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Since 2014, England has seen increased scarlet fever activity unprecedented in modern times. In 2016, England's scarlet fever seasonal rise coincided with an unexpected elevation in invasive Streptococcus pyogenes infections. We describe the molecular epidemiological investigation of these events. We analysed changes in S pyogenes emm genotypes, and notifications of scarlet fever and invasive disease in 2014–16 using regional (northwest London) and national (England and Wales) data. Genomes of 135 non-invasive and 552 invasive emm1 isolates from 2009–16 were analysed and compared with 2800 global emm1 sequences. Transcript and protein expression of streptococcal pyrogenic exotoxin A (SpeA; also known as scarlet fever or erythrogenic toxin A) in sequenced, non-invasive emm1 isolates was quantified by real-time PCR and western blot analyses. Coincident with national increases in scarlet fever and invasive disease notifications, emm1 S pyogenes upper respiratory tract isolates increased significantly in northwest London in the March to May period, from five (5%) of 96 isolates in 2014, to 28 (19%) of 147 isolates in 2015 (p=0·0021 vs 2014 values), to 47 (33%) of 144 in 2016 (p=0·0080 vs 2015 values). Similarly, invasive emm1 isolates collected nationally in the same period increased from 183 (31%) of 587 in 2015 to 267 (42%) of 637 in 2016 (p<0·0001). Sequences of emm1 isolates from 2009–16 showed emergence of a new emm1 lineage (designated M1UK)—with overlap of pharyngitis, scarlet fever, and invasive M1UK strains—which could be genotypically distinguished from pandemic emm1 isolates (M1global) by 27 single-nucleotide polymorphisms. Median SpeA protein concentration in supernatant was nine-times higher among M1UK isolates (190·2 ng/mL [IQR 168·9–200·4]; n=10) than M1global isolates (20·9 ng/mL [0·0–27·3]; n=10; p<0·0001). M1UK expanded nationally to represent 252 (84%) of all 299 emm1 genomes in 2016. Phylogenetic analysis of published datasets identified single M1UK isolates in Denmark and the USA. A dominant new emm1 S pyogenes lineage characterised by increased SpeA production has emerged during increased S pyogenes activity in England. The expanded reservoir of M1UK and recognised invasive potential of emm1 S pyogenes provide plausible explanation for the increased incidence of invasive disease, and rationale for global surveillance. UK Medical Research Council, UK National Institute for Health Research, Wellcome Trust, Rosetrees Trust, Stoneygate Trust.

Streptococcus pyogenes , or Group A Streptococcus (GAS), is a human pathogen responsible for a range of diseases, from mild infections to severe illnesses. Despite its significance in modern clinical settings, little is known about the pathogen’s evolutionary history or its presence in ancient human populations. Here, we present genomic evidence of S. pyogenes in the pre-Columbian Americas. We analysed a tooth from a naturally mummified individual dating to the Late Intermediate Period (1283–1383 cal AD), housed in the National Museum of Archeology (MUNARQ) in La Paz, Bolivia. Mitochondrial DNA analysis confirmed the host’s Native American ancestry. Shotgun metagenomic sequencing and de-novo assembly enabled the near-complete reconstruction of an ancient S. pyogenes genome displaying close similarity to contemporary strains linked to pharyngitis. The genome contains core virulence genes, but prophages lack streptococcal pyrogenic exotoxins. Phylogenetic analyses place the strain at the base of modern S. pyogenes diversity, and Bayesian analyses indicate that most extant lineages diversified globally within the past ~5,500 years. Our results push back the confirmed presence of S. pyogenes in the Americas by several centuries and suggest that the pathogen circulated among Indigenous populations prior to the European contact. Streptococcus pyogenes is a human pathogen responsible for a range of diseases. Here, the authors reconstruct an ancient S. pyogenes genome from a pre-Columbian Bolivian mummy, supporting that the pathogen circulated in the Americas prior to the European contact.

Recent advances in the scale and diversity of population genomic datasets for bacteria now provide the potential for genome-wide patterns of co-evolution to be studied at the resolution of individual bases. Here we describe a new statistical method, genomeDCA, which uses recent advances in computational structural biology to identify the polymorphic loci under the strongest co-evolutionary pressures. We apply genomeDCA to two large population data sets representing the major human pathogens Streptococcus pneumoniae (pneumococcus) and Streptococcus pyogenes (group A Streptococcus). For pneumococcus we identified 5,199 putative epistatic interactions between 1,936 sites. Over three-quarters of the links were between sites within the pbp2x, pbp1a and pbp2b genes, the sequences of which are critical in determining non-susceptibility to beta-lactam antibiotics. A network-based analysis found these genes were also coupled to that encoding dihydrofolate reductase, changes to which underlie trimethoprim resistance. Distinct from these antibiotic resistance genes, a large network component of 384 protein coding sequences encompassed many genes critical in basic cellular functions, while another distinct component included genes associated with virulence. The group A Streptococcus (GAS) data set population represents a clonal population with relatively little genetic variation and a high level of linkage disequilibrium across the genome. Despite this, we were able to pinpoint two RNA pseudouridine synthases, which were each strongly linked to a separate set of loci across the chromosome, representing biologically plausible targets of co-selection. The population genomic analysis method applied here identifies statistically significantly co-evolving locus pairs, potentially arising from fitness selection interdependence reflecting underlying protein-protein interactions, or genes whose product activities contribute to the same phenotype. This discovery approach greatly enhances the future potential of epistasis analysis for systems biology, and can complement genome-wide association studies as a means of formulating hypotheses for targeted experimental work.

Abstract Group A Streptococcus (GAS) has recently reemerged as a leading cause of both mild and severe invasive infections worldwide, with recent upsurges in invasive disease among children and adults. Notwithstanding a partial synchronicity with the COVID-19 pandemic, this rapid global dissemination of more virulent GAS lineages has been promptly detected, as well as the molecular shifts underlying the observed changes in clinical patterns. Whole-genome sequencing (WGS)-based genomic epidemiology allowed us to gain relevant insights into this upsurge as it was happening. This review integrates the canonical research publication-based approach with genomic data and metadata and identifies a subset of genomic clusters playing a major role in invasive GAS (iGAS) infections worldwide, which were named as Global Pathogenic Lineages (GPLs). The four GPLs broadly coincide with five sequence types (STs): GPL1 with ST28, GPL2 with ST15 and ST315, GPL3 with ST52, and GPL4 with ST39. While non-GPLs clusters maintain a baseline reservoir of antimicrobial‐resistance and virulence genes, GPLs show varying but noteworthy resistance profiles and are frequent causes of iGAS. The integration of WGS into routine diagnostics procedures is a forthcoming improvement, aimed not only at informing tailored therapy and implementing infection control strategies, but also to perform continuous surveillance. Ongoing WGS in clinical microbiology, as a matter of fact, will provide unparalleled insights into lineage emergence, transmission dynamics, and the geographic clustering of virulence and resistance determinants. Group A Streptococcus dramatically reemerged as a leading cause of both mild and severe invasive infections worldwide, spurred by more virulent lineages whose rapid global dissemination manifested with a shift in clinical patterns, and this review combining Whole-genome sequencing data and scientific literature defines the main virulence determinants and novel emerging lineages.

Key Points Streptococcus pyogenes , also called group A Streptococcus (GAS), is a Gram-positive bacterial pathogen that naturally infects only humans and is the aetiological agent of several potentially fatal syndromes, including 'flesh-eating disease' (necrotizing fasciitis). The worldwide resurgence of severe invasive GAS infections over the past 30 years is correlated with the global dissemination of the GAS serotype M1T1 clone. Recent work demonstrates that the capacity of GAS serotype M1T1 to cause invasive disease is increased by selection for mutations within the covRS two-component regulator operon. This genetic alteration dramatically changes the transcriptome, resulting in the downregulation of a broad-spectrum cysteine protease, streptococcal pyrogenic exotoxin B (SpeB), and the upregulation of several virulence factors, including the nuclease extracellular streptodornase D (Sda1). Elevated Sda1 nuclease activity enhances the resistance of GAS serotype M1T1 to neutrophil-mediated killing, through the degradation of DNA-based neutrophil extracellular traps, and the absence of SpeB protease activity permits the accumulation of plasmin activity on the GAS cell surface, triggering tissue destruction and systemic spread. GAS uses a repertoire of virulence factors to thwart the host innate immune response, and several of these factors are critical for invasive disease. The switch from non-invasive to hyperinvasive GAS is triggered by particular genetic events, and our increased understanding of this switch has led to a model for the initiation of invasive GAS disease in humans. An understanding of the mechanism by which GAS causes serious invasive infections may augment the development of new-generation therapeutics and provide better health outcomes in the fight against this globally important human pathogen. Group A Streptococcus can cause devastating infections with high mortality rates. Here, Walker and colleagues describe the bacterial virulence factors that allow this species to infect tissues and escape destruction in neutrophils, and discuss how genetic changes in a two-component regulatory system promote pathogenicity. Streptococcus pyogenes is also known as group A Streptococcus (GAS) and is an important human pathogen that causes considerable morbidity and mortality worldwide. The GAS serotype M1T1 clone is the most frequently isolated serotype from life-threatening invasive (at a sterile site) infections, such as streptococcal toxic shock-like syndrome and necrotizing fasciitis. Here, we describe the virulence factors and newly discovered molecular events that mediate the in vivo changes from non-invasive GAS serotype M1T1 to the invasive phenotype, and review the invasive-disease trigger for non-M1 GAS. Understanding the molecular basis and mechanism of initiation for streptococcal invasive disease may expedite the discovery of novel therapeutic targets for the treatment and control of severe invasive GAS diseases.

The re-emergence of scarlet fever poses a new global public health threat. The capacity of North-East Asian serotype M12 ( emm 12) Streptococcus pyogenes (group A Streptococcus , GAS) to cause scarlet fever has been linked epidemiologically to the presence of novel prophages, including prophage ΦHKU.vir encoding the secreted superantigens SSA and SpeC and the DNase Spd1. Here, we report the molecular characterization of ΦHKU.vir-encoded exotoxins. We demonstrate that streptolysin O (SLO)-induced glutathione efflux from host cellular stores is a previously unappreciated GAS virulence mechanism that promotes SSA release and activity, representing the first description of a thiol-activated bacterial superantigen. Spd1 is required for resistance to neutrophil killing. Investigating single, double and triple isogenic knockout mutants of the ΦHKU.vir-encoded exotoxins, we find that SpeC and Spd1 act synergistically to facilitate nasopharyngeal colonization in a mouse model. These results offer insight into the pathogenesis of scarlet fever-causing GAS mediated by prophage ΦHKU.vir exotoxins. The pathogenesis of Streptococcus pyogenes (GAS) causing scarlet fever has been associated with the presence of prophages, such as ΦHKU.vir, and their products. Here, the authors characterize the exotoxins SpeC and Spd1 of ΦHKU.vir and show these to act synergistically to facilitate nasopharyngeal colonization in mice.

Group A streptococci (GAS) are genetically diverse. Determination of strain features can reveal associations with disease and resistance and assist in vaccine formulation. We employed whole-genome sequence (WGS)-based characterization of 1,454 invasive GAS isolates recovered in 2015 by Active Bacterial Core Surveillance and performed conventional antimicrobial susceptibility testing. Predictions were made for genotype, GAS carbohydrate, antimicrobial resistance, surface proteins (M family, fibronectin binding, T, R28), secreted virulence proteins (Sda1, Sic, exotoxins), hyaluronate capsule, and an upregulated nga operon (encodes NADase and streptolysin O) promoter (Pnga3). Sixty-four M protein gene ( emm ) types were identified among 69 clonal complexes (CCs), including one CC of Streptococcus dysgalactiae subsp. equisimilis . emm types predicted the presence or absence of active sof determinants and were segregated into sof- positive or sof- negative genetic complexes. Only one “ emm type switch” between strains was apparent. sof -negative strains showed a propensity to cause infections in the first quarter of the year, while sof + strain infections were more likely in summer. Of 1,454 isolates, 808 (55.6%) were Pnga3 positive and 637 (78.9%) were accounted for by types emm1 , emm89 , and emm12 . Theoretical coverage of a 30-valent M vaccine combined with an M-related protein (Mrp) vaccine encompassed 98% of the isolates. WGS data predicted that 15.3, 13.8, 12.7, and 0.6% of the isolates were nonsusceptible to tetracycline, erythromycin plus clindamycin, erythromycin, and fluoroquinolones, respectively, with only 19 discordant phenotypic results. Close phylogenetic clustering of emm59 isolates was consistent with recent regional emergence. This study revealed strain traits informative for GAS disease incidence tracking, outbreak detection, vaccine strategy, and antimicrobial therapy. IMPORTANCE The current population-based WGS data from GAS strains causing invasive disease in the United States provide insights important for prevention and control strategies. Strain distribution data support recently proposed multivalent M type-specific and conserved M-like protein vaccine formulations that could potentially protect against nearly all invasive U.S. strains. The three most prevalent clonal complexes share key polymorphisms in the nga operon encoding two secreted virulence factors (NADase and streptolysin O) that have been previously associated with high strain virulence and transmissibility. We find that Streptococcus pyogenes is phylogenetically subdivided into loosely defined multilocus sequence type-based clusters consisting of solely sof- negative or sof- positive strains; with sof- negative strains demonstrating differential seasonal preference for infection, consistent with the recently demonstrated differential seasonal preference based on phylogenetic clustering of full-length M proteins. This might relate to the differences in GAS strain compositions found in different geographic settings and could further inform prevention strategies. The current population-based WGS data from GAS strains causing invasive disease in the United States provide insights important for prevention and control strategies. Strain distribution data support recently proposed multivalent M type-specific and conserved M-like protein vaccine formulations that could potentially protect against nearly all invasive U.S. strains. The three most prevalent clonal complexes share key polymorphisms in the nga operon encoding two secreted virulence factors (NADase and streptolysin O) that have been previously associated with high strain virulence and transmissibility. We find that Streptococcus pyogenes is phylogenetically subdivided into loosely defined multilocus sequence type-based clusters consisting of solely sof- negative or sof- positive strains; with sof- negative strains demonstrating differential seasonal preference for infection, consistent with the recently demonstrated differential seasonal preference based on phylogenetic clustering of full-length M proteins. This might relate to the differences in GAS strain compositions found in different geographic settings and could further inform prevention strategies.

To determine invasive group A Streptococcus trends in Canada, we characterized emm1 isolates collected during 2018-2023. The percentage of hypervirulent M1 lineage isolates increased significantly, from 22.1% in 2018 to 60.2% in 2023. Genomic analysis identified geographically and temporally associated clusters and genes associated with virulent bacteriophage acquisition.

We sequenced the genomes of 3,615 strains of serotype Emm protein 1 (M1) group A Streptococcus to unravel the nature and timing of molecular events contributing to the emergence, dissemination, and genetic diversification of an unusually virulent clone that now causes epidemic human infections worldwide. We discovered that the contemporary epidemic clone emerged in stepwise fashion from a precursor cell that first contained the phage encoding an extracellular DNase virulence factor (streptococcal DNase D2, SdaD2) and subsequently acquired the phage encoding the SpeA1 variant of the streptococcal pyrogenic exotoxin A superantigen. The SpeA2 toxin variant evolved from SpeA1 by a single-nucleotide change in the M1 progenitor strain before acquisition by horizontal gene transfer of a large chromosomal region encoding secreted toxins NAD ⁺-glycohydrolase and streptolysin O. Acquisition of this 36-kb region in the early 1980s into just one cell containing the phage-encoded sdaD2 and speA2 genes was the final major molecular event preceding the emergence and rapid intercontinental spread of the contemporary epidemic clone. Thus, we resolve a decades-old controversy about the type and sequence of genomic alterations that produced this explosive epidemic. Analysis of comprehensive, population-based contemporary invasive strains from seven countries identified strong patterns of temporal population structure. Compared with a preepidemic reference strain, the contemporary clone is significantly more virulent in nonhuman primate models of pharyngitis and necrotizing fasciitis. A key finding is that the molecular evolutionary events transpiring in just one bacterial cell ultimately have produced millions of human infections worldwide.

During the late phase of the COVID-19 pandemic, several high-income countries reported a surge in invasive group A streptococcal (iGAS) infections, with notable paediatric morbidity and mortality. This Review explores three potential drivers of this increase: the role of the COVID-19 pandemic and associated non-pharmaceutical interventions on group A streptococcus (GAS) circulation; the potential burden associated with other respiratory viruses such as influenza and respiratory syncytial virus; and the potential role of hypervirulent GAS clones and lineages. The resurgence of iGAS disease highlights the need for enhanced surveillance of both invasive and non-invasive GAS infections, as well as further research to clarify the role of immunity, viral interactions, and bacterial molecular epidemiology and its evolution. A comprehensive understanding of these dynamics is essential to inform future public health strategies aimed at mitigating the burden of iGAS disease.