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Turner CE, Holden MTG, Blane B, Horner C, Peacock SJ, Sriskandan S. The Emergence of Successful Streptococcus pyogenes Lineages through Convergent Pathways of Capsule Loss and Recombination Directing High Toxin Expression. mBio 2019; 10:e02521-19. [PMID: 31822586 PMCID: PMC6904876 DOI: 10.1128/mbio.02521-19] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Accepted: 10/29/2019] [Indexed: 12/17/2022] Open
Abstract
Gene transfer and homologous recombination in Streptococcus pyogenes has the potential to trigger the emergence of pandemic lineages, as exemplified by lineages of emm1 and emm89 that emerged in the 1980s and 2000s, respectively. Although near-identical replacement gene transfer events in the nga (NADase) and slo (streptolysin O) loci conferring high expression of these toxins underpinned the success of these lineages, extension to other emm genotype lineages is unreported. The emergent emm89 lineage was characterized by five regions of homologous recombination additional to nga-slo, including complete loss of the hyaluronic acid capsule synthesis locus hasABC, a genetic trait replicated in two other leading emm types and recapitulated by other emm types by inactivating mutations. We hypothesized that other leading genotypes may have undergone similar recombination events. We analyzed a longitudinal data set of genomes from 344 clinical invasive disease isolates representative of locations across England, dating from 2001 to 2011, and an international collection of S. pyogenes genomes representing 54 different genotypes and found frequent evidence of recombination events at the nga-slo locus predicted to confer higher toxin genotype. We identified multiple associations between recombination at this locus and inactivating mutations within hasAB, suggesting convergent evolutionary pathways in successful genotypes. This included common genotypes emm28 and emm87. The combination of no or low capsule and high expression of nga and slo may underpin the success of many emergent S. pyogenes lineages of different genotypes, triggering new pandemics, and could change the way S. pyogenes causes disease.IMPORTANCEStreptococcus pyogenes is a genetically diverse pathogen, with over 200 different genotypes defined by emm typing, but only a minority of these genotypes are responsible for the majority of human infection in high-income countries. Two prevalent genotypes associated with disease rose to international dominance following recombination of a toxin locus that conferred increased expression. Here, we found that recombination of this locus and promoter has occurred in other diverse genotypes, events that may allow these genotypes to expand in the population. We identified an association between the loss of hyaluronic acid capsule synthesis and high toxin expression, which we propose may be associated with an adaptive advantage. As S. pyogenes pathogenesis depends both on capsule and toxin production, new variants with altered expression may result in abrupt changes in the molecular epidemiology of this pathogen in the human population over time.
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Affiliation(s)
- Claire E Turner
- Molecular Biology & Biotechnology, The Florey Institute, University of Sheffield, Sheffield, United Kingdom
- Department of Infectious Disease, Imperial College London, London, United Kingdom
| | - Matthew T G Holden
- Pathogen Genomics, The Wellcome Trust Sanger Institute, Cambridge, United Kingdom
- School of Medicine, University of St Andrews, St Andrews, United Kingdom
| | - Beth Blane
- Department of Medicine, University of Cambridge, Cambridge, United Kingdom
| | - Carolyne Horner
- British Society for Antimicrobial Chemotherapy, Birmingham, United Kingdom
| | - Sharon J Peacock
- Department of Medicine, University of Cambridge, Cambridge, United Kingdom
| | - Shiranee Sriskandan
- Department of Infectious Disease, Imperial College London, London, United Kingdom
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Flores AR, McNeil JC, Shah B, Van Beneden C, Shelburne SA. Capsule-Negative emm Types Are an Increasing Cause of Pediatric Group A Streptococcal Infections at a Large Pediatric Hospital in Texas. J Pediatric Infect Dis Soc 2019; 8:244-250. [PMID: 30085121 PMCID: PMC8938855 DOI: 10.1093/jpids/piy053] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Accepted: 05/25/2018] [Indexed: 11/13/2022]
Abstract
BACKGROUND Bacterial infections caused by group A Streptococcus (GAS) are common in childhood. Few study reports have provided data on pediatric-specific trends in the epidemiology and bacterial strain characteristics of GAS infections. METHODS We prospectively collected GAS isolates from the clinical microbiology laboratory at Texas Children's Hospital between July 1, 2013, and June 30, 2017. Patient characteristics and GAS disease categories were determined through chart review. GAS isolates were obtained from patients in either the inpatient or outpatient setting, and cases were defined as pharyngeal disease, skin and soft-tissue infection (SSTI), or invasive disease on the basis of predefined criteria. All isolates were emm typed to determine trends over time. RESULTS We identified 930 cases over the 4-year period, including 432 (46.4%) pharyngeal, 235 (25.3%) SSTI, and 263 (28.3%) invasive disease types. The most frequently encountered emm types were emm1 (21.4%), emm12 (15.7%), emm89 (14.6%), emm4 (9.2%), and emm3 (8.2%). We observed significant changes over the 4-year period in the relative frequency of infections caused by emm1 (-17.7%; P = .046), emm4 (8.7%; P = .023), or emm6 (-7.9%; P = .024). Using bioinformatic analyses and targeted gene sequencing, we also discovered that all GAS emm28 and emm87 types harbored mutations that rendered them incapable of producing capsule. The relative frequency of GAS disease cases caused by capsule-negative GAS emm types (emm4, emm22, emm28, emm87, and emm89) increased over the 4-year period (32.2%-44.4%), although the difference was statistically significant for only nonpharyngeal disease types (27.1%-43.9%; P = .038). CONCLUSIONS Our data suggest an evolving epidemiology of GAS in the Houston pediatric population characterized by an increase in the frequency of capsule-negative emm types.
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Affiliation(s)
- Anthony R. Flores
- Division of Infectious Diseases, Department of Pediatrics, Center for Antimicrobial Resistance and Microbial Genomics, McGovern Medical School, University of Texas Health Sciences Center at Houston
| | - J. Chase McNeil
- Section of Infectious Diseases, Department of Pediatrics, Baylor College of Medicine and Texas Children’s Hospital, Houston
| | - Brittany Shah
- Division of Infectious Diseases, Department of Pediatrics, Center for Antimicrobial Resistance and Microbial Genomics, McGovern Medical School, University of Texas Health Sciences Center at Houston
| | - Chris Van Beneden
- Respiratory Diseases Branch, Division of Bacterial Diseases, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia
| | - Samuel A. Shelburne
- Division of Internal Medicine, Departments of Infectious Diseases and Genomic Medicine, MD Anderson Cancer Center, Houston, Texas
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Nye TM, Jacob KM, Holley EK, Nevarez JM, Dawid S, Simmons LA, Watson ME. DNA methylation from a Type I restriction modification system influences gene expression and virulence in Streptococcus pyogenes. PLoS Pathog 2019; 15:e1007841. [PMID: 31206562 PMCID: PMC6597129 DOI: 10.1371/journal.ppat.1007841] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2019] [Revised: 06/27/2019] [Accepted: 05/14/2019] [Indexed: 11/26/2022] Open
Abstract
DNA methylation is pervasive across all domains of life. In bacteria, the presence of N6-methyladenosine (m6A) has been detected among diverse species, yet the contribution of m6A to the regulation of gene expression is unclear in many organisms. Here we investigated the impact of DNA methylation on gene expression and virulence within the human pathogen Streptococcus pyogenes, or Group A Streptococcus. Single Molecule Real-Time sequencing and subsequent methylation analysis identified 412 putative m6A sites throughout the 1.8 Mb genome. Deletion of the Restriction, Specificity, and Methylation gene subunits (ΔRSM strain) of a putative Type I restriction modification system lost all detectable m6A at the recognition sites and failed to prevent transformation with foreign-methylated DNA. RNA-sequencing identified 20 genes out of 1,895 predicted coding regions with significantly different gene expression. All of the differentially expressed genes were down regulated in the ΔRSM strain relative to the parent strain. Importantly, we found that the presence of m6A DNA modifications affected expression of Mga, a master transcriptional regulator for multiple virulence genes, surface adhesins, and immune-evasion factors in S. pyogenes. Using a murine subcutaneous infection model, mice infected with the ΔRSM strain exhibited an enhanced host immune response with larger skin lesions and increased levels of pro-inflammatory cytokines compared to mice infected with the parent or complemented mutant strains, suggesting alterations in m6A methylation influence virulence. Further, we found that the ΔRSM strain showed poor survival within human neutrophils and reduced adherence to human epithelial cells. These results demonstrate that, in addition to restriction of foreign DNA, gram-positive bacteria also use restriction modification systems to regulate the expression of gene networks important for virulence. DNA methylation is common among many bacterial species, yet the contribution of DNA methylation to the regulation of gene expression is unclear outside of a limited number of gram-negative species. We characterized sites of DNA methylation throughout the genome of the gram-positive pathogen Streptococcus pyogenes or Group A Streptococcus. We determined that the gene products of a functional restriction modification system are responsible for genome-wide m6A. The mutant strain lacking DNA methylation showed altered gene expression compared to the parent strain, with several genes important for causing human disease down regulated. Furthermore, we showed that the mutant strain lacking DNA methylation exhibited altered virulence properties compared to the parent strain using various models of pathogenesis. The mutant strain was attenuated for both survival within human neutrophils and adherence to human epithelial cells, and was unable to suppress the host immune response in a murine subcutaneous infection model. Together, these results show that bacterial m6A contributes to differential gene expression and influences the ability of Group A Streptococcus to cause disease. DNA methylation is a conserved feature among bacteria and may represent a potential target for intervention in effort to interfere with the ability of bacteria to cause human disease.
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Affiliation(s)
- Taylor M. Nye
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, United States of America
| | - Kristin M. Jacob
- Division of Pediatric Infectious Diseases, Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, MI, United States of America
| | - Elena K. Holley
- Division of Pediatric Infectious Diseases, Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, MI, United States of America
| | - Juan M. Nevarez
- Division of Pediatric Infectious Diseases, Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, MI, United States of America
| | - Suzanne Dawid
- Division of Pediatric Infectious Diseases, Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, MI, United States of America
| | - Lyle A. Simmons
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, United States of America
| | - Michael E. Watson
- Division of Pediatric Infectious Diseases, Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, MI, United States of America
- * E-mail:
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Wholey WY, Abu-Khdeir M, Yu EA, Siddiqui S, Esimai O, Dawid S. Characterization of the Competitive Pneumocin Peptides of Streptococcus pneumoniae. Front Cell Infect Microbiol 2019; 9:55. [PMID: 30915281 PMCID: PMC6422914 DOI: 10.3389/fcimb.2019.00055] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2018] [Accepted: 02/20/2019] [Indexed: 01/01/2023] Open
Abstract
In the polymicrobial environment of the human nasopharynx, Streptococcus pneumoniae (pneumococcus) competes with other members of the microbial community for limited nutrients in part by secreting small peptide bacteriocins called pneumocins. Pneumocin production is controlled by a quorum sensing system encoded by the blp locus. Although the locus is found in all pneumococci, there is significant variability in the repertoire of pneumocins and associated immunity proteins encoded in the Bacteriocin Immunity Region (BIR) and in the presence or absence of a functional Blp transporter. Strains without an active Blp transporter are inactive in plate overlay assays and rely on a homologous transporter that is only produced during brief periods of competence to stimulate the blp locus and secrete pneumocins. The variability of the locus suggests that selective pressure is influencing the content to promote the optimal competitive environment. Much of the variability in the blp locus has been described at the genome level; the phenotypic activity attributable to the various BIR genes has not been fully described. To examine the role of the predicted pneumocin peptides in competition, 454 isolates were screened for competence independent blp pheromone secretion using plate assays. Active strains were characterized for inhibition, BIR content, BlpC pherotype and serotype. Deletion analysis on inhibitory strains demonstrated that BlpI and BlpJ peptides function as a two-peptide bacteriocin and that BlpIJ immunity is encoded by the co-transcribed blpU4/5 genes. BlpIJ secretion promotes inhibitory activity against the majority of pneumococcal isolates when expressed in a Blp transporter intact background. Intermediate levels of competition in biofilms were noted when BlpIJ containing strains carried the non-functional Blp transporter. Based on genome data, the combination of BlpIJ in a Blp transporter intact strain is surprisingly rare, despite clear advantages during colonization and biofilm growth. In contrast, we show that the blpK/pncF operon encoding the single-peptide pneumocin BlpK and its immunity protein is found in the majority of isolates. Unlike, BlpIJ and BlpK were shown to promote a limited spectrum of inhibition due in part to immunity that is independent of activation of the blp locus.
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Affiliation(s)
- Wei-Yun Wholey
- Department of Pediatrics and Communicable Diseases, University of Michigan Medical School, Ann Arbor, MI, United States
| | - Maha Abu-Khdeir
- Department of Pediatrics and Communicable Diseases, University of Michigan Medical School, Ann Arbor, MI, United States
| | - Emily A Yu
- Department of Pediatrics and Communicable Diseases, University of Michigan Medical School, Ann Arbor, MI, United States
| | - Saher Siddiqui
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI, United States
| | - Ogenna Esimai
- Department of Computer Science and Engineering, University of Texas at Arlington, Arlington, TX, United States
| | - Suzanne Dawid
- Department of Pediatrics and Communicable Diseases, University of Michigan Medical School, Ann Arbor, MI, United States.,Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI, United States
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Virulence Role of the GlcNAc Side Chain of the Lancefield Cell Wall Carbohydrate Antigen in Non-M1-Serotype Group A Streptococcus. mBio 2018; 9:mBio.02294-17. [PMID: 29382733 PMCID: PMC5790915 DOI: 10.1128/mbio.02294-17] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Classification of streptococci is based upon expression of unique cell wall carbohydrate antigens. All serotypes of group A Streptococcus (GAS; Streptococcus pyogenes), a leading cause of infection-related mortality worldwide, express the group A carbohydrate (GAC). GAC, the classical Lancefield antigen, is comprised of a polyrhamnose backbone with N-acetylglucosamine (GlcNAc) side chains. The immunodominant GlcNAc epitope of GAC is the basis of all rapid diagnostic testing for GAS infection. We previously identified the 12-gene GAC biosynthesis gene cluster and determined that the glycosyltransferase GacI was required for addition of the GlcNAc side chain to the polyrhamnose core. Loss of the GAC GlcNAc epitope in serotype M1 GAS resulted in attenuated virulence in two animal infection models and increased GAS sensitivity to killing by whole human blood, serum, neutrophils, and antimicrobial peptides. Here, we report that the GAC biosynthesis gene cluster is ubiquitous among 520 GAS isolates from global sources, representing 105 GAS emm serotypes. Isogenic ΔgacI mutants were constructed in M2, M3, M4, M28, and M89 backgrounds and displayed an array of phenotypes in susceptibility to killing by whole human blood, baby rabbit serum, human platelet releasate, human neutrophils, and antimicrobial peptide LL-37. The contribution of the GlcNAc side chain to GAS survival in vivo also varied by strain, demonstrating that it is not a prerequisite for virulence in the murine infection model. Thus, the relative contribution of GAC to virulence in non-M1 serotypes appears to depend on the quorum of other virulence factors that each strain possesses.IMPORTANCE The Lancefield group A carbohydrate (GAC) is the species-defining antigen for group A Streptococcus (GAS), comprising ~50% of the cell wall of this major human pathogen. We previously showed that the GlcNAc side chain of GAC contributes to the innate immune resistance and animal virulence phenotypes of the globally disseminated strain of serotype M1 GAS. Here, we use isogenic mutagenesis to examine the role of GAC GlcNAc in five additional medically relevant GAS serotypes. Overall, the GlcNAc side chain of GAC contributes to the innate immune resistance of GAS, but the relative contribution varies among individual strains. Moreover, the GAC GlcNAc side chain is not a universal prerequisite for GAS virulence in the animal model.
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