A naturally occurring mutation in ropB suppresses SpeB expression and reduces M1T1 group A streptococcal systemic virulence

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

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

Streptococcal peptides and their roles in host-microbe interactions

The genus Streptococcus encompasses many bacterial species that are associated with hosts, ranging from asymptomatic colonizers and commensals to pathogens with a significant global health burden. Streptococci produce numerous factors that enable them to occupy their host-associated niches, many of which alter their host environment to the benefit of the bacteria. The ability to manipulate host immune systems to either evade detection and clearance or induce a hyperinflammatory state influences whether bacteria are able to survive and persist in a given environment, while also influencing the propensity of the bacteria to cause disease. Several bacterial factors that contribute to this inter-species interaction have been identified. Recently, small peptides have become increasingly appreciated as factors that contribute to Streptococcal relationships with their hosts. Peptides are utilized by streptococci to modulate their host environment in several ways, including by directly interacting with host factors to disrupt immune system function and signaling to other bacteria to control the expression of genes that contribute to immune modulation. In this review, we discuss the many contributions of Streptococcal peptides in terms of their ability to contribute to pathogenesis and disruption of host immunity. This discussion will highlight the importance of continuing to elucidate the functions of these Streptococcal peptides and pursuing the identification of new peptides that contribute to modulation of host environments. Developing a greater understanding of how bacteria interact with their hosts has the potential to enable the development of techniques to inhibit these peptides as therapeutic approaches against Streptococcal infections.

Neutrophil-derived reactive agents induce a transient SpeB negative phenotype in Streptococcus pyogenes

BACKGROUND

Streptococcus pyogenes (group A streptococci; GAS) is the main causative pathogen of monomicrobial necrotizing soft tissue infections (NSTIs). To resist immuno-clearance, GAS adapt their genetic information and/or phenotype to the surrounding environment. Hyper-virulent streptococcal pyrogenic exotoxin B (SpeB) negative variants caused by covRS mutations are enriched during infection. A key driving force for this process is the bacterial Sda1 DNase.

METHODS

Bacterial infiltration, immune cell influx, tissue necrosis and inflammation in patient´s biopsies were determined using immunohistochemistry. SpeB secretion and activity by GAS post infections or challenges with reactive agents were determined via Western blot or casein agar and proteolytic activity assays, respectively. Proteome of GAS single colonies and neutrophil secretome were profiled, using mass spectrometry.

RESULTS

Here, we identify another strategy resulting in SpeB-negative variants, namely reversible abrogation of SpeB secretion triggered by neutrophil effector molecules. Analysis of NSTI patient tissue biopsies revealed that tissue inflammation, neutrophil influx, and degranulation positively correlate with increasing frequency of SpeB-negative GAS clones. Using single colony proteomics, we show that GAS isolated directly from tissue express but do not secrete SpeB. Once the tissue pressure is lifted, GAS regain SpeB secreting function. Neutrophils were identified as the main immune cells responsible for the observed phenotype. Subsequent analyses identified hydrogen peroxide and hypochlorous acid as reactive agents driving this phenotypic GAS adaptation to the tissue environment. SpeB-negative GAS show improved survival within neutrophils and induce increased degranulation.

CONCLUSIONS

Our findings provide new information about GAS fitness and heterogeneity in the soft tissue milieu and provide new potential targets for therapeutic intervention in NSTIs.

The Anti-Biofilm Potential of Linalool, a Major Compound from Hedychium larsenii, against Streptococcus pyogenes and Its Toxicity Assessment in Danio rerio

The anti-biofilm and anti-virulence potential of the essential oil (E.O.) extracted from Hedychium larsenii M. Dan & Sathish was determined against Streptococcus pyogenes. A crystal violet assay was employed to quantify the biofilm. Linalool, a monoterpene alcohol from the E.O., showed concentration-dependent biofilm inhibition, with a maximum of 91% at a concentration of 0.004% (v/v). The AlamarBlueTM assay also confirmed Linalool’s non-bactericidal anti-biofilm efficacy (0.004%). Linalool treatment impeded micro-colony formation, mature biofilm architecture, surface coverage, and biofilm thickness and impaired cell surface hydrophobicity and EPS production. Cysteine protease synthesis was quantified using the Azocasein assay, and Linalool treatment augmented its production. This suggests that Linalool destabilizes the biofilm matrix. It altered the expression of core regulons covRS, mga, srv, and ropB, and genes associated with virulence and biofilm formation, such as speB, dltA, slo, hasA, and ciaH, as revealed by qPCR analysis. Cytotoxicity analysis using human kidney cells (HEK) and the histopathological analysis in Danio rerio proved Linalool to be a druggable molecule against the biofilms formed by S. pyogenes. This is the first report on Linalool’s anti-biofilm and anti-virulence potential against S. pyogenes.

Lactiplantibacillus plantarum KAU007 Extract Modulates Critical Virulence Attributes and Biofilm Formation in Sinusitis Causing Streptococcus pyogenes

Streptococcus pyogenes is one of the most common bacteria causing sinusitis in children and adult patients. Probiotics are known to cause antagonistic effects on S. pyogenes growth and biofilm formation. In the present study, we demonstrated the anti-biofilm and anti-virulence properties of Lactiplantibacillus plantarum KAU007 against S. pyogenes ATCC 8668. The antibacterial potential of L. plantarum KAU007 metabolite extract (LME) purified from the cell-free supernatant of L. plantarum KAU007 was evaluated in terms of minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC). LME was further analyzed for its anti-biofilm potential using crystal violet assay and microscopic examination. Furthermore, the effect of LME was tested on the important virulence attributes of S. pyogenes, such as secreted protease production, hemolysis, extracellular polymeric substance production, and cell surface hydrophobicity. Additionally, the impact of LME on the expression of genes associated with biofilm formation and virulence attributes was analyzed using qPCR. The results revealed that LME significantly inhibited the growth and survival of S. pyogenes at a low concentration (MIC, 9.76 µg/mL; MBC, 39.06 µg/mL). Furthermore, LME inhibited biofilm formation and mitigated the production of extracellular polymeric substance at a concentration of 4.88 μg/mL in S. pyogenes. The results obtained from qPCR and biochemical assays advocated that LME suppresses the expression of various critical virulence-associated genes, which correspondingly affect various pathogenicity markers and were responsible for the impairment of virulence and biofilm formation in S. pyogenes. The non-hemolytic nature of LME and its anti-biofilm and anti-virulence properties against S. pyogenes invoke further investigation to study the role of LME as an antibacterial agent to combat streptococcal infections.

Hesperidin inhibits biofilm formation, virulence and staphyloxanthin synthesis in methicillin resistant Staphylococcus aureus by targeting SarA and CrtM: an in vitro and in silico approach

Methicillin resistant Staphylococcus aureus is considered multidrug resistant bacterium due to developing biofilm formation associated with antimicrobial resistance mechanisms. Therefore, inhibition of biofilm formation is an alternative therapeutic action to control MRSA infections. The present study revealed the non-antibacterial biofilm inhibitory potential of hesperidin against ATCC strain and clinical isolates of S. aureus. Hesperidin is a flavanone glycoside commonly found in citrus fruit. Hesperidin has been shown to exhibits numerous pharmacological activities. The present study aimed to evaluate the antibiofilm and antivirulence potential of hesperidin against MRSA. Results showed that hesperidin treatment significantly impedes lipase, hemolysin, autolysin, autoaggregation and staphyloxanthin production. Reductions of staphyloxanthin production possibly increase the MRSA susceptibility rate to H₂O₂ oxidative stress condition. In gene expression study revealed that hesperidin treatment downregulated the biofilm-associated gene (sarA), polysaccharide intracellular adhesion gene (icaA and icaD), autolysin (altA), fibronectin-binding protein (fnbA and fnbB) and staphyloxanthin production (crtM). Molecular docking analysis predicted the ability of hesperidin to interact with SarA and CrtM proteins involved in biofilm formation and staphyloxanthin production in MRSA.

Streptococcus pyogenes ("Group A Streptococcus"), a Highly Adapted Human Pathogen-Potential Implications of Its Virulence Regulation for Epidemiology and Disease Management

Streptococcus pyogenes (group A streptococci; GAS) is an exclusively human pathogen. It causes a variety of suppurative and non-suppurative diseases in people of all ages worldwide. Not all can be successfully treated with antibiotics. A licensed vaccine, in spite of its global importance, is not yet available. GAS express an arsenal of virulence factors responsible for pathological immune reactions. The transcription of all these virulence factors is under the control of three types of virulence-related regulators: (i) two-component systems (TCS), (ii) stand-alone regulators, and (iii) non-coding RNAs. This review summarizes major TCS and stand-alone transcriptional regulatory systems, which are directly associated with virulence control. It is suggested that this treasure of knowledge on the genetics of virulence regulation should be better harnessed for new therapies and prevention methods for GAS infections, thereby changing its global epidemiology for the better.

Pathogenic Mechanisms of Streptococcal Necrotizing Soft Tissue Infections

Necrotizing skin and soft tissue infections (NSTIs) are severe life-threatening and rapidly progressing infections. Beta-hemolytic streptococci, particularly S. pyogenes (group A streptococci (GAS)) but also S. dysgalactiae subsp. equisimilis (SDSE, most group G and C streptococcus), are the main causative agents of monomicrobial NSTIs and certain types, such as emm1 and emm3, are over-represented in NSTI cases. An arsenal of bacterial virulence factors contribute to disease pathogenesis, which is a complex and multifactorial process. In this chapter, we summarize data that have provided mechanistic and immuno-pathologic insight into host-pathogens interactions that contribute to tissue pathology in streptococcal NSTIs. The role of streptococcal surface associated and secreted factors contributing to the hyper-inflammatory state and immune evasion, bacterial load in the tissue and persistence strategies, including intracellular survival and biofilm formation, as well as strategies to mimic NSTIs in vitro are discussed.

A naturally occurring point mutation in the rocA gene of Streptococcus pyogenes confers the highly virulent phenotype

INTRODUCTION

Mucoid (MTB313) and nonmucoid (MTB314) strains of group A streptococcus (GAS) emm (antiphagocytic M protein) type 1 were simultaneously isolated from a single patient suffering from streptococcal meningitis. In a CD46-expressing transgenic (CD46 Tg) mouse model of subcutaneous infection into both hind footpads with MTB313 or MTB314, MTB313 showed considerably higher virulence than MTB314.

METHODS

The comparative genomic analysis based on the whole-genome sequencing revealed that MTB313 possessed an amber codon within rocA (sensory transduction protein kinase), but MTB314 did not carry this stop codon. Thereafter, MAT101 was generated from MTB313 by introducing pRocA, which contained the full-length rocA from MTB314, into the cloning plasmid pLZ12-Km2. MAT100 was also generated by introducing pLZ12-Km2 into MTB313.

RESULTS

Although MTB313 and MAT100 showed large quantities of cell-associated hyaluronic acid (HA) in the culture pellets, MTB314 and MAT101 showed small quantities of HA production. Finally, higher mortalities were observed in the MTB313- or MAT100-infected CD46 Tg mice than the MTB314- or MAT101-infected CD46 Tg mice.

CONCLUSIONS

These data indicate the possibility that a spontaneous point mutation in the rocA gene led to the highly virulent phenotype of M1 GAS.

5-Dodecanolide inhibits biofilm formation and virulence of Streptococcus pyogenes by suppressing core regulons of virulence

This study determined the antibiofilm and antivirulence potential of 5-Dodecanolide (DD) against an exclusive human pathogen Streptococcus pyogenes. Biofilm quantification assay showed antibiofilm efficacy of DD with maximum biofilm inhibition of 85% at 225 μg/mL concentration. Efficacy of antibacterial property of DD (225 μg/mL) was confirmed by CFU analysis and Alamar blue assay. Microscopic analyses evidently confirmed micro-colony formation, biofilm thickness and surface coverage were reduced upon DD treatment. In addition, based on the results of in vitro assays, it was noted that DD impaired the synthesis of surface hydrophobicity, slime, hyaluronic acid, hemolysin and protease production. Interestingly, DD increased the autoaggregation of S. pyogenes hence, facilitated enhanced recognition of clumped bacterial cells for innate immune clearance. The results were further validated by the reduced survival of DD treated S. pyogenes in healthy human blood. Consequently, based on the qPCR analysis DD altered the expression of core regulons srv, ropB, mga and genes associated with biofilm formation and virulence such as speB, dltA, srtB, sagA and slo. Hence, the overall results of the present study for the first time revealed the antibiofilm and antivirulence property of DD against clinically important pathogen S. pyogenes and further clinical investigations are required to assess the therapeutic use of DD.

Eucalyptol inhibits biofilm formation of Streptococcus pyogenes and its mediated virulence factors

Introduction. Streptococcus pyogenes is a diverse virulent synthesis pathogen responsible for invasive systemic infections. Establishment of antibiotic resistance in the pathogen has produced a need for new antibiofilm agents to control the biofilm formation and reduce biofilm-associated resistance development.Aim. The present study investigates the in vitro antibiofilm activity of eucalyptol against S. pyogenes.Methodology. The antibiofilm potential of eucalyptol was assessed using a microdilution method and their biofilm inhibition efficacy was visualized by microscopic analysis. The biochemical assays were performed to assess the influence of eucalyptol on virulence productions. Real-time PCR analysis was performed to evaluate the expression profile of the virulence genes.Results. Eucalyptol showed significant antibiofilm potential in a dose-dependent manner without affecting bacterial growth. Eucalyptol at 300 µg ml^-1 (biofilm inhibitory concentration) significantly inhibited the initial stage of biofilm formation in S. pyogenes. However, eucalyptol failed to diminish the mature biofilms of S. pyogenes at biofilm inhibitory concentration and it effectively reduced the biofilm formation on stainless steel, titanium, and silicone surfaces. The biochemical assay results revealed that eucalyptol greatly affects the cell-surface hydrophobicity, auto-aggregation, extracellular protease, haemolysis and hyaluronic acid synthesis. Further, the gene-expression analysis results showed significant downregulation of virulence gene expression upon eucalyptol treatment.Conclusion. The present study suggests that eucalyptol applies its antibiofilm assets by intruding the initial biofilm formation of S. pyogenes. Supplementary studies are needed to understand the mode of action involved in biofilm inhibition.

Quebrachitol inhibits biofilm formation and virulence production against methicillin-resistant Staphylococcus aureus

The present study evaluated the quebrachitol (QBC) antibiofilm and antivirulence potential against methicillin-resistant Staphylococcus aureus (MRSA). QBC inhibited MRSA biofilm formation at concentration dependent manner without affecting the bacterial growth. Then, QBC biofilm efficacy was confirmed with light and confocal laser scanning microscopy analysis. QBC treatment significantly inhibited the biofilm formation on stainless steel, titanium and silicone surfaces. Besides, QBC treatment significantly reduced the MRSA virulence productions such as lipase and hemolysis. Moreover, it reduced MRSA survival rate in the presence of hydrogen peroxide. QBC treatment inhibited the MRSA adherence on hydrophobic, hydrophilic, collagen coating and fibrinogen coating surfaces. As well as it significantly reduced the autolysin and bacterial aggregation progress. The real-time PCR analysis revealed the ability of QBC downregulated the virulence genes expression including global regulator sarA, agr and polysaccharide intracellular adhesion (PIA) encode ica. The cumulative results of the present study suggest that QBC as a potential agent to combat against MRSA pathogenesis.

Functional and Proteomic Analysis of Streptococcus pyogenes Virulence Upon Loss of Its Native Cas9 Nuclease

The public health impact of Streptococcus pyogenes (group A Streptococcus, GAS) as a top 10 cause of infection-related mortality in humans contrasts with its benefit to biotechnology as the main natural source of Cas9 nuclease, the key component of the revolutionary CRISPR-Cas9 gene editing platform. Despite widespread knowledge acquired in the last decade on the molecular mechanisms by which GAS Cas9 achieves precise DNA targeting, the functions of Cas9 in the biology and pathogenesis of its native organism remain unknown. In this study, we generated an isogenic serotype M1 GAS mutant deficient in Cas9 protein and compared its behavior and phenotypes to the wild-type parent strain. Absence of Cas9 was linked to reduced GAS epithelial cell adherence, reduced growth in human whole blood ex vivo, and attenuation of virulence in a murine necrotizing skin infection model. Virulence defects of the GAS Δcas9 strain were explored through quantitative proteomic analysis, revealing a significant reduction in the abundance of key GAS virulence determinants. Similarly, deletion of cas9 affected the expression of several known virulence regulatory proteins, indicating that Cas9 impacts the global architecture of GAS gene regulation.

Streptococcus pyogenes Causing Skin and Soft Tissue Infections Are Enriched in the Recently Emerged emm89 Clade 3 and Are Not Associated With Abrogation of CovRS

Although skin and soft tissue infections (SSTI) are the most common focal infections associated with invasive disease caused by Streptococcus pyogenes (Lancefield Group A streptococci - GAS), there is scarce information on the characteristics of isolates recovered from SSTI in temperate-climate regions. In this study, 320 GAS isolated from SSTI in Portugal were characterized by multiple typing methods and tested for antimicrobial susceptibility and SpeB activity. The covRS and ropB genes of isolates with no detectable SpeB activity were sequenced. The antimicrobial susceptibility profile was similar to that of previously characterized isolates from invasive infections (iGAS), presenting a decreasing trend in macrolide resistance. However, the clonal composition of SSTI between 2005 and 2009 was significantly different from that of contemporary iGAS. Overall, iGAS were associated with emm1 and emm3, while SSTI were associated with emm89, the dominant emm type among SSTI (19%). Within emm89, SSTI were only significantly associated with isolates lacking the hasABC locus, suggesting that the recently emerged emm89 clade 3 may have an increased potential to cause SSTI. Reflecting these associations between emm type and disease presentation, there were also differences in the distribution of emm clusters, sequence types, and superantigen gene profiles between SSTI and iGAS. According to the predicted ability of each emm cluster to interact with host proteins, iGAS were associated with the ability to bind fibrinogen and albumin, whereas SSTI isolates were associated with the ability to bind C4BP, IgA, and IgG. SpeB activity was absent in 79 isolates (25%), in line with the proportion previously observed among iGAS. Null covS and ropB alleles (predicted to eliminate protein function) were detected in 10 (3%) and 12 (4%) isolates, corresponding to an underrepresentation of mutations impairing CovRS function in SSTI relative to iGAS. Overall, these results indicate that the isolates responsible for SSTI are genetically distinct from those recovered from normally sterile sites, supporting a role for mutations impairing CovRS activity specifically in invasive infection and suggesting that this role relies on a differential regulation of other virulence factors besides SpeB.

Fukugiside, a biflavonoid from Garcinia travancorica inhibits biofilm formation of Streptococcus pyogenes and its associated virulence factors

PURPOSE

Streptococcus pyogenes, a notorious human pathogen thatis responsible for various invasive and non-invasive diseases, possesses multiple virulence armaments, including biofilm formation. The current study demonstrates the anti-biofilm and anti-virulence potential of fukugiside, a biflavonoid isolated from Garciniatravancorica, against S. pyogenes.

METHODOLOGY

The anti-biofilm activity of fukugiside was assessed and established using microdilution and microscopic analysis. Biochemical assays were performed to assess the effects of fukugiside on important virulence factors, which were further validated using quantitative real-time PCR and in vivo analysis in Caenorhabditis elegans.

RESULTS

Fukugiside exhibited concentration-dependent biofilm inhibition (79 to 96 %) against multiple M serotypes of S. pyogenes (M1, M56, M65, M74, M100 and st38) with a minimum biofilm inhibitory concentration of 80 µg ml^-1. Electron microscopy and biochemical assay revealed a significant reduction in extracellular polymeric substance production. The results for the microbial adhesion to hydrocarbon assay, extracellular protease quantification and differential regulation of the dltA, speB, srv and ropB genes suggested that fukugiside probably inhibits biofilm formation by lowering cell surface hydrophobicity and destabilizing the biofilm matrix. The enhanced susceptibility to phagocytosis evidenced in the blood survival assay goes in unison with the downregulation of mga. The downregulation of important virulence factor-encoding genes such as hasA, slo and col370 suggested impaired virulence. In vivo analysis in C. elegans evinced the non-toxic nature of fukugiside and its anti-virulence potential against S. pyogenes.

CONCLUSION

Fukugiside exhibits potent anti-biofilm and anti-virulence activity against different M serotypes of S. pyogenes. It is also non-toxic, which augurs well for its clinical application.

Streptococcal Cysteine Protease-Mediated Cleavage of Desmogleins Is Involved in the Pathogenesis of Cutaneous Infection

Streptococcus pyogenes is responsible for a wide variety of cutaneous infections ranging from superficial impetigo to fulminant invasive necrotizing fasciitis. Dysfunction of desmosomes is associated with the pathogenesis of cutaneous diseases. We identified streptococcal pyrogenic exotoxin B (SpeB) as a proteolytic factor that cleaves the extracellular domains of desmoglein 1 and 3. In an epicutaneous infection model, lesional skin infected with an speB deletion mutant were significantly smaller as compared to those caused by the wild-type strain. Furthermore, immunohistological analysis indicated cleavage of desmogleins that developed around the invasion site of the wild-type strain. In contrast, the speB mutant was preferentially found on the epidermis surface layer. Taken together, our findings provide evidence that SpeB-mediated degradation of desmosomes has a pathogenic role in development of S. pyogenes cutaneous infection.

Genetic and Structural Analyses of RRNPP Intercellular Peptide Signaling of Gram-Positive Bacteria

Bacteria use diffusible chemical messengers, termed pheromones, to coordinate gene expression and behavior among cells in a community by a process known as quorum sensing. Pheromones of many gram-positive bacteria, such as Bacillus and Streptococcus, are small, linear peptides secreted from cells and subsequently detected by sensory receptors such as those belonging to the large family of RRNPP proteins. These proteins are cytoplasmic pheromone receptors sharing a structurally similar pheromone-binding domain that functions allosterically to regulate receptor activity. X-ray crystal structures of prototypical RRNPP members have provided atomic-level insights into their mechanism and regulation by pheromones. This review provides an overview of RRNPP prototype signaling; describes the structure-function of this protein family, which is spread widely among gram-positive bacteria; and suggests approaches to target RRNPP systems in order to manipulate beneficial and harmful bacterial behaviors.

Streptococcal Immunity Is Constrained by Lack of Immunological Memory following a Single Episode of Pyoderma

The immunobiology underlying the slow acquisition of skin immunity to group A streptococci (GAS), is not understood, but attributed to specific virulence factors impeding innate immunity and significant antigenic diversity of the type-specific M-protein, hindering acquired immunity. We used a number of epidemiologically distinct GAS strains to model the development of acquired immunity. We show that infection leads to antibody responses to the serotype-specific determinants on the M-protein and profound protective immunity; however, memory B cells do not develop and immunity is rapidly lost. Furthermore, antibodies do not develop to a conserved M-protein epitope that is able to induce immunity following vaccination. However, if re-infected with the same strain within three weeks, enduring immunity and memory B-cells (MBCs) to type-specific epitopes do develop. Such MBCs can adoptively transfer protection to naïve recipients. Thus, highly protective M-protein-specific MBCs may never develop following a single episode of pyoderma, contributing to the slow acquisition of immunity and to streptococcal endemicity in at-risk populations.

GAS skin infections pose a significant health problem in the tropics. They are highly prevalent in developing countries as well as amongst the Indigenous populations of developed countries. In at-risk impoverished communities the epidemiology of GAS infections is very dynamic, leading to very high rates of streptococcal-associated serious pathology including rheumatic heart disease, glomerulonephritis and invasive GAS disease. Immunity to GAS takes over 20 years to develop and this has been attributed to sequence diversity of the type-specific surface M-protein. There are more than 250 different strains of GAS and it known that antibodies to the amino-terminal segment of the M-protein can kill organisms in a strain-specific manner in vitro. In the present study, using four different strains of GAS isolated from the skin lesions of Aboriginal patients in the Northern Territory of Australia, we make the discovery that skin infection does not induce long-lived type-specific immunity. However, following reinfection with the same strain memory B cells are generated and long-term strain-protective immunity then develops. The dependence on reinfection for the development of strain-specific immunity compounds with antigenic diversity of the M-protein and provides a rational explanation for the very slow acquisition of streptococcal immunity.

PptAB Exports Rgg Quorum-Sensing Peptides in Streptococcus

A transposon mutagenesis screen designed to identify mutants that were defective in peptide-pheromone signaling of the Rgg2/Rgg3 pathway in Streptococcus pyogenes generated insertions in sixteen loci displaying diminished reporter activity. Fourteen unique transposon insertions were mapped to pptAB, an ABC-type transporter recently described to export sex pheromones of Enterococcus faecalis. Consistent with an idea that PptAB exports signaling peptides, the pheromones known as SHPs (short hydrophobic peptides) were no longer detected in cell-free culture supernatants in a generated deletion mutant of pptAB. PptAB exporters are conserved among the Firmicutes, but their function and substrates remain unclear. Therefore, we tested a pptAB mutant generated in Streptococcus mutans and found that while secretion of heterologously expressed SHP peptides required PptAB, secretion of the S. mutans endogenous pheromone XIP (sigX inducing peptide) was only partially disrupted, indicating that a secondary secretion pathway for XIP exists.

Streptococcal toxins: role in pathogenesis and disease

Group A Streptococcus (Streptococcus pyogenes), group B Streptococcus (Streptococcus agalactiae) and Streptococcus pneumoniae (pneumococcus) are host-adapted bacterial pathogens among the leading infectious causes of human morbidity and mortality. These microbes and related members of the genus Streptococcus produce an array of toxins that act against human cells or tissues, resulting in impaired immune responses and subversion of host physiological processes to benefit the invading microorganism. This toxin repertoire includes haemolysins, proteases, superantigens and other agents that ultimately enhance colonization and survival within the host and promote dissemination of the pathogen.

The majority of 9,729 group A streptococcus strains causing disease secrete SpeB cysteine protease: pathogenesis implications

Group A streptococcus (GAS), the causative agent of pharyngitis and necrotizing fasciitis, secretes the potent cysteine protease SpeB. Several lines of evidence suggest that SpeB is an important virulence factor. SpeB is expressed in human infections, protects mice from lethal challenge when used as a vaccine, and contributes significantly to tissue destruction and dissemination in animal models. However, recent descriptions of mutations in genes implicated in SpeB production have led to the idea that GAS may be under selective pressure to decrease secreted SpeB protease activity during infection. Thus, two divergent hypotheses have been proposed. One postulates that SpeB is a key contributor to pathogenesis; the other, that GAS is under selection to decrease SpeB during infection. In order to distinguish between these alternative hypotheses, we performed casein hydrolysis assays to measure the SpeB protease activity secreted by 6,775 GAS strains recovered from infected humans. The results demonstrated that 84.3% of the strains have a wild-type SpeB protease phenotype. The availability of whole-genome sequence data allowed us to determine the relative frequencies of mutations in genes implicated in SpeB production. The most abundantly mutated genes were direct transcription regulators. We also sequenced the genomes of 2,954 GAS isolates recovered from nonhuman primates with experimental necrotizing fasciitis. No mutations that would result in a SpeB-deficient phenotype were identified. Taken together, these data unambiguously demonstrate that the great majority of GAS strains recovered from infected humans secrete wild-type levels of SpeB protease activity. Our data confirm the important role of SpeB in GAS pathogenesis and help end a long-standing controversy.

Induction of a quorum sensing pathway by environmental signals enhances group A streptococcal resistance to lysozyme

The human-restricted pathogen Streptococcus pyogenes (Group A Streptococcus, GAS) is responsible for wide-ranging pathologies at numerous sites in the body but has the proclivity to proliferate in individuals asymptomatically. The ability to survive in diverse tissues is undoubtedly benefited by sensory pathways that recognize environmental cues corresponding to stress and nutrient availability and thereby trigger adaptive responses. We investigated the impact that environmental signals contribute to cell-to-cell chemical communication [quorum sensing (QS)] by monitoring activity of the Rgg2/Rgg3 and SHP-pheromone system in GAS. We identified metal limitation and the alternate carbon source mannose as two environmental indicators likely to be encountered by GAS in the host that significantly induced the Rgg-SHP system. Disruption of the metal regulator MtsR partially accounted for the response to metal depletion, whereas ptsABCD was primarily responsible for QS induction due to mannose, but each sensory system induced Rgg-SHP signaling apparently by different mechanisms. Significantly, we found that induction of QS, regardless of the GAS serotype tested, led to enhanced resistance to the antimicrobial agent lysozyme. These results indicate the benefits for GAS to integrate environmental signals with intercellular communication pathways in protection from host defenses.

Consequences of the variability of the CovRS and RopB regulators among Streptococcus pyogenes causing human infections

To evaluate the importance of covRS and ropB mutations in invasive disease caused by Group A Streptococci (GAS), we determined the sequence of the covRS and ropB genes of 191 isolates from invasive infections and pharyngitis, comprising a diverse set of emm types and multilocus sequence types. The production of SpeB and the activity of NAD glycohydrolase (NADase) and streptolysin S (SLS) were evaluated. The results support the acquisition of null covS alleles (predicted to eliminate protein function), resulting in downregulation of SpeB and upregulation of NADase and SLS, as a mechanism possibly contributing to higher invasiveness. Among the isolates tested, this mechanism was found to be uncommon (10% of invasive isolates) and was not more prevalent among clones with enhanced invasiveness (including M1T1) but occurred in diverse genetic backgrounds. In lineages such as emm64, these changes did not result in upregulation of NADase and SLS, highlighting the diversity of regulatory pathways in GAS. Despite abrogating SpeB production, null alleles in ropB were not associated with invasive infection. The covRS and ropB genes are under stabilising selection and no expansion of isolates carrying null alleles has been observed, suggesting that the presence of these regulators is important for overall fitness.

Streptococcus pyogenes biofilms-formation, biology, and clinical relevance

Streptococcus pyogenes (group A streptococci, GAS) is an exclusive human bacterial pathogen. The virulence potential of this species is tremendous. Interactions with humans range from asymptomatic carriage over mild and superficial infections of skin and mucosal membranes up to systemic purulent toxic-invasive disease manifestations. Particularly the latter are a severe threat for predisposed patients and lead to significant death tolls worldwide. This places GAS among the most important Gram-positive bacterial pathogens. Many recent reviews have highlighted the GAS repertoire of virulence factors, regulators and regulatory circuits/networks that enable GAS to colonize the host and to deal with all levels of the host immune defense. This covers in vitro and in vivo studies, including animal infection studies based on mice and more relevant, macaque monkeys. It is now appreciated that GAS, like many other bacterial species, do not necessarily exclusively live in a planktonic lifestyle. GAS is capable of microcolony and biofilm formation on host cells and tissues. We are now beginning to understand that this feature significantly contributes to GAS pathogenesis. In this review we will discuss the current knowledge on GAS biofilm formation, the biofilm-phenotype associated virulence factors, regulatory aspects of biofilm formation, the clinical relevance, and finally contemporary treatment regimens and future treatment options.

A naturally occurring single amino acid replacement in multiple gene regulator of group A Streptococcus significantly increases virulence

Single-nucleotide polymorphisms (SNPs) are the most common source of genetic variation within a species; however, few investigations demonstrate how naturally occurring SNPs may increase strain virulence. We recently used group A Streptococcus as a model pathogen to study bacteria strain genotype-patient disease phenotype relationships. Whole-genome sequencing of approximately 800 serotype M59 group A Streptococcus strains, recovered during an outbreak of severe invasive infections across North America, identified a disproportionate number of SNPs in the gene encoding multiple gene regulator of group A Streptococcus (mga). Herein, we report results of studies designed to test the hypothesis that the most commonly occurring SNP, encoding a replacement of arginine for histidine at codon 201 of Mga (H201R), significantly increases virulence. Whole transcriptome analysis revealed that the H201R replacement significantly increased expression of mga and 54 other genes, including many proven virulence factors. Compared to the wild-type strain, a H201R isogenic mutant strain caused significantly larger skin lesions in mice. Serial quantitative bacterial culture and noninvasive magnetic resonance imaging also demonstrated that the isogenic H201R strain was significantly more virulent in a nonhuman primate model of joint infection. These findings show that the H201R replacement in Mga increases the virulence of M59 group A Streptococcus and provide new insight to how a naturally occurring SNP in bacteria contributes to human disease phenotypes.

Mutual exclusivity of hyaluronan and hyaluronidase in invasive group A Streptococcus

A recent analysis of group A Streptococcus (GAS) invasive infections in Australia has shown a predominance of M4 GAS, a serotype recently reported to lack the antiphagocytic hyaluronic acid (HA) capsule. Here, we use molecular genetics and bioinformatics techniques to characterize 17 clinical M4 isolates associated with invasive disease in children during this recent epidemiology. All M4 isolates lacked HA capsule, and whole genome sequence analysis of two isolates revealed the complete absence of the hasABC capsule biosynthesis operon. Conversely, M4 isolates possess a functional HA-degrading hyaluronate lyase (HylA) enzyme that is rendered nonfunctional in other GAS through a point mutation. Transformation with a plasmid expressing hasABC restored partial encapsulation in wild-type (WT) M4 GAS, and full encapsulation in an isogenic M4 mutant lacking HylA. However, partial encapsulation reduced binding to human complement regulatory protein C4BP, did not enhance survival in whole human blood, and did not increase virulence of WT M4 GAS in a mouse model of systemic infection. Bioinformatics analysis found no hasABC homologs in closely related species, suggesting that this operon was a recent acquisition. These data showcase a mutually exclusive interaction of HA capsule and active HylA among strains of this leading human pathogen.

Quorum sensing in group A Streptococcus

Quorum sensing (QS) is a widespread phenomenon in the microbial world that has important implications in the coordination of population-wide responses in several bacterial pathogens. In Group A Streptococcus (GAS), many questions surrounding QS systems remain to be solved pertaining to their function and their contribution to the GAS lifestyle in the host. The QS systems of GAS described to date can be categorized into four groups: regulator gene of glucosyltransferase (Rgg), Sil, lantibiotic systems, and LuxS/AI-2. The Rgg family of proteins, a conserved group of transcription factors that modify their activity in response to signaling peptides, has been shown to regulate genes involved in virulence, biofilm formation and competence. The sil locus, whose expression is regulated by the activity of signaling peptides and a putative two-component system (TCS), has been implicated on regulating genes involved with invasive disease in GAS isolates. Lantibiotic regulatory systems are involved in the production of bacteriocins and their autoregulation, and some of these genes have been shown to target both bacterial organisms as well as processes of survival inside the infected host. Finally AI-2 (dihydroxy pentanedione, DPD), synthesized by the LuxS enzyme in several bacteria including GAS, has been proposed to be a universal bacterial communication molecule. In this review we discuss the mechanisms of these four systems, the putative functions of their targets, and pose critical questions for future studies.

In silico and in vitro studies of cinnamaldehyde and their derivatives against LuxS in Streptococcus pyogenes: effects on biofilm and virulence genes

The LuxS-based signalling pathway has an important role in physiological and pathogenic functions that are capable of causing different infections. In the present study, cinnamaldehyde (CN) and their derivatives were evaluated for their inhibitory efficiency against LuxS by molecular modelling, docking, dynamics and free-energy calculations. Sequence and structure-similarity analysis of LuxS protein, five different amino acids were found to be highly conserved, of which GLY128 was identified as the key residue involved in the effective binding of the ligands. Quantum-polarized ligand docking protocol showed that 2nitro and 4nitro CN has a higher binding efficiency than CN, which very well corroborates with the in vitro studies. COMSTAT analysis for the microscopic images of the S. pyogenes biofilm showed that the ligands have antibiofilm potential. In addition, the results of quantitative polymerase chain reaction (qPCR) analysis revealed that the transcripts treated with the compounds showed decrease in luxS expression, which directly reflects with the reduction in expression of speB. No substantial effect was observed on the virulence regulator (srv) transcript. These results confirm that speB is controlled by the regulation of luxS. The decreased rate of S. pyogenes survival in the presence of these ligands envisaged the fact that the compounds could readily enhance opsonophagocytosis with the reduction of virulence factor secretion. Thus, the overall data supports the use of CN derivatives against quorum sensing-mediated infections caused by S. pyogenes.

Mutations in the control of virulence sensor gene from Streptococcus pyogenes after infection in mice lead to clonal bacterial variants with altered gene regulatory activity and virulence

The cluster of virulence sensor (CovS)/responder (CovR) two-component operon (CovRS) regulates ∼15% of the genes of the Group A Streptococcal pyogenes (GAS) genome. Bacterial clones containing inactivating mutations in the covS gene have been isolated from patients with virulent invasive diseases. We report herein an assessment of the nature and types of covS mutations that can occur in both virulent and nonvirulent GAS strains, and assess whether a nonvirulent GAS can attain enhanced virulence through this mechanism. A group of mice were infected with a globally-disseminated clonal M1T1 GAS (isolate 5448), containing wild-type (WT) CovRS (5448/CovR⁺S⁺), or less virulent engineered GAS strains, AP53/CovR⁺S⁺ and Manfredo M5/CovR⁺S⁺. SpeB negative GAS clones from wound sites and/or from bacteria disseminated to the spleen were isolated and the covS gene was subjected to DNA sequence analysis. Numerous examples of inactivating mutations were found in CovS in all regions of the gene. The mutations found included frame-shift insertions and deletions, and in-frame small and large deletions in the gene. Many of the mutations found resulted in early translation termination of CovS. Thus, the covS gene is a genomic mutagenic target that gives GAS enhanced virulence. In cases wherein CovS⁻ was discovered, these clonal variants exhibited high lethality, further suggesting that randomly mutated covS genes occur during the course of infection, and lead to the development of a more invasive infection.

Defining a pro-inflammatory neutrophil phenotype in response to schistosome eggs

Neutrophils contribute to the pathological processes of a number of inflammatory disorders, including rheumatoid arthritis, sepsis and cystic fibrosis. Neutrophils also play prominent roles in schistosomiasis japonica liver fibrosis, being central mediators of inflammation following granuloma formation. In this study, we investigated the interaction between Schistosoma japonicum eggs and neutrophils, and the effect of eggs on the inflammatory phenotype of neutrophils. Our results showed significant upregulated expression of pro-inflammatory cytokines (IL-1α, IL-1β and IL-8) and chemokines (CCL3, CCL4 and CXCL2) in neutrophils after 4 h in vitro stimulation with S. japonicum eggs. Furthermore, mitochondrial DNA was released by stimulated neutrophils, and induced the production of matrix metalloproteinase 9 (MMP-9), a protease involved in inflammation and associated tissue destruction. We also found that intact live eggs and isolated soluble egg antigen (SEA) triggered the release of neutrophil extracellular traps (NETs), but, unlike those reported in bacterial or fungal infection, NETs did not kill schistosome eggs in vitro. Together these show that S. japonicum eggs can induce the inflammatory phenotype of neutrophils, and further our understanding of the host-parasite interplay that takes place within the in vivo microenvironment of schistosome-induced granuloma. These findings represent novel findings in a metazoan parasite, and confirm characteristics of NETs that have until now, only been observed in response to protozoan pathogens.

Disease manifestations and pathogenic mechanisms of Group A Streptococcus

Streptococcus pyogenes, also known as group A Streptococcus (GAS), causes mild human infections such as pharyngitis and impetigo and serious infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. Furthermore, repeated GAS infections may trigger autoimmune diseases, including acute poststreptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease. Combined, these diseases account for over half a million deaths per year globally. Genomic and molecular analyses have now characterized a large number of GAS virulence determinants, many of which exhibit overlap and redundancy in the processes of adhesion and colonization, innate immune resistance, and the capacity to facilitate tissue barrier degradation and spread within the human host. This improved understanding of the contribution of individual virulence determinants to the disease process has led to the formulation of models of GAS disease progression, which may lead to better treatment and intervention strategies. While GAS remains sensitive to all penicillins and cephalosporins, rising resistance to other antibiotics used in disease treatment is an increasing worldwide concern. Several GAS vaccine formulations that elicit protective immunity in animal models have shown promise in nonhuman primate and early-stage human trials. The development of a safe and efficacious commercial human vaccine for the prophylaxis of GAS disease remains a high priority.

Disease manifestations and pathogenic mechanisms of Group A Streptococcus

Streptococcus pyogenes, also known as group A Streptococcus (GAS), causes mild human infections such as pharyngitis and impetigo and serious infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. Furthermore, repeated GAS infections may trigger autoimmune diseases, including acute poststreptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease. Combined, these diseases account for over half a million deaths per year globally. Genomic and molecular analyses have now characterized a large number of GAS virulence determinants, many of which exhibit overlap and redundancy in the processes of adhesion and colonization, innate immune resistance, and the capacity to facilitate tissue barrier degradation and spread within the human host. This improved understanding of the contribution of individual virulence determinants to the disease process has led to the formulation of models of GAS disease progression, which may lead to better treatment and intervention strategies. While GAS remains sensitive to all penicillins and cephalosporins, rising resistance to other antibiotics used in disease treatment is an increasing worldwide concern. Several GAS vaccine formulations that elicit protective immunity in animal models have shown promise in nonhuman primate and early-stage human trials. The development of a safe and efficacious commercial human vaccine for the prophylaxis of GAS disease remains a high priority.

RocA truncation underpins hyper-encapsulation, carriage longevity and transmissibility of serotype M18 group A streptococci

Group A streptococcal isolates of serotype M18 are historically associated with epidemic waves of pharyngitis and the non-suppurative immune sequela rheumatic fever. The serotype is defined by a unique, highly encapsulated phenotype, yet the molecular basis for this unusual colony morphology is unknown. Here we identify a truncation in the regulatory protein RocA, unique to and conserved within our serotype M18 GAS collection, and demonstrate that it underlies the characteristic M18 capsule phenotype. Reciprocal allelic exchange mutagenesis of rocA between M18 GAS and M89 GAS demonstrated that truncation of RocA was both necessary and sufficient for hyper-encapsulation via up-regulation of both precursors required for hyaluronic acid synthesis. Although RocA was shown to positively enhance covR transcription, quantitative proteomics revealed RocA to be a metabolic regulator with activity beyond the CovR/S regulon. M18 GAS demonstrated a uniquely protuberant chain formation following culture on agar that was dependent on excess capsule and the RocA mutation. Correction of the M18 rocA mutation reduced GAS survival in human blood, and in vivo naso-pharyngeal carriage longevity in a murine model, with an associated drop in bacterial airborne transmission during infection. In summary, a naturally occurring truncation in a regulator explains the encapsulation phenotype, carriage longevity and transmissibility of M18 GAS, highlighting the close interrelation of metabolism, capsule and virulence.

Group A streptococcus is an important human pathogen which produces a polysaccharide capsule that confers resistance to killing by white blood cells and allows bacterial adherence to host epithelial surfaces. Serotype M18 isolates over-produce capsule, creating a unique and characteristic appearance when grown on blood agar. This feature may underlie the waves of infectious pharyngitis and subsequent onset of rheumatic fever associated with this serotype. The reason for hyper-encapsulation of M18 GAS is unknown. Here we show that a naturally-occurring truncation in an important regulatory protein, RocA, underlies serotype M18 hyper-encapsulation. By correcting the truncation we were able to reverse hyper-encapsulation, modify the 3-D structural morphology of bacteria within colonies and alter the overall protein expression pattern of the bacterium. We were able to reproduce characteristics of M18 streptococci in a different serotype strain by introducing the same truncation mutation. It was also possible to show that the truncation in RocA led to prolonged nasopharyngeal carriage of GAS in mice and also promoted bacterial airborne transmission. Thus, the propensity for M18 isolates to be associated with outbreaks of pharyngitis and rheumatic fever may be accounted for by the level of encapsulation induced by truncation of the regulatory protein RocA.

Enterococcal Rgg-like regulator ElrR activates expression of the elrA operon

The Enterococcus faecalis leucine-rich protein ElrA promotes virulence by stimulating bacterial persistence in macrophages and production of the interleukin-6 (IL-6) cytokine. The ElrA protein is encoded within an operon that is poorly expressed under laboratory conditions but induced in vivo. In this study, we identify ef2687 (renamed elrR), which encodes a member of the Rgg (regulator gene for glucosyltransferase) family of putative regulatory proteins. Using quantitative reverse transcription-PCR, translational lacZ fusions, and electrophoretic mobility shift assays, we demonstrate that ElrR positively regulates expression of elrA. These results correlate with the attenuated virulence of the ΔelrR strain in a mouse peritonitis model. Virulence of simple and double elrR and elrA deletion mutants also suggests a remaining ElrR-independent expression of elrA in vivo and additional virulence-related genes controlled by ElrR.

Streptococcal collagen-like protein A and general stress protein 24 are immunomodulating virulence factors of group A Streptococcus

In Western countries, invasive infections caused by M1T1 serotype group A Streptococcus (GAS) are epidemiologically linked to mutations in the control of virulence regulatory 2-component operon (covRS). In indigenous communities and developing countries, severe GAS disease is associated with genetically diverse non-M1T1 GAS serotypes. Hypervirulent M1T1 covRS mutant strains arise through selection by human polymorphonuclear cells for increased expression of GAS virulence factors such as the DNase Sda1, which promotes neutrophil resistance. The GAS bacteremia isolate NS88.2 (emm 98.1) is a covS mutant that exhibits a hypervirulent phenotype and neutrophil resistance yet lacks the phage-encoded Sda1. Here, we have employed a comprehensive systems biology (genomic, transcriptomic, and proteomic) approach to identify NS88.2 virulence determinants that enhance neutrophil resistance in the non-M1T1 GAS genetic background. Using this approach, we have identified streptococcal collagen-like protein A and general stress protein 24 proteins as NS88.2 determinants that contribute to survival in whole blood and neutrophil resistance in non-M1T1 GAS. This study has revealed new factors that contribute to GAS pathogenicity that may play important roles in resisting innate immune defenses and the development of human invasive infections.

A bacterial pathogen co-opts host plasmin to resist killing by cathelicidin antimicrobial peptides

The bacterial pathogen Group A Streptococcus (GAS) colonizes epithelial and mucosal surfaces and can cause a broad spectrum of human disease. Through the secreted plasminogen activator streptokinase (Ska), GAS activates human plasminogen into plasmin and binds it to the bacterial surface. The resulting surface plasmin protease activity has been proposed to play a role in disrupting tissue barriers, promoting invasive spread of the bacterium. We investigated whether this surface protease activity could aid the immune evasion role through degradation of the key innate antimicrobial peptide LL-37, the human cathelicidin. Cleavage products of plasmin-degraded LL-37 were analyzed by matrix-assisted laser desorption ionization mass spectrometry. Ska-deficient GAS strains were generated by targeted allelic exchange mutagenesis and confirmed to lack surface plasmin activity after growth in human plasma or media supplemented with plasminogen and fibrinogen. Loss of surface plasmin activity left GAS unable to efficiently degrade LL-37 and increased bacterial susceptibility to killing by the antimicrobial peptide. When mice infected with GAS were simultaneously treated with the plasmin inhibitor aprotinin, a significant reduction in the size of necrotic skin lesions was observed. Together these data reveal a novel immune evasion strategy of the human pathogen: co-opting the activity of a host protease to evade peptide-based innate host defenses.

Superantigen gene complement of Streptococcus pyogenes--relationship with other typing methods and short-term stability

The profiling of the superantigen (SAg) encoding genes has been frequently used as a complementary typing method for group A streptococci (GAS), but a confusing gene nomenclature and a large diversity of primers used in screening has led to some conflicting results. The aim of this work was to develop a polymerase chain reaction (PCR) method capable of efficiently amplifying all the known allelic variants of these genes, and to evaluate the congruence of this methodology with other commonly used molecular typing methods. The presence of the 11 known SAg genes and two other exotoxin-encoding genes (speB and speF) was tested in a collection of 480 clinical GAS isolates, using two multiplex PCR reactions. The SAg gene profile was compared with other typing methods. Four naturally occurring deletions involving the genes speB, speF, and rgg were characterized, two of which were found among invasive isolates. The absence of the chromosomally encoded genes speG and smeZ was supported by Southern blot hybridization and associated with specific GAS lineages, while the presence of phage-encoded genes was more variable. Positive associations between SAg genes or between SAg profiles and emm types or pulsed-field gel electrophoresis (PFGE) clusters were observed. The results suggest that the SAg profile diversifies faster than other properties commonly used for molecular typing, such as emm type and multilocus sequence typing (MLST) sequence types (STs), and can be a useful complement in GAS molecular epidemiology. Still, the short-term stability of the SAg gene profile among prevalent genetic lineages may largely explain the observed associations between SAg genes.

Tracing the evolutionary history of the pandemic group A streptococcal M1T1 clone

The past 50 years has witnessed the emergence of new viral and bacterial pathogens with global effect on human health. The hyperinvasive group A Streptococcus (GAS) M1T1 clone, first detected in the mid-1980s in the United States, has since disseminated worldwide and remains a major cause of severe invasive human infections. Although much is understood regarding the capacity of this pathogen to cause disease, much less is known of the precise evolutionary events selecting for its emergence. We used high-throughput technologies to sequence a World Health Organization strain collection of serotype M1 GAS and reconstructed its phylogeny based on the analysis of core genome single-nucleotide polymorphisms. We demonstrate that acquisition of a 36-kb genome segment from serotype M12 GAS and the bacteriophage-encoded DNase Sda1 led to increased virulence of the M1T1 precursor and occurred relatively early in the molecular evolutionary history of this strain. The more recent acquisition of the phage-encoded superantigen SpeA is likely to have provided selection advantage for the global dissemination of the M1T1 clone. This study provides an exemplar for the evolution and emergence of virulent clones from microbial populations existing commensally or causing only superficial infection.

Synergistic effects of streptolysin S and streptococcal pyrogenic exotoxin B on the mouse model of group A streptococcal infection

Streptococcus pyogenes is a group A streptococcus (GAS) and an important human pathogen that causes a variety of diseases. Streptococcal pyrogenic exotoxin B (SPE B) and streptolysin S (SLS) are important virulence factors involved in GAS infection, but it is not clear which one is more virulent. Using an air pouch infection model, the wild-type strain NZ131, its isogenic mutants, and complementary mutants were used to examine the effects of SPE B and SLS on GAS infection. The results of the skin lesion and mouse mortality assays showed that although SPE B and SLS had a synergistic effect on GAS infection, SPE B played a more important role in local tissue damage while SLS had a more prominent effect on mouse mortality. Surveys of the exudates from the air pouch revealed that the expression of inflammatory cytokines was significantly inhibited in the sagB/speB-double-mutant JM4-infected mice. Furthermore, in vivo and in vitro studies showed that the isogenic mutant strains were more susceptible to the immune cell killing than the wild-type strain and that the sagB/speB-double-mutant JM4 was the most sensitive among these strains. Moreover, infection with the sagB/speB-double-mutant JM4 strain caused the least amount of macrophage apoptosis compared to infection with the wild-type NZ131 and the other complementary strains, which express only SPE B or SLS or both. Taken together, these results indicate that both SPE B and SLS contributed to GAS evasion from immune cell killing, local tissue damage, and mouse mortality.

Polymorphisms in regulator of protease B (RopB) alter disease phenotype and strain virulence of serotype M3 group A Streptococcus

Whole-genome sequencing of serotype M3 group A streptococci (GAS) from oropharyngeal and invasive infections in Ontario recently showed that the gene encoding regulator of protease B (RopB) is highly polymorphic in this population. To test the hypothesis that ropB is under diversifying selective pressure among all serotype M3 GAS strains, we sequenced this gene in 1178 strains collected from different infection types, geographic regions, and time periods. The results confirmed our hypothesis and discovered a significant association between mutant ropB alleles, decreased activity of its major regulatory target SpeB, and pharyngitis. Additionally, isoallelic strains with ropB polymorphisms were significantly less virulent in a mouse model of necrotizing fasciitis. These studies provide a model strategy for applying whole-genome sequencing followed by deep single-gene sequencing to generate new insight to the rapid evolution and virulence regulation of human pathogens.

Molecular insight into invasive group A streptococcal disease

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.

Role of serine/threonine phosphatase (SP-STP) in Streptococcus pyogenes physiology and virulence

Reversible phosphorylation is the key mechanism regulating several cellular events in prokaryotes and eukaryotes. In prokaryotes, signal transduction is perceived to occur primarily via the two-component signaling system involving histidine kinases and cognate response regulators. Although an alternative regulatory pathway controlled by the eukaryote-type serine/threonine kinase (Streptococcus pyogenes serine/threonine kinase; SP-STK) has been shown to modulate bacterial growth, division, adherence, invasion, and virulence in group A Streptococcus (GAS; S. pyogenes), the precise role of the co-transcribing serine/threonine phosphatase (SP-STP) has remained enigmatic. In this context, this is the first report describing the construction and characterization of non-polar SP-STP mutants in two different strains of Type M1 GAS. The STP knock-out mutants displayed increased bacterial chain lengths in conjunction with thickened cell walls, significantly reduced capsule and hemolysin production, and restoration of the phenotypes postcomplementation. The present study also reveals important contribution of cognately regulated-reversible phosphorylation by SP-STK/SP-STP on two major response regulators of two-component systems, WalRK and CovRS. We also demonstrate a distinct role of SP-STP in terms of expression of surface proteins and SpeB in a strain-specific manner. Further, the attenuation of virulence in the absence of STP and its restoration only in the complemented strains that were generated by the use of a low copy plasmid and not by a high copy one emphasize not only the essential role of STP in virulence but also highlight the tightly regulated SP-STP/SP-STK-mediated cognate functions. SP-STP thus is an important regulator of GAS virulence and plays a critical role in GAS pathogenesis.

Two group A streptococcal peptide pheromones act through opposing Rgg regulators to control biofilm development

Streptococcus pyogenes (Group A Streptococcus, GAS) is an important human commensal that occasionally causes localized infections and less frequently causes severe invasive disease with high mortality rates. How GAS regulates expression of factors used to colonize the host and avoid immune responses remains poorly understood. Intercellular communication is an important means by which bacteria coordinate gene expression to defend against host assaults and competing bacteria, yet no conserved cell-to-cell signaling system has been elucidated in GAS. Encoded within the GAS genome are four rgg-like genes, two of which (rgg2 and rgg3) have no previously described function. We tested the hypothesis that rgg2 or rgg3 rely on extracellular peptides to control target-gene regulation. We found that Rgg2 and Rgg3 together tightly regulate two linked genes encoding new peptide pheromones. Rgg2 activates transcription of and is required for full induction of the pheromone genes, while Rgg3 plays an antagonistic role and represses pheromone expression. The active pheromone signals, termed SHP2 and SHP3, are short and hydrophobic (DI[I/L]IIVGG), and, though highly similar in sequence, their ability to disrupt Rgg3-DNA complexes were observed to be different, indicating that specificity and differential activation of promoters are characteristics of the Rgg2/3 regulatory circuit. SHP-pheromone signaling requires an intact oligopeptide permease (opp) and a metalloprotease (eep), supporting the model that pro-peptides are secreted, processed to the mature form, and subsequently imported to the cytoplasm to interact directly with the Rgg receptors. At least one consequence of pheromone stimulation of the Rgg2/3 pathway is increased biogenesis of biofilms, which counteracts negative regulation of biofilms by RopB (Rgg1). These data provide the first demonstration that Rgg-dependent quorum sensing functions in GAS and substantiate the role that Rggs play as peptide receptors across the Firmicute phylum.

From transcription to activation: how group A streptococcus, the flesh-eating pathogen, regulates SpeB cysteine protease production

Streptococcal pyrogenic exotoxin B (SpeB) is a protease secreted by group A streptococci and known to degrade a wide range of host and GAS proteins in vitro. Although the role of SpeB in GAS infection is debated, recent evidence has conclusively demonstrated that SpeB is critical for the pathogenesis of severe invasive disease caused by GAS. Genetic inactivation of the speB gene results in significantly decreased virulence in a necrotizing fasciitis model of infection. Production of fully active SpeB by GAS is extremely complex. Following transcription and translation the SpeB protein is secreted as an inactive zymogen, which is autocatalytically processed through a series of intermediates to form an active protease. Each step from transcription to protease activation is tightly controlled and regulated by the bacterial cell reflecting the critical role played by this virulence factor in GAS infection. Here we review the molecular aspects of SpeB production by GAS from transcription to activation and the multiple layers of control involved.

A variable region within the genome of Streptococcus pneumoniae contributes to strain-strain variation in virulence

The bacterial factors responsible for the variation in invasive potential between different clones and serotypes of Streptococcus pneumoniae are largely unknown. Therefore, the isolation of rare serotype 1 carriage strains in Indigenous Australian communities provided a unique opportunity to compare the genomes of non-invasive and invasive isolates of the same serotype in order to identify such factors. The human virulence status of non-invasive, intermediately virulent and highly virulent serotype 1 isolates was reflected in mice and showed that whilst both human non-invasive and highly virulent isolates were able to colonize the murine nasopharynx equally, only the human highly virulent isolates were able to invade and survive in the murine lungs and blood. Genomic sequencing comparisons between these isolates identified 8 regions >1 kb in size that were specific to only the highly virulent isolates, and included a version of the pneumococcal pathogenicity island 1 variable region (PPI-1v), phage-associated adherence factors, transporters and metabolic enzymes. In particular, a phage-associated endolysin, a putative iron/lead permease and an operon within PPI-1v exhibited niche-specific changes in expression that suggest important roles for these genes in the lungs and blood. Moreover, in vivo competition between pneumococci carrying PPI-1v derivatives representing the two identified versions of the region showed that the version of PPI-1v in the highly virulent isolates was more competitive than the version from the less virulent isolates in the nasopharyngeal tissue, blood and lungs. This study is the first to perform genomic comparisons between serotype 1 isolates with distinct virulence profiles that correlate between mice and humans, and has highlighted the important role that hypervariable genomic loci, such as PPI-1v, play in pneumococcal disease. The findings of this study have important implications for understanding the processes that drive progression from colonization to invasive disease and will help direct the development of novel therapeutic strategies.

Naturally occurring single amino acid replacements in a regulatory protein alter streptococcal gene expression and virulence in mice

Infection with different strains of the same species of bacteria often results in vastly different clinical outcomes. Despite extensive investigation, the genetic basis of microbial strain-specific virulence remains poorly understood. Recent whole-genome sequencing has revealed that SNPs are the most prevalent form of genetic diversity among different strains of the same species of bacteria. For invasive serotype M3 group A streptococci (GAS) strains, the gene encoding regulator of proteinase B (RopB) has the highest frequency of SNPs. Here, we have determined that ropB polymorphisms alter RopB function and modulate GAS host-pathogen interactions. Sequencing of ropB in 171 invasive serotype M3 GAS strains identified 19 distinct ropB alleles. Inactivation of the ropB gene in strains producing distinct RopB variants had dramatically divergent effects on GAS global gene expression. Additionally, generation of isoallelic GAS strains differing only by a single amino acid in RopB confirmed that variant proteins affected transcript levels of the gene encoding streptococcal proteinase B, a major RopB-regulated virulence factor. Comparison of parental, RopB-inactivated, and RopB isoallelic strains in mouse infection models demonstrated that ropB polymorphisms influence GAS virulence and disease manifestations. These data detail a paradigm in which unbiased, whole-genome sequence analysis of populations of clinical bacterial isolates creates new avenues of productive investigation into the pathogenesis of common human infections.

Virulence of serotype M3 Group A Streptococcus strains in wax worms (Galleria mellonella larvae)

Group A Streptococcus (GAS) causes human infections that range in severity from pharyngitis ("strep-throat") to necrotizing fasciitis ("flesh-eating disease").  To facilitate investigation of the molecular basis of host-pathogen interactions, infection models capable of rapidly screening for differences in GAS strain virulence are needed.  To this end, we developed a Galleria mellonella larvae (wax worm) model of invasive GAS infection and used it to compare the virulence of serotype M3 GAS strains.  We found that GAS causes severe tissue damage and kills wax worms in a dose-dependent manner.  The virulence of genetically distinct GAS strains was compared by Kaplan-Meier survival analysis and determining 50% lethal doses (LD 50).  Host-pathogen interactions were further characterized using quantitative culture, histopathology and TaqMan assays.  GAS strains known to be highly pathogenic in mice and monkeys caused significantly lower survival and had significantly lower LD 50s in wax worms than GAS strains associated with attenuated virulence or asymptomatic carriage.  Furthermore, isogenic inactivation of proven virulence factors resulted in a significantly increased LD 50 and decreased lesion size compared to the wild-type strain, a finding that also strongly correlates with animal studies.  Importantly, survival analysis and LD 50 determination in wax worms supported our hypothesis that a newly emerged GAS subclone that is epidemiologically associated with more human necrotizing fasciitis cases than its progenitor lineage has significantly increased virulence.  We conclude that GAS virulence in wax worms strongly correlates with the data obtained in vertebrate models, and thus, the Galleria mellonella larva is a useful host organism to study GAS pathogenesis.

The Streptococcus pyogenes proteome: maps, virulence factors and vaccine candidates

Streptococcus pyogenes is an important cause of human morbidity and mortality worldwide. A wealth of genomic information related to this pathogen has facilitated exploration of the proteome, particularly in response to environmental conditions thought to mimic various aspects of pathogenesis. Proteomic approaches are also used to identify immunoreactive proteins for vaccine development and to identify proteins that may induce autoimmunity. These studies have revealed new mechanisms involved in regulating the S. pyogenes proteome, which has opened up new avenues in the study of S. pyogenes pathogenesis. This article describes the methods used, and progress being made towards characterizing the S. pyogenes proteome, including studies seeking to identify potential vaccine candidates.

Parameters governing invasive disease propensity of non-M1 serotype group A streptococci

Group A Streptococcus (GAS) causes rare but life-threatening syndromes of necrotizing fasciitis and toxic shock-like syndrome in humans. The GAS serotype M1T1 clone has globally disseminated, and mutations in the control of virulence regulatory sensor kinase (covRS) operon correlate with severe invasive disease. Here, a cohort of non-M1 GAS was screened to determine whether mutation in covRS triggers systemic dissemination in divergent M serotypes. A GAS disease model defining parameters governing invasive propensity of differing M types is proposed. The vast majority of GAS infection is benign. Nonetheless, many divergent M types possess limited capacity to cause invasive infection. M1T1 GAS readily switch to a covRS mutant form that is neutrophil resistant and frequently associated with systemic infection. Whilst non-M1 GAS are shown in this study to less frequently accumulate covRS mutations in vivo, such mutants are isolated from invasive infections and exhibit neutrophil resistance and enhanced virulence. The reduced capacity of non-M1 GAS to switch to the hypervirulent covRS mutant form provides an explanation for the comparatively less frequent isolation of non-M1 serotypes from invasive human infections.