strains were underexpressed and vice versa. Furthermore, the covS mutant strain barely responded to the addition of the CovS-signaling compounds Mg2+ and LL-37. The variations in the accumulation of two virulence factors paralleled the transcription modifications. In addition, the covST115C mutant strain showed less survival than its wild-type counterpart in murine macrophages. Finally, in two murine models of infection, the covS mutant strain was less virulent than the wild-type strain. Our study suggests that the CovSY39H protein compromises CovS phosphatase activity and that this yields a noninvasive strain. IMPORTANCE Streptococcus pyogenes, also known as group A Streptococcus, causes a wide variety of diseases, leading to 517,000 deaths yearly. The two-component CovRS system, which responds to MgCl2 and the antimicrobial peptide LL-37, controls the expression of 15% of the genome. Invasive strains may harbor nonfunctional CovS sensor proteins that lead to the derepression of most virulence genes. We isolated a colonization strain that harbors a novel covS mutation. This mutant strain harbored a transcriptome profile opposite that of other covS mutant strains, barely responded to environmental signals, and was less virulent than the wild-type strain. This supports the importance of the derepression of the expression of most virulence genes, via mutations that impact the phosphorylation of the regulator CovR, for favoring S. pyogenes invasive infections.

Emerging Invasive Group A Streptococcus M1UK Lineage Detected by Allele-Specific PCR, England, 20201

Increasing reports of invasive Streptococcus pyogenes infections mandate surveillance for toxigenic lineage M1_UK. An allele-specific PCR was developed to distinguish M1_UK from other emm1 strains. The M1_UK lineage represented 91% of invasive emm1 isolates in England in 2020. Allele-specific PCR will permit surveillance for M1_UK without need for genome sequencing.

Genomic Characterization of Skin and Soft Tissue Streptococcus pyogenes Isolates from a Low-Income and a High-Income Setting

Streptococcus pyogenes is a leading cause of human morbidity and mortality, especially in resource-limited settings. The development of a vaccine against S. pyogenes is a global health priority to reduce the burden of postinfection rheumatic heart disease. To support this, molecular characterization of circulating S. pyogenes isolates is needed. We performed whole-genome analyses of S. pyogenes isolates from skin and soft tissue infections in Sukuta, The Gambia, a low-income country (LIC) in West Africa where there is a high burden of such infections. To act as a comparator to these LIC isolates, skin infection isolates from Sheffield, United Kingdom (a high-income country [HIC]), were also sequenced. The LIC isolates from The Gambia were genetically more diverse (46 emm types in 107 isolates) than the HIC isolates from Sheffield (23 emm types in 142 isolates), with only 7 overlapping emm types. Other molecular markers were shared, including a high prevalence of the skin infection-associated emm pattern D and the variable fibronectin-collagen-T antigen (FCT) types FCT-3 and FCT-4. Fewer of the Gambian LIC isolates carried prophage-associated superantigens (64%) and DNases (26%) than did the Sheffield HIC isolates (99% and 95%, respectively). We also identified streptococcin genes unique to 36% of the Gambian LIC isolates and a higher prevalence (48%) of glucuronic acid utilization pathway genes in the Gambian LIC isolates than in the Sheffield HIC isolates (26%). Comparison to a wider collection of HIC and LIC isolate genomes supported our findings of differing emm diversity and prevalence of bacterial factors. Our study provides insight into the genetics of LIC isolates and how they compare to HIC isolates. IMPORTANCE The global burden of rheumatic heart disease (RHD) has triggered a World Health Organization response to drive forward development of a vaccine against the causative human pathogen Streptococcus pyogenes. This burden stems primarily from low- and middle-income settings where there are high levels of S. pyogenes skin and soft tissue infections, which can lead to RHD. Our study provides much needed whole-genome-based molecular characterization of isolates causing skin infections in Sukuta, The Gambia, a low-income country (LIC) in West Africa where infection and RHD rates are high. Although we identified a greater level of diversity in these LIC isolates than in isolates from Sheffield, United Kingdom (a high-income country), there were some shared features. There were also some features that differed by geographical region, warranting further investigation into their contribution to infection. Our study has also contributed data essential for the development of a vaccine that would target geographically relevant strains.

Continued Increase of Erythromycin Nonsusceptibility and Clindamycin Nonsusceptibility Among Invasive Group A Streptococci Driven by Genomic Clusters, United States, 2018-2019

We analyzed 9630 invasive GAS surveillance isolates in the USA. From 2015-2017 to 2018-2019, significant increases in erythromycin-nonsusceptibility (18% vs 25%) and clindamycin-nonsusceptibility (17% vs 24%) occurred, driven by rapid expansions of genomic subclones. Prevention and control of clustered infections appear key to containing antimicrobial resistance.

The Shr receptor from Streptococcus pyogenes uses a cap and release mechanism to acquire heme-iron from human hemoglobin

Streptococcus pyogenes (group A Streptococcus) is a clinically important microbial pathogen that requires iron in order to proliferate. During infections, S. pyogenes uses the surface displayed Shr receptor to capture human hemoglobin (Hb) and acquires its iron-laden heme molecules. Through a poorly understood mechanism, Shr engages Hb via two structurally unique N-terminal Hb-interacting domains (HID1 and HID2) which facilitate heme transfer to proximal NEAr Transporter (NEAT) domains. Based on the results of X-ray crystallography, small angle X-ray scattering, NMR spectroscopy, native mass spectrometry, and heme transfer experiments, we propose that Shr utilizes a "cap and release" mechanism to gather heme from Hb. In the mechanism, Shr uses the HID1 and HID2 modules to preferentially recognize only heme-loaded forms of Hb by contacting the edges of its protoporphyrin rings. Heme transfer is enabled by significant receptor dynamics within the Shr-Hb complex which function to transiently uncap HID1 from the heme bound to Hb's β subunit, enabling the gated release of its relatively weakly bound heme molecule and subsequent capture by Shr's NEAT domains. These dynamics may maximize the efficiency of heme scavenging by S. pyogenes, enabling it to preferentially recognize and remove heme from only heme-loaded forms of Hb that contain iron.

The Development of Surface-Modified Liposomes as an Intranasal Delivery System for Group A Streptococcus Vaccines

Intranasal vaccine administration can overcome the disadvantages of injectable vaccines and present greater efficiency for mass immunization. However, the development of intranasal vaccines is challenged by poor mucosal immunogenicity of antigens and the limited availability of mucosal adjuvants. Here, we examined a number of self-adjuvanting liposomal systems for intranasal delivery of lipopeptide vaccine against group A Streptococcus (GAS). Among them, two liposome formulations bearing lipidated cell-penetrating peptide KALA and a new lipidated chitosan derivative (oleoyl-quaternized chitosan, OTMC) stimulated high systemic antibody titers in outbred mice. The antibodies were fully functional and were able to kill GAS bacteria. Importantly, OTMC was far more effective at stimulating antibody production than the classical immune-stimulating trimethyl chitosan formulation. In a simple physical mixture, OTMC also enhanced the immune responses of the tested vaccine, without the need for a liposome delivery system. The adjuvanting capacity of OTMC was further confirmed by its ability to stimulate cytokine production by dendritic cells. Thus, we discovered a new immune stimulant with promising properties for mucosal vaccine development.

The Cell Wall Deacetylases Spy1094 and Spy1370 Contribute to Streptococcus pyogenes Virulence

Streptococcus pyogenes, or Group A Streptococcus (GAS), is a strictly human pathogen that causes a wide range of diseases, including skin and soft tissue infections, toxic shock syndrome and acute rheumatic fever. We have recently reported that Spy1094 and Spy1370 of S. pyogenes serotype M1 are N-acetylglucosamine (GlcNAc) deacetylases. We have generated spy1094 and spy1370 gene deletion mutants in S. pyogenes and gain-of-function mutants in Lactococcus lactis. Similar to other cell wall deacetylases, our results show that Spy1094 and Spy1370 confer lysozyme-resistance. Furthermore, deletion of the genes decreased S. pyogenes virulence in a human whole blood killing assay and a Galleria mellonella (Greater wax moth) larvae infection model. Expression of the two genes in L. lactis resulted in increased lysozyme resistance and survival in whole human blood, and reduced survival of infected G. mellonella larvae. Deletion of the spy1370, but not the spy1094 gene, decreased resistance to the cationic antimicrobial peptide cecropin B, whereas both enzymes increased biofilm formation, probably resulting from the increase in positive charges due to deacetylation of the cell wall. In conclusion, Spy1094 and Spy1370 are important S. pyogenes virulence factors and might represent attractive targets for the development of antibacterial agents.

Should Linezolid Replace Clindamycin as the Adjunctive Antimicrobial of Choice in Group A Streptococcal Necrotizing Soft Tissue Infection and Toxic Shock Syndrome? A Focused Debate

Group A Streptococcus (GAS) necrotizing soft tissue infections and toxic shock syndrome remain high-mortality conditions. In vitro and animal model data, as well as multiple observational studies, suggest adjunctive clindamycin (ie, given with a beta-lactam) reduces invasive GAS infection mortality by inhibiting exotoxin production. Unfortunately, clindamycin resistance in GAS has been rapidly increasing in the United States since the mid-2010s, although the clinical significance of this remains unclear. Linezolid is a promising alternative adjunctive agent to which US GAS isolates remain near-universally susceptible, with a similar mechanism of action and similar in vitro evidence of GAS virulence factor attenuation. However, the clinical data supporting linezolid's value in severe GAS infections are far more limited. Here the authors review the data and reasoning behind a general preference for clindamycin or linezolid in a focused, pro-con debate format.

Rheumatic Heart Disease: JACC Focus Seminar 2/4

It is a sad reality that although eminently preventable, and despite possessing such knowledge for >70 years, rheumatic heart disease (RHD) remains the most common cause of cardiovascular morbidity and early mortality in young people worldwide. A disease of the poor, RHD is one of the most neglected diseases. Several challenges are unique to the acute rheumatic fever/RHD continuum and contribute to its persistence, including its sequestration among the poorest, its protracted natural history, the erratic availability of penicillin, and the lack of a concerted effort in endemic regions. However, there is cause for optimism following a resurgence in scientific interest over the last 15 years. This review presents the latest advancements in epidemiology, diagnosis, and management. It also discusses pressing research questions on disease pathophysiology, the barriers to implementation of effective management strategies, and pragmatic policy solutions required for translation of current knowledge into meaningful action.

The Bacterial Markers of Identification of Invasive CovR/CovS-Inactivated Group A Streptococcus

Necrotizing fasciitis is a severe infectious disease that results in significant mortality. Streptococcus pyogenes (group A Streptococcus, GAS) is one of the most common bacterial pathogens of monomicrobial necrotizing fasciitis. The early diagnosis of necrotizing fasciitis is crucial; however, the typical cutaneous manifestations are not always presented in patients with GAS necrotizing fasciitis, which would lead to miss- or delayed diagnosis. GAS with spontaneous inactivating mutations in the CovR/CovS two-component regulatory system is significantly associated with destructive diseases such as necrotizing fasciitis and toxic shock syndrome; however, no specific marker has been used to identify these invasive clinical isolates. This study evaluated the sensitivity and specificity of using CovR/CovS-controlled phenotypes to identify CovR/CovS-inactivated isolates. Results showed that the increase of hyaluronic acid capsule production and streptolysin O expression were not consistently presented in CovS-inactivated clinical isolates. The repression of SpeB is the phenotype with 100% sensitivity of identifying in CovS-inactivated isolates among 61 clinical isolates. Nonetheless, this phenotype failed to distinguish RopB-inactivated isolates from CovS-inactivated isolates and cannot be utilized to identify CovR-inactivated mutant and RocA (Regulator of Cov)-inactivated isolates. In this study, we identified and verified that PepO, the endopeptidase which regulates SpeB expression through degrading SpeB-inducing quorum-sensing peptide, was a bacterial marker to identify isolates with defects in the CovR/CovS pathway. These results also inform the potential strategy of developing rapid detection methods to identify invasive GAS variants during infection. IMPORTANCE Necrotizing fasciitis is rapidly progressive and life-threatening; if the initial diagnosis is delayed, deep soft tissue infection can progress to massive tissue destruction and toxic shock syndrome. Group A Streptococcus (GAS) with inactivated mutations in the CovR/CovS two-component regulatory system are related to necrotizing fasciitis and toxic shock syndrome; however, no bacterial marker is available to identify these invasive clinical isolates. Inactivation of CovR/CovS resulted in the increased expression of endopeptidase PepO. Our study showed that the upregulation of PepO mediates a decrease in SpeB-inducing peptide (SIP) in the covR mutant, indicating that CovR/CovS modulates SIP-dependent quorum-sensing activity through PepO. Importantly, the sensitivity and specificity of utilizing PepO to identify clinical isolates with defects in the CovR/CovS pathway, including its upstream RocA regulator, were 100%. Our results suggest that identification of invasive GAS by PepO may be a strategy for preventing severe manifestation or poor prognosis after GAS infection.

Increasing Incidence of Invasive Group A Streptococcus Disease, Idaho, USA, 2008-2019

We investigated invasive group A Streptococcus epidemiology in Idaho, USA, during 2008–2019 using surveillance data, medical record review, and emm (M protein gene) typing results. Incidence increased from 1.04 to 4.76 cases/100,000 persons during 2008–2019. emm 1, 12, 28, 11, and 4 were the most common types, and 2 outbreaks were identified. We examined changes in distribution of clinical syndrome, patient demographics, and risk factors by comparing 2008–2013 baseline with 2014–2019 data. Incidence was higher among all age groups during 2014–2019. Streptococcal toxic shock syndrome increased from 0% to 6.4% of cases (p = 0.02). We identified no differences in distribution of demographic or risk factors between periods. Results indicated that invasive group A Streptococcus is increasing among the general population of Idaho. Ongoing surveillance of state-level invasive group A Streptococcus cases could help identify outbreaks, track regional trends in incidence, and monitor circulating emm types.

Health-Economic Value of Vaccination Against Group A Streptococcus in the United States

BACKGROUND

Vaccines are needed to reduce the burden of group A Streptococcus (GAS). We assessed the potential health-economic value of GAS vaccines achievable through prevention of invasive disease and acute upper respiratory infections in the United States.

METHODS

We estimated annual incidence of invasive GAS disease and associated costs incurred from hospitalization and management of long-term sequelae, as well as productivity losses resulting from acute illness, long-term disability, and mortality. We also estimated healthcare and productivity costs associated with GAS pharyngitis, sinusitis, and acute otitis media. We estimated costs averted by prevention of invasive disease and acute upper respiratory infections for vaccines with differing efficacy profiles; our base case considered vaccines meeting the World Health Organization Preferred Product Profile (WHO-PPP) with a 6-year average duration of protection.

RESULTS

Costs of invasive GAS disease and acute upper respiratory infections totaled $6.08 (95% confidence interval [CI], $5.33-$6.86) billion annually. Direct effects of vaccines meeting WHO-PPP characteristics and administered at ages 12 and 18 months would avert $609 (95% CI, $558-$663) million in costs annually, primarily by preventing noninvasive disease; with an additional dose at age 5 years, averted costs would total $869 (95% CI, $798-$945) million annually. Adult vaccination at age 65 years would avert $326 (95% CI, $271-$387) million in annual costs associated with invasive GAS disease. Indirect effects of vaccination programs reducing incidence of GAS diseases across all ages by 20% would avert roughly $1 billion in costs each year.

CONCLUSIONS

The economic burden of GAS is substantial. Our findings should inform prioritization of GAS vaccine development and evaluation.

Genomic analysis of group A Streptococcus isolated during a correctional facility outbreak of MRSA in 2004

BACKGROUND

In 2004-2005, an outbreak of impetigo occurred at a correctional facility during a sentinel outbreak of methicillin- resistant Staphylococcus aureus (MRSA) in Alberta, Canada. Next-generation sequencing (NGS) was used to characterize the group A Streptococcus (GAS) isolates and evaluate whether genomic biomarkers could distinguish between those recovered alone and those co-isolated with S. aureus.

METHODS

Superficial wound swabs collected from all adults with impetigo during this outbreak were cultured using standard methods. NGS was used to characterize and compare all of the GAS and S. aureus genomes.

RESULTS

Fifty-three adults were culture positive for GAS, with a subset of specimens also positive for MRSA (n = 5) or methicillin-sensitive S. aureus (n = 3). Seventeen additional MRSA isolates from this facility from the same time frame (no GAS co-isolates) were also included. All 78 bacterial genomes were analyzed for the presence of known virulence factors, plasmids, and antimicrobial resistance (AMR) genes. Among the GAS isolates were 12 emm types, the most common being 41.2 (n = 27; 51%). GAS genomes were phylogenetically compared with local and public datasets of invasive and non-invasive isolates. GAS genomes had diverse profiles for virulence factors, plasmids, and AMR genes. Pangenome analysis did not identify horizontally transferred genes in the co-infection versus single infections.

CONCLUSIONS

GAS recovered from invasive and non-invasive sources were not genetically distinguishable. Virulence factors, plasmids, and AMR profiles grouped by emm type, and no genetic changes were identified that predict co-infection or horizontal gene transfer between GAS and S. aureus.

Structure-activity relationship of lipid, cyclic peptide and antigen rearrangement of physically mixed vaccines

Currently there is no approved vaccine to prevent and/or treat group A Streptococcus (GAS) infection. With increasing reports of GAS antibiotic resistance, vaccine adjuvants and targeted delivery systems which induce a strong immune response are a widely acknowledged unmet need. Through extensive structure-activity studies, we investigated a cyclic decapeptide physically mixed with a GAS B cell peptide epitope (J8), a universal T helper epitope (PADRE), and different synthetic lipidic moieties as a conceivable self-adjuvanting GAS vaccine. We explored the structure (orientation)-relationship of the chemically-conjugated B cell epitope and T helper epitope peptide as part of this physically-mixed vaccine. Following in vivo assessment in mice, these cyclic lipopeptide vaccines showed successful induction of J8-specific systemic IgG antibodies when administered subcutaneously without additional adjuvant. Interestingly, an exposed C-terminus of the GAS B cell epitope and a 16-carbon alpha-amino fatty acid lipid was required for strong immunoreactivity, capable of effectively opsonising multiple strains of clinically-isolated GAS bacteria. Physicochemical assessment proved the alpha helix structure of the GAS B cell epitope was retained, impacting particle self-assembly and vaccine immunoreactivity. This study showed the capability for a self-adjuvanting cyclic delivery system to act as a vehicle for the delivery of GAS peptide antigens to treat GAS infection.

Serological Profiling of Group A Streptococcus Infections in Acute Rheumatic Fever

Rheumatic fever is a serious post-infectious sequela of group A Streptococcus (GAS). Prior GAS exposures were mapped in sera using a large panel of M-type specific peptides. Rheumatic fever patients had serological evidence of significantly more GAS exposures than matched controls suggesting immune priming by repeat infections contributes to pathogenesis.

Identification of epidemic scarlet fever group A Streptococcus strains in the paediatric population of Houston, TX, USA

Scarlet fever (SF) has recently been associated with group A streptococcal (GAS) strains possessing multidrug resistance and specific streptococcal exotoxins. We screened a local surveillance collection of GAS emm12 strains in Houston, TX, USA for antimicrobial resistance and identified a single isolate matching the antimicrobial resistance pattern previously reported for SF clones. Using whole-genome sequencing and combining genome sequence data derived from national surveillance databases, we identified additional emm12 GAS clones similar to those associated with prior SF outbreaks, emphasizing the need for continued surveillance for epidemic emergence in the USA.

Antibiotic Treatment, Mechanisms for Failure, and Adjunctive Therapies for Infections by Group A Streptococcus

Group A Streptococcus (GAS; Streptococcus pyogenes) is a nearly ubiquitous human pathogen responsible for a significant global disease burden. No vaccine exists, so antibiotics are essential for effective treatment. Despite a lower incidence of antimicrobial resistance than many pathogens, GAS is still a top 10 cause of death due to infections worldwide. The morbidity and mortality are primarily a consequence of the immune sequelae and invasive infections that are difficult to treat with antibiotics. GAS has remained susceptible to penicillin and other β-lactams, despite their widespread use for 80 years. However, the failure of treatment for invasive infections with penicillin has been consistently reported since the introduction of antibiotics, and strains with reduced susceptibility to β-lactams have emerged. Furthermore, isolates responsible for outbreaks of severe infections are increasingly resistant to other antibiotics of choice, such as clindamycin and macrolides. This review focuses on the challenges in the treatment of GAS infection, the mechanisms that contribute to antibiotic failure, and adjunctive therapeutics. Further understanding of these processes will be necessary for improving the treatment of high-risk GAS infections and surveillance for non-susceptible or resistant isolates. These insights will also help guide treatments against other leading pathogens for which conventional antibiotic strategies are increasingly failing.

Evaluating the Diagnostic Paradigm for Group A and Non-Group A Streptococcal Pharyngitis in the College Student Population

Background

Acute pharyngitis is a frequent illness presenting in outpatient settings. Antibiotics are only recommended for bacterial pharyngitis caused by group A β-hemolytic streptococci (GAS); however, infections with non-group A β-hemolytic streptococci (NGAS) have similar clinical presentations and are common in young adult populations. The objective of this study was to analyze the performance of a current (expert) diagnostic algorithm for GAS pharyngitis, the Centor score, and compare it to alternative models developed to predict GAS and NGAS in a college student population.

Methods

Electronic health records were obtained for all patients who received a streptococcal rapid antigen detection test (RADT) and/or a bacterial throat culture (n = 3963) at a southeastern US university in 2014. Bivariate and multivariable regression models (least absolute shrinkage and selection operator [LASSO] and stepwise-selected) were fitted to assess and compare their diagnostic performances for GAS-positive and NGAS-positive infections.

Results

Prevalence of GAS was 18.8%. In the subset of RADT-negative patients who received bacterial throat cultures (n = 313), growth of NGAS occurred in 34.8%, with group C streptococci the most frequent isolate. Mean Centor score was higher for NGAS (3.2) vs GAS (2.9) infections (P = .0111). The area under the curve (AUC) for GAS prediction was 0.64 using the Centor score and 0.70 using the LASSO model. For NGAS, the most important features were cough, pharyngeal erythema, tonsillar exudate, and gastrointestinal symptoms (AUC = 0.63).

Conclusions

GAS and NGAS pharyngitis were indistinguishable among college students in this study utilizing a commonly applied decision score. Alternative models using additional clinical criteria may be useful for supporting diagnosis of this common illness.

The Utility of Rapid Group A Streptococcus Molecular Testing Compared with Throat Culture for the Diagnosis of Group A Streptococcal Pharyngitis in a High-Incidence Rheumatic Fever Population

Group A streptococcus (GAS) causes significant morbidity and mortality in New Zealand and is responsible for invasive disease and immune sequelae, including acute rheumatic fever (ARF). Early treatment of GAS pharyngitis reduces the risk of ARF. In settings with a high burden of GAS disease, a rapid GAS pharyngitis diagnostic test with a strong negative predictive value is needed to enable prompt and accurate treatment. This prospective study compares the Xpert Xpress Strep A molecular test (Cepheid) to throat culture and a second molecular method, the BioGX group A streptococcus-open system reagent (OSR) for BD Max for the diagnosis of GAS pharyngitis. Throat swabs were collected from the emergency department and wards of Middlemore Hospital, New Zealand. The BioGX group A streptococcus OSR for BD Max contributes to the composite gold standard of throat culture or both molecular methods positive. Basic demographic, clinical, and laboratory data were collected. Two hundred five out of two hundred fourteen swabs were suitable for analysis. Of those, 28/205 (13.7%) were GAS culture positive, 45/205 (22%) Xpert Xpress Strep A positive, and 38/205 (18.5%) BioGX positive. Compared to culture, the sensitivity, specificity, and positive and negative predictive values of the Xpert Xpress Strep A molecular test were 100%, 90.4%, 62.2%, and 100%, respectively. Compared to the composite gold standard, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 100%, 95.8%, 84.4%, and 100%, respectively. Seventeen samples were Xpert Xpress positive but culture negative; 6 of these 17 swabs represent true positives with evidence of recent GAS infection. Ten samples were culture negative but both Xpert Xpress and BioGX positive. The Xpert Xpress Strep A molecular test is highly sensitive with a strong negative predictive value and rapid turnaround time. It can be safely introduced as a first-line test for throat swabs in a high-incidence ARF population.

Isolation of Group A Streptococci with Reduced In Vitro β-Lactam Susceptibility Harboring Amino Acid Substitutions in Penicillin-Binding Proteins in Japan

Streptococcus pyogenes (group A Streptococcus [GAS]) has long been regarded as being susceptible to β-lactams. However, amino acid substitutions in penicillin-binding protein 2X (PBP2X) conferring reduced in vitro β-lactam susceptibility have been indicated since 2019 in the United States and Iceland. Here, we report the first isolation of Streptococcus pyogenes possessing the PBP2X substitution conferring reduced in vitro β-lactam susceptibility in Asia; however, the MICs were below the susceptible breakpoint of the CLSI.

Immunobiology of the Classical Lancefield Group A Streptococcal Carbohydrate Antigen

Group A Streptococcus (GAS) is a preeminent human bacterial pathogen causing hundreds of millions of infections each year worldwide. In the clinical setting, the bacterium is easily identified by a rapid antigen test against the group A carbohydrate (GAC), a polysaccharide that comprises 30 to 50% of the GAS cell wall by weight. Originally described by Rebecca Lancefield in the 1930s, GAC consists of a polyrhamnose backbone and a N-acetylglucosamine (GlcNAc) side chain. This side chain, the species-defining immunodominant antigen, is potentially implicated in autoreactive immune responses against human heart or brain tissue in poststreptococcal rheumatic fever or rheumatic heart disease. The recent discovery of the genetic locus encoding GAC biosynthesis and new insights into its chemical structure have provided novel insights into the assembly of the polysaccharide, its contribution to immune evasion and virulence, and ideas for safely harnessing its natural immunogenicity in vaccine design. This minireview serves to summarize the emerging new literature on GAC, the eponymous cell well antigen that provides structural integrity to GAS and directly interfaces with host innate and adaptive immune responses.