scholarly journals The Emergence of Successful Streptococcus pyogenes Lineages through Convergent Pathways of Capsule Loss and Recombination Directing High Toxin Expression

mBio ◽  
2019 ◽  
Vol 10 (6) ◽  
Author(s):  
Claire E. Turner ◽  
Matthew T. G. Holden ◽  
Beth Blane ◽  
Carolyne Horner ◽  
Sharon J. Peacock ◽  
...  

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. IMPORTANCE Streptococcus 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.

2019 ◽  
Author(s):  
Claire E. Turner ◽  
Matthew T. G. Holden ◽  
Beth Blane ◽  
Carolyne Horner ◽  
Sharon J. Peacock ◽  
...  

AbstractGene transfer and homologous recombination inStreptococcus pyogeneshas the potential to trigger the emergence of pandemic lineages, as exemplified by lineages ofemm1 andemm89 that emerged in the 1980s and 2000s respectively. Although near-identical replacement gene transfer events in thenga(NADase) andslo(Streptolysin O) locus conferring high expression of these toxins underpinned the success of these lineages, extension to otheremm-genotype lineages is unreported. The emergentemm89 lineage was characterised by five regions of homologous recombination additional tonga/slo, including complete loss of the hyaluronic acid capsule synthesis locushasABC,a genetic trait replicated in two other leadingemmtypes and recapitulated by otheremmtypes by inactivating mutations. We hypothesised that other leading genotypes may have undergone a similar recombination events. We analysed a longitudinal dataset of genomes from 344 clinical invasive disease isolates representative of locations across England, dating from 2001 to 2011, and an international collection ofS. pyogenesgenomes representing 54 different genotypes, and found frequent evidence of recombination events at thenga-slolocus predicted to confer higher toxin expression. We identified multiple associations between recombination at this locus and inactivating mutations withinhasA/B,suggesting convergent evolutionary pathways in successful genotypes. This included common genotypesemm28 andemm87. The combination of no or low capsule, and high expression ofngaandslo,may underpin the success for many emergentS. pyogeneslineages of different genotypes, triggering new pandemics and could change the wayS. pyogenescauses disease.ImportanceStreptococcus pyogenesis a genetically diverse pathogen, with over 200 different genotypes defined byemmtyping, but only a minority of these genotypes are responsible for 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. AsS. pyogenespathogenesis 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.


mBio ◽  
2015 ◽  
Vol 6 (5) ◽  
Author(s):  
Luchang Zhu ◽  
Randall J. Olsen ◽  
Waleed Nasser ◽  
Ivan de la Riva Morales ◽  
James M. Musser

ABSTRACTStrains ofemm89Streptococcus pyogeneshave become one of the major causes of invasive infections worldwide in the last 10 years. We recently sequenced the genome of 1,125emm89strains and identified three major phylogenetic groups, designated clade 1, clade 2, and the epidemic clade 3. Epidemic clade 3 strains, which now cause the great majority of infections, have two distinct genetic features compared to clade 1 and clade 2 strains. First, all clade 3 organisms have a variant 3ngapromoter region pattern, which is associated with increased production of secreted cytolytic toxins SPN (S. pyogenesNADase) and SLO (streptolysin O). Second, all clade 3 strains lack thehasABClocus mediating hyaluronic acid capsule synthesis, whereas this locus is intact in clade 1 and clade 2 strains. We constructed isogenic mutant strains that produce different levels of SPN and SLO toxins and capsule (none, low, or high). Here we report thatemm89strains with elevated toxin production are significantly more virulent than low-toxin producers. Importantly, we also show that capsule production is dispensable for virulence in strains that already produce high levels of SPN and SLO. Our results provide new understanding about the molecular mechanisms contributing to the rapid emergence and molecular pathogenesis of epidemic clade 3emm89S. pyogenes.IMPORTANCES. pyogenes(group A streptococcus [GAS]) causes pharyngitis (“strep throat”), necrotizing fasciitis, and other human infections. Serious infections caused byemm89S. pyogenesstrains have recently increased in frequency in many countries. Based on whole-genome sequence analysis of 1,125 strains recovered from patients on two continents, we discovered that a newemm89clone, termed clade 3, has two distinct genetic features compared to its predecessors: (i) absence of the genes encoding antiphagocytic hyaluronic acid capsule virulence factor and (ii) increased production of the secreted cytolytic toxins SPN and SLO.emm89S. pyogenesstrains with the clade 3 phenotype (absence of capsule and high expression of SPN and SLO) are highly virulent in mice. These findings provide new understanding of how new virulent clones emerge and cause severe infections worldwide. This newfound knowledge ofS. pyogenesvirulence can be used to help understand future epidemics and conduct new translational research.


2015 ◽  
Vol 197 (19) ◽  
pp. 3191-3205 ◽  
Author(s):  
Yun-Juan Bao ◽  
Zhong Liang ◽  
Jeffrey A. Mayfield ◽  
Shaun W. Lee ◽  
Victoria A. Ploplis ◽  
...  

ABSTRACTThe two-componentcontrolofvirulence (Cov) regulator (R)-sensor (S) (CovRS) regulates the virulence ofStreptococcus pyogenes(group AStreptococcus[GAS]). Inactivation of CovS during infection switches the pathogenicity of GAS to a more invasive form by regulating transcription of diverse virulence genes via CovR. However, the manner in which CovRS controls virulence through expression of extended gene families has not been fully determined. In the current study, the CovS-regulated gene expression profiles of a hypervirulentemm23GAS strain (M23ND/CovS negative [M23ND/CovS−]) and a noninvasive isogenic strain (M23ND/CovS+), under different growth conditions, were investigated. RNA sequencing identified altered expression of ∼349 genes (18% of the chromosome). The data demonstrated that M23ND/CovS−achieved hypervirulence by allowing enhanced expression of genes responsible for antiphagocytosis (e.g.,hasABC), by abrogating expression of toxin genes (e.g.,speB), and by compromising gene products with dispensable functions (e.g.,sfb1). Among these genes, several (e.g.,parEandparC) were not previously reported to be regulated by CovRS. Furthermore, the study revealed that CovS also modulated the expression of a broad spectrum of metabolic genes that maximized nutrient utilization and energy metabolism during growth and dissemination, where the bacteria encounter large variations in available nutrients, thus restructuring metabolism of GAS for adaption to diverse growth environments. From constructing a genome-scale metabolic model, we identified 16 nonredundant metabolic gene modules that constitute unique nutrient sources. These genes were proposed to be essential for pathogen growth and are likely associated with GAS virulence. The genome-wide prediction of genes associated with virulence identifies new candidate genes that potentially contribute to GAS virulence.IMPORTANCEThe CovRS system modulates transcription of ∼18% of the genes in theStreptococcus pyogenesgenome. Mutations that inactivate CovR or CovS enhance the virulence of this bacterium. We determined complete transcriptomes of a naturally CovS-inactivated invasive deep tissue isolate of anemm23strain ofS. pyogenes(M23ND) and its complemented avirulent variant (CovS+). We identified diverse virulence genes whose altered expression revealed a genetic switching of a nonvirulent form of M23ND to a highly virulent strain. Furthermore, we also systematically uncovered for the first time the comparative levels of expression of a broad spectrum of metabolic genes, which reflected different metabolic needs of the bacterium as it invaded deeper tissue of the human host.


2014 ◽  
Vol 82 (12) ◽  
pp. 5293-5307 ◽  
Author(s):  
Marina Falaleeva ◽  
Oliwia W. Zurek ◽  
Robert L. Watkins ◽  
Robert W. Reed ◽  
Hadeel Ali ◽  
...  

ABSTRACTThe important human pathogenStreptococcus pyogenes(group AStreptococcus[GAS]) produces a hyaluronic acid (HA) capsule that plays critical roles in immune evasion. Previous studies showed that thehasABCoperon encoding the capsule biosynthesis enzymes is under the control of a single promoter, P1, which is negatively regulated by the two-component regulatory system CovR/S. In this work, we characterize the sequence upstream of P1 and identify a novel regulatory region controlling transcription of the capsule biosynthesis operon in the M1 serotype strain MGAS2221. This region consists of a promoter, P2, which initiates transcription of a novel small RNA, HasS, an intrinsic transcriptional terminator that inefficiently terminates HasS, permitting read-through transcription ofhasABC, and a putative promoter which lies upstream of P2. Electrophoretic mobility shift assays, quantitative reverse transcription-PCR, and transcriptional reporter data identified CovR as a negative regulator of P2. We found that the P1 and P2 promoters are completely repressed by CovR, and capsule expression is regulated by the putative promoter upstream of P2. Deletion ofhasSor of the terminator eliminates CovR-binding sequences, relieving repression and increasing read-through,hasAtranscription, and capsule production. Sequence analysis of 44 GAS genomes revealed a high level of polymorphism in the HasS sequence region. Most of the HasS variations were located in the terminator sequences, suggesting that this region is under strong selective pressure. We discovered that the terminator deletion mutant is highly resistant to neutrophil-mediated killing and is significantly more virulent in a mouse model of GAS invasive disease than the wild-type strain. Together, these results are consistent with the naturally occurring mutations in this region modulating GAS virulence.


mBio ◽  
2016 ◽  
Vol 7 (3) ◽  
Author(s):  
Vincent A. Fischetti ◽  
James B. Dale

ABSTRACT The ability to hide in the animal kingdom is essential for survival; the same is true for bacteria . Streptococcus pyogenes is considered one of the more successful stealth bacteria in its production of a hyaluronic acid capsule that is chemically identical to the hyaluronic acid lining human joints. It has also acquired the capacity to enter eukaryotic cells to avoid the onslaught of the host’s immune defenses, as well as drugs. From this intracellular vantage point, it may remain dormant from days to weeks, only to cause disease again at a later time, perhaps causing a relapse in a drug-treated patient. We now learn that it is able to enter macrophages as well, enabling the Streptococcus to use this “Trojan horse” approach to be transported to distant sites in the body.


mBio ◽  
2020 ◽  
Vol 11 (4) ◽  
Author(s):  
Yi-Hsuan Chen ◽  
Shao-Hui Li ◽  
Yao-Cheng Yang ◽  
Shu-Hao Hsu ◽  
Victor Nizet ◽  
...  

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.


2017 ◽  
Vol 83 (12) ◽  
Author(s):  
Jingqiu Liao ◽  
Martin Wiedmann ◽  
Jasna Kovac

ABSTRACT Sequencing of single genes remains an important tool that allows the rapid classification of bacteria. Sequencing of a portion of sigB, which encodes a stress-responsive alternative sigma factor, has emerged as a commonly used molecular tool for the initial characterization of diverse Listeria isolates. In this study, evolutionary approaches were used to assess the validity of sigB allelic typing for Listeria. For a data set of 4,280 isolates, sigB allelic typing showed a Simpson's index of diversity of 0.96. Analyses of 164 sigB allelic types (ATs) found among the 6 Listeria sensu stricto species, representing these 4,280 isolates, indicate that neither frequent homologous recombination nor positive selection significantly contributed to the evolution of sigB, confirming its genetic stability. The molecular clock test provided evidence for unequal evolution rates across clades; Listeria welshimeri displayed the lowest sigB diversity and was the only species in which sigB evolved in a clocklike manner, implying a unique natural history. Among the four L. monocytogenes lineages, sigB evolution followed a molecular clock only in lineage IV. Moreover, sigB displayed a significant negative Tajima D value in lineage II, suggesting a recent population bottleneck followed by lineage expansion. The absence of positive selection along with the violation of the molecular clock suggested a nearly neutral mechanism of Listeria sensu stricto sigB evolution. While comparison with a whole-genome sequence-based phylogeny revealed that the sigB phylogeny did not correctly reflect the ancestry of L. monocytogenes lineage IV, the availability of a large sigB AT database allowed accurate species classification. IMPORTANCE sigB allelic typing has been widely used for species delineation and subtyping of Listeria. However, an informative evaluation of this method from an evolutionary perspective was missing. Our data indicate that the genetic stability of sigB is affected by neither frequent homologous recombination nor positive selection, which supports that sigB allelic typing provides reliable subtyping and classification of Listeria sensu stricto strains. However, multigene data are required for accurate phylogeny reconstruction of Listeria. This study thus contributes to a better understanding of the evolution of sigB and confirms the robustness of the sigB subtyping system for Listeria.


2013 ◽  
Vol 79 (21) ◽  
pp. 6803-6812 ◽  
Author(s):  
Ave Tooming-Klunderud ◽  
Hanne Sogge ◽  
Trine Ballestad Rounge ◽  
Alexander J. Nederbragt ◽  
Karin Lagesen ◽  
...  

ABSTRACTHorizontal gene transfer is common in cyanobacteria, and transfer of large gene clusters may lead to acquisition of new functions and conceivably niche adaption. In the present study, we demonstrate that horizontal gene transfer between closely relatedPlanktothrixstrains can explain the production of the same oligopeptide isoforms by strains of different colors. Comparison of the genomes of eightPlanktothrixstrains revealed that strains producing the same oligopeptide isoforms are closely related, regardless of color. We have investigated genes involved in the synthesis of the photosynthetic pigments phycocyanin and phycoerythrin, which are responsible for green and red appearance, respectively. Sequence comparisons suggest the transfer of a functional phycoerythrin gene cluster generating a red phenotype in a strain that is otherwise more closely related to green strains. Our data show that the insertion of a DNA fragment containing the 19.7-kb phycoerythrin gene cluster has been facilitated by homologous recombination, also replacing a region of the phycocyanin operon. These findings demonstrate that large DNA fragments spanning entire functional gene clusters can be effectively transferred between closely related cyanobacterial strains and result in a changed phenotype. Further, the results shed new light on the discussion of the role of horizontal gene transfer in the sporadic distribution of large gene clusters in cyanobacteria, as well as the appearance of red and green strains.


2016 ◽  
Vol 84 (5) ◽  
pp. 1361-1370 ◽  
Author(s):  
Marianne Mégroz ◽  
Oded Kleifeld ◽  
Amy Wright ◽  
David Powell ◽  
Paul Harrison ◽  
...  

The Gram-negative bacteriumPasteurella multocidais the causative agent of a number of economically important animal diseases, including avian fowl cholera. NumerousP. multocidavirulence factors have been identified, including capsule, lipopolysaccharide (LPS), and filamentous hemagglutinin, but little is known about how the expression of these virulence factors is regulated. Hfq is an RNA-binding protein that facilitates riboregulation via interaction with small noncoding RNA (sRNA) molecules and their mRNA targets. Here, we show that aP. multocidahfqmutant produces significantly less hyaluronic acid capsule during all growth phases and displays reducedin vivofitness. Transcriptional and proteomic analyses of thehfqmutant during mid-exponential-phase growth revealed altered transcript levels for 128 genes and altered protein levels for 78 proteins. Further proteomic analyses of thehfqmutant during the early exponential growth phase identified 106 proteins that were produced at altered levels. Both the transcript and protein levels for genes/proteins involved in capsule biosynthesis were reduced in thehfqmutant, as were the levels of the filamentous hemagglutinin protein PfhB2 and its secretion partner LspB2. In contrast, there were increased expression levels of three LPS biosynthesis genes, encoding proteins involved in phosphocholine and phosphoethanolamine addition to LPS, suggesting that these genes are negatively regulated by Hfq-dependent mechanisms. Taken together, these data provide the first evidence that Hfq plays a crucial role in regulating the global expression ofP. multocidagenes, including the regulation of keyP. multocidavirulence factors, capsule, LPS, and filamentous hemagglutinin.


2020 ◽  
Vol 47 (3) ◽  
pp. 547-560 ◽  
Author(s):  
Darush Yazdanfar ◽  
Peter Öhman

PurposeThe purpose of this study is to empirically investigate determinants of financial distress among small and medium-sized enterprises (SMEs) during the global financial crisis and post-crisis periods.Design/methodology/approachSeveral statistical methods, including multiple binary logistic regression, were used to analyse a longitudinal cross-sectional panel data set of 3,865 Swedish SMEs operating in five industries over the 2008–2015 period.FindingsThe results suggest that financial distress is influenced by macroeconomic conditions (i.e. the global financial crisis) and, in particular, by various firm-specific characteristics (i.e. performance, financial leverage and financial distress in previous year). However, firm size and industry affiliation have no significant relationship with financial distress.Research limitationsDue to data availability, this study is limited to a sample of Swedish SMEs in five industries covering eight years. Further research could examine the generalizability of these findings by investigating other firms operating in other industries and other countries.Originality/valueThis study is the first to examine determinants of financial distress among SMEs operating in Sweden using data from a large-scale longitudinal cross-sectional database.


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