title: Trading Capsule for Increased Cytotoxin Production: Contribution to Virulence of a Newly Emerged Clade of emm89 Streptococcus pyogenes.
abstract: Strains of emm89 Streptococcus pyogenes have become one of the major causes of invasive infections worldwide in the last 10 years. We recently sequenced the genome of 1,125 emm89 strains 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 3 nga promoter region pattern, which is associated with increased production of secreted cytolytic toxins SPN (S. pyogenes NADase) and SLO (streptolysin O). Second, all clade 3 strains lack the hasABC locus 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 that emm89 strains 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 3 emm89 S. pyogenes.
  
  
  OBJECTIVE
  S. pyogenes (group A streptococcus [GAS]) causes pharyngitis ("strep throat"), necrotizing fasciitis, and other human infections. Serious infections caused by emm89 S. pyogenes strains 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 new emm89 clone, 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. emm89 S. pyogenes strains 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 of S. pyogenes virulence can be used to help understand future epidemics and conduct new translational research.
authors.affiliation: Center for Molecular and Translational Human Infectious Diseases Research, Houston Methodist Research Institute, Houston, Texas, USA Department of Pathology and Genomic Medicine, Houston Methodist Hospital, Houston, Texas, USA.
authors.forename: Luchang
authors.initials: L
authors.lastname: Zhu
authors.affiliation: Center for Molecular and Translational Human Infectious Diseases Research, Houston Methodist Research Institute, Houston, Texas, USA Department of Pathology and Genomic Medicine, Houston Methodist Hospital, Houston, Texas, USA.
authors.forename: Randall J
authors.initials: RJ
authors.lastname: Olsen
authors.affiliation: Center for Molecular and Translational Human Infectious Diseases Research, Houston Methodist Research Institute, Houston, Texas, USA Department of Pathology and Genomic Medicine, Houston Methodist Hospital, Houston, Texas, USA.
authors.forename: Waleed
authors.initials: W
authors.lastname: Nasser
authors.affiliation: Center for Molecular and Translational Human Infectious Diseases Research, Houston Methodist Research Institute, Houston, Texas, USA Department of Pathology and Genomic Medicine, Houston Methodist Hospital, Houston, Texas, USA Escuela de Medicina y Ciencias de la Salud, Instituto Tecnológico y de Estudios Superiores de Monterrey, Monterrey, Nuevo León, México.
authors.forename: Ivan
authors.initials: I
authors.lastname: de la Riva Morales
authors.affiliation: Center for Molecular and Translational Human Infectious Diseases Research, Houston Methodist Research Institute, Houston, Texas, USA Department of Pathology and Genomic Medicine, Houston Methodist Hospital, Houston, Texas, USA jmmusser@houstonmethodist.org.
authors.forename: James M
authors.initials: JM
authors.lastname: Musser
mesh_terms: D000818:Animals; D016667:Bacterial Capsules / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism; D053898:Biosynthetic Pathways / Q000235:genetics*; D004195:Disease Models, Animal; D019115:Fasciitis, Necrotizing / Q000382:microbiology / Q000473:pathology; D006651:Histocytochemistry; D006801:Humans; D006820:Hyaluronic Acid / Q000096:biosynthesis*; D051379:Mice; D008853:Microscopy; D009244:NAD+ Nucleosidase / Q000378:metabolism*; D013290:Streptococcal Infections / Q000382:microbiology / Q000473:pathology; D013297:Streptococcus pyogenes / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D013301:Streptolysins / Q000378:metabolism*; D016019:Survival Analysis; D014774:Virulence; D037521:Virulence Factors / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D013301:Streptolysins; D037521:Virulence Factors; C025964:streptolysin O; D006820:Hyaluronic Acid; D009244:NAD+ Nucleosidase