Streptococcus 1

• What type of bacteria is Streptococcus?

  Gram positive bacteria
• How are streptococci arranged?

  They are arranged in pairs or chains
• Are streptococci motile or non-motile?

  Non-motile
• What type of respiration do streptococci perform?

  They are aerobes and facultative anaerobes
• What is the catalase test result for streptococci?

  Catalase-negative
• What methods are used for the classification of streptococci?

  • Colony morphology
  • Hemolytic reactions on blood agar
  • Serologic specificity of group-specific antigens
  • other methods:
  • Biochemical reactions
  • Molecular genetics
• What type of hemolysis do beta-hemolytic streptococci exhibit?

  Complete hemolysis
• Which streptococci are classified as beta-hemolytic?

  Streptococcus pyogenes and Streptococcus agalactiae
• What is the hemolytic reaction of alpha-hemolytic streptococci?

  Partial hemolysis
• What color zone do alpha-hemolytic streptococci form on blood agar?

  A green zone
• What causes the green color around alpha-hemolytic streptococci colonies?

  Oxidation of hemoglobin to biliverdin by hydrogen peroxide
• What is the hemolytic reaction of gamma-hemolytic streptococci?

  No hemolysis
• What is the Lancefield grouping based on?

  • Possession of group-specific C-Carbohydrates antigen on the streptococcal cell wall
  • Using agglutination reactions or immunofluorescence
  • Groups A-H and K-U
• Which group does Streptococcus pyogenes belong to?

  Group A
• Which group does Streptococcus agalactiae belong to?

  Group B
• Which group do Enterococci belong to?

  Group D
• Which streptococci cannot be typed by Lancefield grouping?

  Streptococcus pneumoniae and viridans streptococci
• What are the medically important streptococci?


  • Streptococcus pyogenes (Group A)
  • Streptococcus agalactiae (Group B)
  • Streptococcus pneumoniae (pneumococci)
  • Viridans streptococci
  • Enterococci (Group D)
• What is the virulence of Streptococcus pyogenes?

  Most virulent species
• What type of infections does Streptococcus pyogenes cause?


  Systemic illnesses
• What is the normal habitat of Streptococcus pyogenes?

  Inhabitant in mouth, skin, and nasopharynx
• What are the structural components of Streptococcus pyogenes?

  • Capsule: Hyaluronic acid (non-immunogenic)
  • Fimbriae: M protein + Lipoteichoic acid (adhesion)
  • C-carbohydrates antigen: group specific marker
  • F protein: fibronectin binding (attachment to epithelial cells)
• What are the virulence factors of Streptococcus pyogenes?

  • M protein: Resists phagocytosis, antigenic
  • Extracellular enzymes: Hyaluronidase, DNAse, Streptokinase, C5a peptidase
  • Exotoxins: Streptolysins (O and S), Pyrogenic Exotoxins (A-C), Erythrogenic toxin
• What is the role of M protein in Streptococcus pyogenes?

  It resists phagocytosis and is antigenic
• What is the function of hyaluronidase produced by Streptococcus pyogenes?

  It degrades hyaluronic acid and acts as a spreading factor
• What is the function of DNAse produced by Streptococcus pyogenes?

  It degrades DNA in necrotic tissue and acts as a spreading factor
• What is the role of streptokinase in Streptococcus pyogenes?

  It converts plasminogen to plasmin and is used therapeutically for treatment of myocardial infarction
• What is the function of C5a peptidase produced by Streptococcus pyogenes?

  It degrades complement fragment C5a and prevents chemotaxis of phagocytes
• What are the two types of streptolysins produced by Streptococcus pyogenes?

  Streptolysin O (oxygen labile) and Streptolysin S (oxygen stable)
• What is the significance of Streptolysin O in diagnosis?

  It is antigenic and can be diagnosed by antistreptolysin O (ASO) test
• What are pyrogenic exotoxins produced by Streptococcus pyogenes?

  Exotoxins A-C, which are superantigens and can result in toxic shock syndrome
• What is the role of erythrogenic toxin in Streptococcus pyogenes?

  It is a superantigen that causes scarlet fever
• What types of infections are caused by Streptococcus pyogenes?

  • Pyogenic infections
  • Toxigenic infections
  • Immune-mediated (post-infections)
• What are examples of pyogenic infections caused by Streptococcus pyogenes?


  • Strep throat
  • Cellulitis
  • Erysipelas
  • Impetigo
  • Puerperal sepsis
• What are the symptoms of strep throat caused by Streptococcus pyogenes?

  Sore throat, fever, and cervical lymph nodes enlargement
• What are the complications of strep throat?

  Paratonsillar abscess and retropharyngeal abscess
• What is cellulitis and its association with Streptococcus pyogenes?

  Acute infection of the skin and subcutaneous tissues associated with trauma, burns, or surgical incisions
• What are the symptoms of erysipelas caused by Streptococcus pyogenes?

  Pain, fever, and lymphadenopathy
• What is puerperal sepsis and its association with Streptococcus pyogenes?

  Infection of the endometrium following labor, leading to systemic illness
• What is impetigo and its association with Streptococcus pyogenes?

  A superficial skin infection usually affecting children, characterized by vesicles filled with pus