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Characterization of M-Type-Specific Pilus Expression in Group A Streptococcus. J Bacteriol 2022; 204:e0027022. [PMID: 36286511 PMCID: PMC9664953 DOI: 10.1128/jb.00270-22] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Our ability to characterize how a pathogen infects and causes disease, and consequently our ability to devise approaches to prevent or attenuate such infections, is inhibited by the finding that isolates of a given pathogen often show phenotypic variability, for example, in their ability to adhere to host cells through modulation of cell surface adhesins. Such variability is observed between isolates of group A
Streptococcus
(GAS), and this study investigates the molecular basis for why some GAS isolates produce pili, cell wall-anchored adhesins, in lower abundance than other isolates do.
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2
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Nakata M, Kreikemeyer B. Genetics, Structure, and Function of Group A Streptococcal Pili. Front Microbiol 2021; 12:616508. [PMID: 33633705 PMCID: PMC7900414 DOI: 10.3389/fmicb.2021.616508] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Accepted: 01/18/2021] [Indexed: 12/12/2022] Open
Abstract
Streptococcus pyogenes (Group A Streptococcus; GAS) is an exclusively human pathogen. This bacterial species is responsible for a large variety of infections, ranging from purulent but mostly self-limiting oropharynx/skin diseases to streptococcal sequelae, including glomerulonephritis and rheumatic fever, as well as life-threatening streptococcal toxic-shock syndrome. GAS displays a wide array of surface proteins, with antigenicity of the M protein and pili utilized for M- and T-serotyping, respectively. Since the discovery of GAS pili in 2005, their genetic features, including regulation of expression, and structural features, including assembly mechanisms and protein conformation, as well as their functional role in GAS pathogenesis have been intensively examined. Moreover, their potential as vaccine antigens has been studied in detail. Pilus biogenesis-related genes are located in a discrete section of the GAS genome encoding fibronectin and collagen binding proteins and trypsin-resistant antigens (FCT region). Based on the heterogeneity of genetic composition and DNA sequences, this region is currently classified into nine distinguishable forms. Pili and fibronectin-binding proteins encoded in the FCT region are known to be correlated with infection sites, such as the skin and throat, possibly contributing to tissue tropism. As also found for pili of other Gram-positive bacterial pathogens, GAS pilin proteins polymerize via isopeptide bonds, while intramolecular isopeptide bonds present in the pilin provide increased resistance to degradation by proteases. As supported by findings showing that the main subunit is primarily responsible for T-serotyping antigenicity, pilus functions and gene expression modes are divergent. GAS pili serve as adhesins for tonsillar tissues and keratinocyte cell lines. Of note, a minor subunit is considered to have a harpoon function by which covalent thioester bonds with host ligands are formed. Additionally, GAS pili participate in biofilm formation and evasion of the immune system in a serotype/strain-specific manner. These multiple functions highlight crucial roles of pili during the onset of GAS infection. This review summarizes the current state of the art regarding GAS pili, including a new mode of host-GAS interaction mediated by pili, along with insights into pilus expression in terms of tissue tropism.
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Affiliation(s)
- Masanobu Nakata
- Department of Oral Microbiology, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan
| | - Bernd Kreikemeyer
- Institute of Medical Microbiology, Virology and Hygiene, University of Rostock, Rostock, Germany
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3
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Deciphering Streptococcal Biofilms. Microorganisms 2020; 8:microorganisms8111835. [PMID: 33233415 PMCID: PMC7700319 DOI: 10.3390/microorganisms8111835] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2020] [Revised: 11/10/2020] [Accepted: 11/17/2020] [Indexed: 12/19/2022] Open
Abstract
Streptococci are a diverse group of bacteria, which are mostly commensals but also cause a considerable proportion of life-threatening infections. They colonize many different host niches such as the oral cavity, the respiratory, gastrointestinal, and urogenital tract. While these host compartments impose different environmental conditions, many streptococci form biofilms on mucosal membranes facilitating their prolonged survival. In response to environmental conditions or stimuli, bacteria experience profound physiologic and metabolic changes during biofilm formation. While investigating bacterial cells under planktonic and biofilm conditions, various genes have been identified that are important for the initial step of biofilm formation. Expression patterns of these genes during the transition from planktonic to biofilm growth suggest a highly regulated and complex process. Biofilms as a bacterial survival strategy allow evasion of host immunity and protection against antibiotic therapy. However, the exact mechanisms by which biofilm-associated bacteria cause disease are poorly understood. Therefore, advanced molecular techniques are employed to identify gene(s) or protein(s) as targets for the development of antibiofilm therapeutic approaches. We review our current understanding of biofilm formation in different streptococci and how biofilm production may alter virulence-associated characteristics of these species. In addition, we have summarized the role of surface proteins especially pili proteins in biofilm formation. This review will provide an overview of strategies which may be exploited for developing novel approaches against biofilm-related streptococcal infections.
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4
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Jespersen MG, Lacey JA, Tong SYC, Davies MR. Global genomic epidemiology of Streptococcus pyogenes. INFECTION GENETICS AND EVOLUTION 2020; 86:104609. [PMID: 33147506 DOI: 10.1016/j.meegid.2020.104609] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Revised: 10/20/2020] [Accepted: 10/23/2020] [Indexed: 02/04/2023]
Abstract
Streptococcus pyogenes is one of the Top 10 human infectious disease killers worldwide causing a range of clinical manifestations in humans. Colonizing a range of ecological niches within its sole host, the human, is key to the ability of this opportunistic pathogen to cause direct and post-infectious manifestations. The expansion of genome sequencing capabilities and data availability over the last decade has led to an improved understanding of the evolutionary dynamics of this pathogen within a global framework where epidemiological relationships and evolutionary mechanisms may not be universal. This review uses the recent publication by Davies et al., 2019 as an updated global framework to address S. pyogenes population genomics, highlighting how genomics is being used to gain new insights into evolutionary processes, transmission pathways, and vaccine design.
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Affiliation(s)
- Magnus G Jespersen
- Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
| | - Jake A Lacey
- Doherty Department, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
| | - Steven Y C Tong
- Doherty Department, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia; Victorian Infectious Diseases Service, The Royal Melbourne Hospital, at the Peter Doherty Institute for Infection and Immunity, VIC, Australia
| | - Mark R Davies
- Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia.
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Buckley SJ, Davies MR, McMillan DJ. In silico characterisation of stand-alone response regulators of Streptococcus pyogenes. PLoS One 2020; 15:e0240834. [PMID: 33075055 PMCID: PMC7571705 DOI: 10.1371/journal.pone.0240834] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2020] [Accepted: 10/02/2020] [Indexed: 12/20/2022] Open
Abstract
Bacterial “stand-alone” response regulators (RRs) are pivotal to the control of gene transcription in response to changing cytosolic and extracellular microenvironments during infection. The genome of group A Streptococcus (GAS) encodes more than 30 stand-alone RRs that orchestrate the expression of virulence factors involved in infecting multiple tissues, so causing an array of potentially lethal human diseases. Here, we analysed the molecular epidemiology and biological associations in the coding sequences (CDSs) and upstream intergenic regions (IGRs) of 35 stand-alone RRs from a collection of global GAS genomes. Of the 944 genomes analysed, 97% encoded 32 or more of the 35 tested RRs. The length of RR CDSs ranged from 297 to 1587 nucleotides with an average nucleotide diversity (π) of 0.012, while the IGRs ranged from 51 to 666 nucleotides with average π of 0.017. We present new evidence of recombination in multiple RRs including mga, leading to mga-2 switching, emm-switching and emm-like gene chimerization, and the first instance of an isolate that encodes both mga-1 and mga-2. Recombination was also evident in rofA/nra and msmR loci with 15 emm-types represented in multiple FCT (fibronectin-binding, collagen-binding, T-antigen)-types, including novel emm-type/FCT-type pairings. Strong associations were observed between concatenated RR allele types, and emm-type, MLST-type, core genome phylogroup, and country of sampling. No strong associations were observed between individual loci and disease outcome. We propose that 11 RRs may form part of future refinement of GAS typing systems that reflect core genome evolutionary associations. This subgenomic analysis revealed allelic traits that were informative to the biological function, GAS strain definition, and regional outbreak detection.
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Affiliation(s)
- Sean J. Buckley
- School of Health and Sports Sciences, University of the Sunshine Coast, Sippy Downs, Queensland, Australia
- * E-mail:
| | - Mark R. Davies
- Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
| | - David J. McMillan
- School of Health and Sports Sciences, University of the Sunshine Coast, Sippy Downs, Queensland, Australia
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6
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T4 Pili Promote Colonization and Immune Evasion Phenotypes of Nonencapsulated M4 Streptococcus pyogenes. mBio 2020; 11:mBio.01580-20. [PMID: 32694142 PMCID: PMC7374061 DOI: 10.1128/mbio.01580-20] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Streptococcus pyogenes (group A Streptococcus [GAS]) is an important human pathogen causing a broad spectrum of diseases and associated with significant global morbidity and mortality. Almost all GAS isolates express a surface hyaluronic acid capsule, a virulence determinant that facilitates host colonization and impedes phagocyte killing. However, recent epidemiologic surveillance has reported a sustained increase in both mucosal and invasive infections caused by nonencapsulated GAS, which questions the indispensable role of hyaluronic acid capsule in GAS pathogenesis. In this study, we found that pilus of M4 GAS not only significantly promotes biofilm formation, adherence, and cytotoxicity to human upper respiratory tract epithelial cells and keratinocytes, but also promotes survival in human whole blood and increased virulence in murine models of invasive infection. T4 antigen, the pilus backbone protein of M4 GAS, binds haptoglobin, an abundant human acute-phase protein upregulated upon infection and inflammation, on the bacterial surface. Haptoglobin sequestration reduces the susceptibility of nonencapsulated M4 GAS to antimicrobial peptides released from activated neutrophils and platelets. Our results reveal a previously unappreciated virulence-promoting role of M4 GAS pili, in part mediated by co-opting the biology of haptoglobin to mitigate host antimicrobial defenses.IMPORTANCE Group A Streptococcus (GAS) is a strict human pathogen causing more than 700 million infections globally each year. The majority of the disease-causing GAS are encapsulated, which greatly guarantees survival and dissemination in the host. Emergence of the capsule-negative GAS, such as M4 GAS, in recent epidemiologic surveillance alarms the necessity to elucidate the virulence determinants of these pathogens. Here, we found that M4 pili play an important role in promoting M4 GAS adherence and cytotoxicity to human pharyngeal epithelial cells and keratinocytes. The same molecule also significantly enhanced M4 GAS survival and replication in human whole blood and experimental murine infection. T4 antigen, which composes the backbone of M4 pili, was able to sequester the very abundant serum protein haptoglobin to further confer M4 GAS resistance to antibacterial substances released by neutrophils and platelets.
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Nakata M, Sumitomo T, Patenge N, Kreikemeyer B, Kawabata S. Thermosensitive pilus production by FCT type 3 Streptococcus pyogenes controlled by Nra regulator translational efficiency. Mol Microbiol 2019; 113:173-189. [PMID: 31633834 PMCID: PMC7079067 DOI: 10.1111/mmi.14408] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/19/2019] [Indexed: 01/18/2023]
Abstract
Streptococcus pyogenes produces a diverse variety of pili in a serotype‐dependent manner and thermosensitive expression of pilus biogenesis genes was previously observed in a serotype M49 strain. However, the precise mechanism and biological significance remain unclear. Herein, the pilus expression analysis revealed the thermosensitive pilus production only in strains possessing the transcriptional regulator Nra. Experimental data obtained for nra deletion and conditional nra‐expressing strains in the background of an M49 strain and the Lactococcus heterologous expression system, indicated that Nra is a positive regulator of pilus genes and also highlighted the importance of the level of intracellular Nra for the thermoregulation of pilus expression. While the nra mRNA level was not significantly influenced by a temperature shift, the Nra protein level was concomitantly increased when the culture temperature was decreased. Intriguingly, a putative stem‐loop structure within the coding region of nra mRNA was a factor related to the post‐transcriptional efficiency of nra mRNA translation. Either deletion of the stem‐loop structure or introduction of silent chromosomal mutations designed to melt the structure attenuated Nra levels, resulting in decreased pilus production. Consequently, the temperature‐dependent translational efficacy of nra mRNA influenced pilus thermoregulation, thereby potentially contributing to the fitness of nra‐positive S. pyogenes in human tissues.
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Affiliation(s)
- Masanobu Nakata
- Department of Oral and Molecular Microbiology, Osaka University Graduate School of Dentistry, 1-8, Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Tomoko Sumitomo
- Department of Oral and Molecular Microbiology, Osaka University Graduate School of Dentistry, 1-8, Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Nadja Patenge
- Institute of Medical Microbiology, Virology and Hygiene, University of Rostock, Rostock, D-18057, Germany
| | - Bernd Kreikemeyer
- Institute of Medical Microbiology, Virology and Hygiene, University of Rostock, Rostock, D-18057, Germany
| | - Shigetada Kawabata
- Department of Oral and Molecular Microbiology, Osaka University Graduate School of Dentistry, 1-8, Yamadaoka, Suita, Osaka, 565-0871, Japan
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8
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Abstract
The clinico-epidemiological features of diseases caused by group A streptococci (GAS) is presented through the lens of the ecology, population genetics, and evolution of the organism. The serological targets of three typing schemes (M, T, SOF) are themselves GAS cell surface proteins that have a myriad of virulence functions and a diverse array of structural forms. Horizontal gene transfer expands the GAS antigenic cell surface repertoire by generating numerous combinations of M, T, and SOF antigens. However, horizontal gene transfer of the serotype determinant genes is not unconstrained, and therein lies a genetic organization that may signify adaptations to a narrow ecological niche, such as the primary tissue reservoirs of the human host. Adaptations may be further shaped by selection pressures such as herd immunity. Understanding the molecular evolution of GAS on multiple levels-short, intermediate, and long term-sheds insight on mechanisms of host-pathogen interactions, the emergence and spread of new clones, rational vaccine design, and public health interventions.
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9
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Identification and Characterization of Serotype-Specific Variation in Group A Streptococcus Pilus Expression. Infect Immun 2018; 86:IAI.00792-17. [PMID: 29158432 DOI: 10.1128/iai.00792-17] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2017] [Accepted: 11/13/2017] [Indexed: 12/22/2022] Open
Abstract
Isolates of a given bacterial pathogen often display phenotypic variation, and this can negatively impact public health, for example, by reducing the efficacy of preventative measures. Here, we identify that the human pathogen group A Streptococcus (GAS; Streptococcus pyogenes) expresses pili on its cell surface in a serotype-specific manner. Specifically, we show that serotype M3 GAS isolates, which are nonrandomly associated with causing particularly severe and lethal invasive infections, produce negligible amounts of pili relative to serotype M1 and M49 isolates. Performance of an interserotype transcriptome comparison (serotype M1 versus serotype M3) was instrumental in this discovery. We also identified that the transcriptional regulator Nra positively regulates pilus expression in M3 GAS isolates and that the low level of pilus expression of these isolates correlates with a low level of nra transcription. Finally, we discovered that the phenotypic consequences of low levels of pilus expression by M3 GAS isolates are a reduced ability to adhere to host cells and an increased ability to survive and proliferate in human blood. We propose that an enhanced ability to survive in human blood, in part due to reduced pilus expression, is a contributing factor in the association of serotype M3 isolates with highly invasive infections. In conclusion, our data show that GAS isolates express pili in a serotype-dependent manner and may inform vaccine development, given that pilus proteins are being discussed as possible GAS vaccine antigens.
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10
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Incremental Contributions of FbaA and Other Impetigo-Associated Surface Proteins to Fitness and Virulence of a Classical Group A Streptococcal Skin Strain. Infect Immun 2017; 85:IAI.00374-17. [PMID: 28808160 DOI: 10.1128/iai.00374-17] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Accepted: 08/08/2017] [Indexed: 12/26/2022] Open
Abstract
Group A streptococci (GAS) are highly prevalent human pathogens whose primary ecological niche is the superficial epithelial layers of the throat and/or skin. Many GAS strains with a strong tendency to cause pharyngitis are distinct from strains that tend to cause impetigo; thus, genetic differences between them may confer host tissue-specific virulence. In this study, the FbaA surface protein gene was found to be present in most skin specialist strains but largely absent from a genetically related subset of pharyngitis isolates. In an ΔfbaA mutant constructed in the impetigo strain Alab49, loss of FbaA resulted in a slight but significant decrease in GAS fitness in a humanized mouse model of impetigo; the ΔfbaA mutant also exhibited decreased survival in whole human blood due to phagocytosis. In assays with highly sensitive outcome measures, Alab49ΔfbaA was compared to other isogenic mutants lacking virulence genes known to be disproportionately associated with classical skin strains. FbaA and PAM (i.e., the M53 protein) had additive effects in promoting GAS survival in whole blood. The pilus adhesin tip protein Cpa promoted Alab49 survival in whole blood and appears to fully account for the antiphagocytic effect attributable to pili. The finding that numerous skin strain-associated virulence factors make slight but significant contributions to virulence underscores the incremental contributions to fitness of individual surface protein genes and the multifactorial nature of GAS-host interactions.
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11
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Increased Pilus Production Conferred by a Naturally Occurring Mutation Alters Host-Pathogen Interaction in Favor of Carriage in Streptococcus pyogenes. Infect Immun 2017; 85:IAI.00949-16. [PMID: 28264907 DOI: 10.1128/iai.00949-16] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2016] [Accepted: 02/28/2017] [Indexed: 12/25/2022] Open
Abstract
Studies of the human pathogen group A Streptococcus (GAS) define the carrier phenotype to be an increased ability to adhere to and persist on epithelial surfaces and a decreased ability to cause disease. We tested the hypothesis that a single amino acid change (Arg135Gly) in a highly conserved sensor kinase (LiaS) of a poorly defined GAS regulatory system contributes to a carrier phenotype through increased pilus production. When introduced into an emm serotype-matched invasive strain, the carrier allele (the gene encoding the LiaS protein with an arginine-to-glycine change at position 135 [liaSR135G]) recapitulated a carrier phenotype defined by an increased ability to adhere to mucosal surfaces and a decreased ability to cause disease. Gene transcript analyses revealed that the liaS mutation significantly altered transcription of the genes encoding pilus in the presence of bacitracin. Elimination of pilus production in the isogenic carrier mutant decreased its ability to colonize the mouse nasopharynx and to adhere to and be internalized by cultured human epithelial cells and restored the virulence phenotype in a mouse model of necrotizing fasciitis. We also observed significantly reduced survival of the isogenic carrier mutant compared to that of the parental invasive strain after exposure to human neutrophils. Elimination of pilus in the isogenic carrier mutant increased the level of survival after exposure to human neutrophils to that for the parental invasive strain. Together, our data demonstrate that the carrier mutation (liaSR135G) affects pilus expression. Our data suggest new mechanisms of pilus gene regulation in GAS and that the invasiveness associated with pilus gene regulation in GAS differs from the enhanced invasiveness associated with increased pilus production in other bacterial pathogens.
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12
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Bessen DE. Tissue tropisms in group A Streptococcus: what virulence factors distinguish pharyngitis from impetigo strains? Curr Opin Infect Dis 2016; 29:295-303. [PMID: 26895573 PMCID: PMC5373551 DOI: 10.1097/qco.0000000000000262] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
PURPOSE OF REVIEW Group A streptococci (GAS) are a common cause of pharyngitis and impetigo, and distinct throat strains and skin strains have been long recognized. This review aims to describe recent advances in molecular differences between throat and skin strains, and the pathogenic mechanisms used by virulence factors that may distinguish between these two groups. RECENT FINDINGS Recent findings include a new typing scheme for GAS strains based on sequence clusters of genes encoding the entire surface-exposed portion of M protein; correlations between emm-based typing schemes, clinical disease and surface adhesins; covalent bond formation mediated by GAS pili and other adhesins in binding to host ligands; a key role for superantigens in oropharyngeal infection via binding major histocompatibility complex class II antigen; and migration of GAS-specific Th17 cells from the upper respiratory tract to the brain, which may be relevant to autoimmune sequelae. SUMMARY The gap between molecular markers of disease (correlation) and virulence mechanisms (causation) in the establishment of tissue tropisms for GAS infection currently remains wide, but the gap also continues to narrow. Whole genome sequencing combined with mutant construction and improvements in animal models for oropharyngeal infection by GAS may help pave the way for new discoveries.
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Affiliation(s)
- Debra E Bessen
- Department of Microbiology and Immunology, New York Medical College, New York, USA
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The FasX Small Regulatory RNA Negatively Regulates the Expression of Two Fibronectin-Binding Proteins in Group A Streptococcus. J Bacteriol 2015; 197:3720-30. [PMID: 26391206 DOI: 10.1128/jb.00530-15] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2015] [Accepted: 09/12/2015] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED The group A Streptococcus (GAS; Streptococcus pyogenes) causes more than 700 million human infections each year. The success of this pathogen can be traced in part to the extensive arsenal of virulence factors that are available for expression in temporally and spatially specific manners. To modify the expression of these virulence factors, GAS use both protein- and RNA-based regulators, with the best-characterized RNA-based regulator being the small regulatory RNA (sRNA) FasX. FasX is a 205-nucleotide sRNA that contributes to GAS virulence by enhancing the expression of the thrombolytic secreted virulence factor streptokinase and by repressing the expression of the collagen-binding cell surface pili. Here, we have expanded the FasX regulon, showing that this sRNA also negatively regulates the expression of the adhesion- and internalization-promoting, fibronectin-binding proteins PrtF1 and PrtF2. FasX posttranscriptionally regulates the expression of PrtF1/2 through a mechanism that involves base pairing to the prtF1 and prtF2 mRNAs within their 5' untranslated regions, overlapping the mRNA ribosome-binding sites. Thus, duplex formation between FasX and the prtF1 and prtF2 mRNAs blocks ribosome access, leading to an inhibition of mRNA translation. Given that FasX positively regulates the expression of the spreading factor streptokinase and negatively regulates the expression of the collagen-binding pili and of the fibronectin-binding PrtF1/2, our data are consistent with FasX functioning as a molecular switch that governs the transition of GAS between the colonization and dissemination stages of infection. IMPORTANCE More than half a million deaths each year are a consequence of infections caused by GAS. Insights into how this pathogen regulates the production of proteins during infection may facilitate the development of novel therapeutic or preventative regimens aimed at inhibiting this activity. Here, we have expanded insight into the regulatory activity of the GAS small RNA FasX. In addition to identifying that FasX reduces the abundance of the cell surface-located fibronectin-binding proteins PrtF1/2, fibronectin is present in high abundance in human tissues, and we have determined the mechanism behind this regulation. Importantly, as FasX is the only mechanistically characterized regulatory RNA in GAS, it serves as a model RNA in this and related pathogens.
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14
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Danger JL, Cao TN, Cao TH, Sarkar P, Treviño J, Pflughoeft KJ, Sumby P. The small regulatory RNA FasX enhances group A Streptococcus virulence and inhibits pilus expression via serotype-specific targets. Mol Microbiol 2015; 96:249-62. [PMID: 25586884 DOI: 10.1111/mmi.12935] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/12/2015] [Indexed: 12/31/2022]
Abstract
Bacterial pathogens commonly show intra-species variation in virulence factor expression and often this correlates with pathogenic potential. The group A Streptococcus (GAS) produces a small regulatory RNA (sRNA), FasX, which regulates the expression of pili and the thrombolytic agent streptokinase. As GAS serotypes are polymorphic regarding (a) FasX abundance, (b) the fibronectin, collagen, T-antigen (FCT) region of the genome, which contains the pilus genes (nine different FCT-types), and (c) the streptokinase-encoding gene (ska) sequence (two different alleles), we sought to test whether FasX regulates pilus and streptokinase expression in a serotype-specific manner. Parental, fasX mutant and complemented derivatives of serotype M1 (ska-2, FCT-2), M2 (ska-1, FCT-6), M6 (ska-2, FCT-1) and M28 (ska-1, FCT-4) isolates were compared. While FasX reduced pilus expression in each serotype, the molecular basis differed, as FasX bound, and inhibited the translation of, different FCT-region mRNAs. FasX enhanced streptokinase expression in each serotype, although the degree of regulation varied. Finally, we established that the regulation afforded by FasX enhances GAS virulence, assessed by a model of bacteremia using human plasminogen-expressing mice. Our data are the first to identify and characterize serotype-specific regulation by an sRNA in GAS, and to show an sRNA directly contributes to GAS virulence.
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Affiliation(s)
- Jessica L Danger
- Center for Molecular Medicine, Department of Microbiology & Immunology, University of Nevada, School of Medicine, Reno, Nevada, USA
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15
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Whole-genome association study on tissue tropism phenotypes in group A Streptococcus. J Bacteriol 2011; 193:6651-63. [PMID: 21949075 DOI: 10.1128/jb.05263-11] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Group A Streptococcus (GAS) has a rich evolutionary history of horizontal transfer among its core genes. Yet, despite extensive genetic mixing, GAS strains have discrete ecological phenotypes. To further our understanding of the molecular basis for ecological phenotypes, comparative genomic hybridization of a set of 97 diverse strains to a GAS pangenome microarray was undertaken, and the association of accessory genes with emm genotypes that define tissue tropisms for infection was determined. Of the 22 nonprophage accessory gene regions (AGRs) identified, only 3 account for all statistically significant linkage disequilibrium among strains having the genotypic biomarkers for throat versus skin infection specialists. Networked evolution and population structure analyses of loci representing each of the AGRs reveal that most strains with the skin specialist and generalist biomarkers form discrete clusters, whereas strains with the throat specialist biomarker are highly diverse. To identify coinherited and coselected accessory genes, the strength of genetic associations was determined for all possible pairwise combinations of accessory genes among the 97 GAS strains. Accessory genes showing very strong associations provide the basis for an evolutionary model, which reveals that a major transition between many throat and skin specialist haplotypes correlates with the gain or loss of genes encoding fibronectin-binding proteins. This study employs a novel synthesis of tools to help delineate the major genetic changes associated with key adaptive shifts in an extensively recombined bacterial species.
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16
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Ouyang Z, Deka RK, Norgard MV. BosR (BB0647) controls the RpoN-RpoS regulatory pathway and virulence expression in Borrelia burgdorferi by a novel DNA-binding mechanism. PLoS Pathog 2011; 7:e1001272. [PMID: 21347346 PMCID: PMC3037356 DOI: 10.1371/journal.ppat.1001272] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2010] [Accepted: 01/06/2011] [Indexed: 11/29/2022] Open
Abstract
In Borrelia burgdorferi (Bb), the Lyme disease spirochete, the alternative σ factor σ54 (RpoN) directly activates transcription of another alternative σ factor, σS (RpoS) which, in turn, controls the expression of virulence-associated membrane lipoproteins. As is customary in σ54-dependent gene control, a putative NtrC-like enhancer-binding protein, Rrp2, is required to activate the RpoN-RpoS pathway. However, recently it was found that rpoS transcription in Bb also requires another regulator, BosR, which was previously designated as a Fur or PerR homolog. Given this unexpected requirement for a second activator to promote σ54-dependent gene transcription, and the fact that regulatory mechanisms among similar species of pathogenic bacteria can be strain-specific, we sought to confirm the regulatory role of BosR in a second virulent strain (strain 297) of Bb. Indeed, BosR displayed the same influence over lipoprotein expression and mammalian infectivity for strain Bb 297 that were previously noted for Bb strain B31. We subsequently found that recombinant BosR (rBosR) bound to the rpoS gene at three distinct sites, and that binding occurred despite the absence of consensus Fur or Per boxes. This led to the identification of a novel direct repeat sequence (TAAATTAAAT) critical for rBosR binding in vitro. Mutations in the repeat sequence markedly inhibited or abolished rBosR binding. Taken together, our studies provide new mechanistic insights into how BosR likely acts directly on rpoS as a positive transcriptional activator. Additional novelty is engendered by the facts that, although BosR is a Fur or PerR homolog and it contains zinc (like Fur and PerR), it has other unique features that clearly set it apart from these other regulators. Our findings also have broader implications regarding a previously unappreciated layer of control that can be involved in σ54–dependent gene regulation in bacteria. Lyme disease, caused by the bacterium Borrelia burgdorferi (Bb), remains the most common arthropod-borne illness in the United States. A critical strategy for Bb to maintain its presence in nature is adaptation to its diverse tick and mammalian (mouse) hosts. To accomplish this, Bb encodes a potential gene regulator, BB0647 (BosR). Herein, we confirmed that BosR is essential for Bb to establish mammalian infection. We then found that purified recombinant BosR bound to the promoter DNA (regulatory region) of rpoS, suggesting that BosR directly controls the expression of the rpoS gene. This study has revealed a new mechanism of bacterial gene control. The discovery that BosR governs Bb's virulence may lead to new strategies to interrupt the bacterium's complex life cycle.
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Affiliation(s)
- Zhiming Ouyang
- Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Ranjit K. Deka
- Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Michael V. Norgard
- Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- * E-mail:
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Manetti AGO, Köller T, Becherelli M, Buccato S, Kreikemeyer B, Podbielski A, Grandi G, Margarit I. Environmental acidification drives S. pyogenes pilus expression and microcolony formation on epithelial cells in a FCT-dependent manner. PLoS One 2010; 5:e13864. [PMID: 21079780 PMCID: PMC2974651 DOI: 10.1371/journal.pone.0013864] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2010] [Accepted: 10/18/2010] [Indexed: 01/24/2023] Open
Abstract
Group A Streptococcus (GAS, Streptococcus pyogenes) is a Gram-positive human pathogen responsible for a diverse variety of diseases, including pharyngitis, skin infections, invasive necrotizing fasciitis and autoimmune sequelae. We have recently shown that GAS cell adhesion and biofilm formation is associated with the presence of pili on the surface of these bacteria. GAS pilus proteins are encoded in the FCT (Fibronectin- Collagen-T antigen) genomic region, of which nine different variants have been identified so far. In the present study we undertook a global analysis of GAS isolates representing the majority of FCT-variants to investigate the effect of environmental growth conditions on their capacity to form multicellular communities. For FCT-types 2, 3, 5 and 6 and a subset of FCT-4 strains, we observed that acidification resulting from fermentative sugar metabolism leads to an increased ability of the bacteria to form biofilm on abiotic surfaces and microcolonies on epithelial cells. The higher biofilm forming capacity at low environmental pH was directly associated with an enhanced expression of the genes encoding the pilus components and of their transcription regulators. The data indicate that environmental pH affects the expression of most pilus types and thereby the formation of multicellular cell-adhering communities that assist the initial steps of GAS infection.
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Affiliation(s)
| | - Thomas Köller
- Institute of Medical Microbiology, Virology and Hygiene, Rostock, Germany
| | | | | | - Bernd Kreikemeyer
- Institute of Medical Microbiology, Virology and Hygiene, Rostock, Germany
| | - Andreas Podbielski
- Institute of Medical Microbiology, Virology and Hygiene, Rostock, Germany
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18
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Abstract
Group A Streptococcus (GAS) is a human-specific pathogen that is highly prevalent throughout the world. The vast majority of GAS infections lead to a mild disease involving the epithelial surfaces of either the throat or skin. The concept of distinct sets of 'throat' and 'skin' strains of GAS has long been conceived. From an ecological standpoint, the epithelium of the throat and skin are important because it is where the organism is most successful in reproducing and transmitting to new hosts. This article examines key features of the epidemiology, population biology and molecular pathogenesis that underlie the tissue site preferences for infection exhibited by GAS, with an emphasis on work from our laboratory on skin tropisms. Recombinational replacement with orthologous gene forms, following interspecies transfer, appears to be an important genetic step leading up to the exploitation of new niches by GAS.
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Affiliation(s)
- Debra E Bessen
- Department of Microbiology & Immunology, New York Medical College, Valhalla, NY 10573, USA, Tel.: +1 914 594 4193, Fax: +1 914 594 4176
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Sugareva V, Arlt R, Fiedler T, Riani C, Podbielski A, Kreikemeyer B. Serotype- and strain- dependent contribution of the sensor kinase CovS of the CovRS two-component system to Streptococcus pyogenes pathogenesis. BMC Microbiol 2010; 10:34. [PMID: 20113532 PMCID: PMC2823723 DOI: 10.1186/1471-2180-10-34] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2009] [Accepted: 02/01/2010] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND The Streptococcus pyogenes (group A streptococci, GAS) two-component signal transduction system CovRS has been described to be important for pathogenesis of this exclusively human bacterial species. If this system acts uniquely in all serotypes is currently unclear. Presence of serotype- or strain-dependent regulatory circuits and polarity is an emerging scheme in Streptococcus pyogenes pathogenesis. Thus, the contribution of the sensor kinase (CovS) of the global regulatory two-component signal transduction system CovRS on pathogenesis of several M serotypes was investigated. RESULTS CovS mutation uniformly repressed capsule expression and hampered keratinocyte adherence in all tested serotypes. However, a serotype- and even strain-dependent contribution on survival in whole human blood and biofilm formation was noted, respectively. CONCLUSIONS These data provide new information on the action of the CovS sensor kinase and revealed that its activity on capsule expression and keratinocyte adherence is uniform across serotypes, whereas the influence on biofilm formation and blood survival is serotype or even strain dependent. This adds the CovRS system to a growing list of serotype-specific acting regulatory loci in S. pyogenes.
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Affiliation(s)
- Venelina Sugareva
- University of Rostock, Medical Faculty, Institute of Medical Microbiology, Virology and Hygiene, Department of Med, Microbiology and Hospital Hygiene, Schillingallee 70, 18055 Rostock, Germany
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20
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Streptococcus pyogenes CovRS mediates growth in iron starvation and in the presence of the human cationic antimicrobial peptide LL-37. J Bacteriol 2008; 191:673-7. [PMID: 18996992 DOI: 10.1128/jb.01256-08] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
We found that the global regulatory two-component signal transduction system CovRS mediates the ability of group A streptococcus (GAS) to grow under two stresses encountered during infection: iron starvation and the presence of LL-37. We also showed that CovRS regulates transcription of the multimetal transporter operon that is important for GAS growth in a low concentration of iron.
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Siller M, Janapatla RP, Pirzada ZA, Hassler C, Zinkl D, Charpentier E. Functional analysis of the group A streptococcal luxS/AI-2 system in metabolism, adaptation to stress and interaction with host cells. BMC Microbiol 2008; 8:188. [PMID: 18973658 PMCID: PMC2603038 DOI: 10.1186/1471-2180-8-188] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2008] [Accepted: 10/30/2008] [Indexed: 01/03/2023] Open
Abstract
Background The luxS/AI-2 signaling pathway has been reported to interfere with important physiological and pathogenic functions in a variety of bacteria. In the present study, we investigated the functional role of the streptococcal luxS/AI-2 system in metabolism and diverse aspects of pathogenicity including the adaptation of the organism to stress conditions using two serotypes of Streptococcus pyogenes, M1 and M19. Results Exposing wild-type and isogenic luxS-deficient strains to sulfur-limited media suggested a limited role for luxS in streptococcal activated methyl cycle metabolism. Interestingly, loss of luxS led to an increased acid tolerance in both serotypes. Accordingly, luxS expression and AI-2 production were reduced at lower pH, thus linking the luxS/AI-2 system to stress adaptation in S. pyogenes. luxS expression and AI-2 production also decreased when cells were grown in RPMI medium supplemented with 10% serum, considered to be a host environment-mimicking medium. Furthermore, interaction analysis with epithelial cells and macrophages showed a clear advantage of the luxS-deficient mutants to be internalized and survive intracellularly in the host cells compared to the wild-type parents. In addition, our data revealed that luxS influences the expression of two virulence-associated factors, the fasX regulatory RNA and the virulence gene sibA (psp). Conclusion Here, we suggest that the group A streptococcal luxS/AI-2 system is not only involved in the regulation of virulence factor expression but in addition low level of luxS expression seems to provide an advantage for bacterial survival in conditions that can be encountered during infections.
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Affiliation(s)
- Maria Siller
- University of Vienna, Department of Microbiology and Immunobiology, 1030 Vienna, Austria.
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Lizano S, Luo F, Tengra FK, Bessen DE. Impact of orthologous gene replacement on the circuitry governing pilus gene transcription in streptococci. PLoS One 2008; 3:e3450. [PMID: 18941636 PMCID: PMC2565503 DOI: 10.1371/journal.pone.0003450] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2008] [Accepted: 09/23/2008] [Indexed: 01/31/2023] Open
Abstract
Background The evolutionary history of several genes of the bacterial pathogen Streptococcus pyogenes strongly suggests an origin in another species, acquired via replacement of the counterpart gene (ortholog) following a recombination event. An example of orthologous gene replacement is provided by the nra/rofA locus, which encodes a key regulator of pilus gene transcription. Of biological importance is the previous finding that the presence of the nra- and rofA-lineage alleles, which are ∼35% divergent, correlates strongly with genetic markers for streptococcal infection at different tissue sites in the human host (skin, throat). Methodology/Principal Findings In this report, the impact of orthologous gene replacement targeting the nra/rofA locus is experimentally addressed. Replacement of the native nra-lineage allele with a rofA-lineage allele, plus their respective upstream regions, preserved the polarity of Nra effects on pilus gene transcription (i.e., activation) in the skin strain Alab49. Increased pilus gene transcription in the rofA chimera correlated with a higher rate of bacterial growth at the skin. The transcriptional regulator MsmR, which represses nra and pilus gene transcription in the Alab49 parent strain, has a slight activating effect on pilus gene expression in the rofA chimera construct. Conclusions/Significance Data show that exchange of orthologous forms of a regulatory gene is stable and robust, and pathogenicity is preserved. Yet, new phenotypes may also be introduced by altering the circuitry within a complex transcriptional regulatory network. It is proposed that orthologous gene replacement via interspecies exchange is an important mechanism in the evolution of highly recombining bacteria such as S. pyogenes.
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Affiliation(s)
- Sergio Lizano
- Department of Microbiology and Immunology, New York Medical College, Valhalla, New York, United States of America
| | - Feng Luo
- Department of Microbiology and Immunology, New York Medical College, Valhalla, New York, United States of America
| | - Farah K. Tengra
- Department of Microbiology and Immunology, New York Medical College, Valhalla, New York, United States of America
| | - Debra E. Bessen
- Department of Microbiology and Immunology, New York Medical College, Valhalla, New York, United States of America
- * E-mail:
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Mode of expression and functional characterization of FCT-3 pilus region-encoded proteins in Streptococcus pyogenes serotype M49. Infect Immun 2008; 77:32-44. [PMID: 18852238 DOI: 10.1128/iai.00772-08] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human pathogen Streptococcus pyogenes (group A streptococcus [GAS]) pilus components, suggested to play a role in pathogenesis, are encoded in the variable FCT (fibronectin- and collagen-binding T-antigen) region. We investigated the functions of sortase A (SrtA), sortase C2 (SrtC2), and the FctA protein of the most prevalent type 3 FCT region from a serotype M49 strain. Although it is considered a housekeeping sortase, SrtA's activity is involved in pilus formation in addition to its essentiality for GAS extracellular matrix protein binding, host cell adherence/internalization, survival in human blood, and biofilm formation. SrtC2 activity is crucial for pilus formation but dispensable for the other phenotypes tested in vitro. FctA is the major pilus backbone protein, simultaneously acting as the M49 T antigen, and requires SrtC2 and LepA, a signal peptidase I homologue, for monomeric surface expression and polymerization, respectively. Collagen-binding protein Cpa expression supports pilus formation at the pilus base. Immunofluorescence microscopy and fluorescence-activated cell sorting analysis revealed several unexpected expression patterns, as follows: (i) the monomeric pilus protein FctA was found exclusively at the old poles of GAS cells, (ii) FctA protein expression increased with lower temperatures, and (iii) FctA protein expression was restricted to 20 to 50% of a given GAS M49 population, suggesting regulation by a bistability mode. Notably, disruption of pilus assembly by sortase deletion rendered GAS serotype M49 significantly more aggressive in a dermonecrotic mouse infection model, indicating that sortase activity and, consequently, pilus expression allow a subpopulation of this GAS serotype to be less aggressive. Thus, pilus expression may not be a virulence attribute of GAS per se.
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Luo F, Lizano S, Banik S, Zhang H, Bessen DE. Role of Mga in group A streptococcal infection at the skin epithelium. Microb Pathog 2008; 45:217-24. [PMID: 18588968 PMCID: PMC2593622 DOI: 10.1016/j.micpath.2008.05.009] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2008] [Revised: 05/26/2008] [Accepted: 05/27/2008] [Indexed: 01/26/2023]
Abstract
Group A streptococci (GAS) primarily cause infection at epithelial tissue sites of its human host. The role of the transcriptional regulator Mga in a humanized mouse model for superficial skin infection was investigated. Inactivation of mga in a skin strain (Alab49) led to loss of virulence. The Deltamga mutant displayed >100-fold decrease in emm (pam) transcript levels, and loss of bacterial-bound plasmin activity. A slight decrease in speB transcription, accompanied by a partial decrease in cysteine protease activity but no change in PrtF2 degradation, was also observed. Mga had no effect on transcription of nra, Nra-regulated pilus genes (cpa, fctA) or other FCT-region genes (msmR, prtF2). Combined with findings on other Alab49 mutants, data show that several essential virulence genes are regulated by Mga or Nra, but not both, implying that any coordinated response during skin infection likely operates at a higher level of transcriptional control. Mga was required for bacterial autoaggregation and biofilm-like growth on an abiotic surface; however, aggregation and biofilm formation have only partial overlap with the skin virulence phenotype. Findings on numerous phenotypes for 7 mutants constructed on the same genetic background yield a detailed, integrated model for GAS pathogenesis at the skin.
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Affiliation(s)
- Feng Luo
- Department of Microbiology and Immunology, New York Medical College, Valhalla, NY, USA
| | - Sergio Lizano
- Department of Microbiology and Immunology, New York Medical College, Valhalla, NY, USA
| | - Sukalyani Banik
- Department of Microbiology and Immunology, New York Medical College, Valhalla, NY, USA
| | - Hong Zhang
- Department of Microbiology and Immunology, New York Medical College, Valhalla, NY, USA
| | - Debra E. Bessen
- Department of Microbiology and Immunology, New York Medical College, Valhalla, NY, USA
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