Strep pyogenes: Overview

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Streptococcus pyogenes overview 

  • Part of Group A streptococci (GAS)
  • Characteristics
    • Gram + cocci in chains
    • Catalase -
      • First step in gram positive cocci; determines staph (catalase positive) vs. strep 
    • Beta-hemolytic
      • Second step, narrows type of strep
    • Pyrrolidonyl arylamidase (PYR) +
      • Because the bacitracin test is not very specific for S pyogenes, it has been replaced in many laboratories by the pyrrolidonyl arylamidase (PYR) test
    • Bacitracin sensitive
      • Has been widely replaced with the PYR test
  • Virulence Factors
    • Hyaluronic acid capsule
    • Protein M
      • Main virulence factor for strep. pyogenes
      • Inhibits phagocytosis and activation of complement
      • Also cytotoxic to neutrophils and mediator of bacterial attachment
    • Streptolysin (Hemolysin) O
      • Lyses RBCs (causing beta-hemolysis) and polymorphonuclear leukocytes.
      • Anti-streptolysin O (ASO) titers used as marker of recent infection
    • Pyrogenic exotoxin
      • Pyrogenic = causes fever; cause of Scarlet fever
      • Superantigen that results in tissue injury and septic shock; e.g. Toxic shock syndrome
    • Streptokinase
      • Fibrinolytic (clot-buster) that is now used as a medication
      • Enables more spread from initial site of infection
    • DNAse
      • DNase is an extracellular enzyme that depolymerizes viscous DNA in pus and disintegrates polymorphonuclear leukocytes, allowing the streptococcus to move more freely in the tissue.
      • Anti-DNAse is also a titer measured as a marker of recent infection