Characteristics and Classification of Streptococci
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Questions and Answers

What is the characteristic arrangement of gram-positive cocci in Streptococci?

  • In clusters
  • In pairs or chains (correct)
  • In single cells
  • In irregular patterns

    • What is the primary basis for serologic grouping of streptococci?

  • Fatty acid composition
  • Nucleic acid sequence
  • Protein structure
  • Carbohydrate (correct)

    • What is the function of M protein in Streptococci?

  • Increases virulence
  • Decreases acid resistance
  • Inhibits phagocytosis (correct)
  • Enhances phagocytosis

    • Which of the following is NOT a characteristic of Streptococci?

    <p>Catalase-positive</p> Signup and view all the answers

    What is the name of the disease caused by Streptococcus pyogenes?

    <p>All of the above</p> Signup and view all the answers

    What is the effect of 10% carbon dioxide on the growth of Streptococci?

    <p>Enhances growth</p> Signup and view all the answers

    What is the type of hemolysis caused by Streptococcus pyogenes?

    <p>β -hemolysis</p> Signup and view all the answers

    What is the name of the component of Streptococci that provides type-specific immunity?

    <p>M protein</p> Signup and view all the answers

    What is the primary function of the polysaccharide capsule in Streptococcus pyogenes?

    <p>To retard phagocytosis</p> Signup and view all the answers

    What is the main difference between group A streptococci and group B streptococci in response to the bacitracin test?

    <p>Group A streptococci produce a wider zone of inhibition</p> Signup and view all the answers

    Which of the following enzymes is NOT produced by Streptococcus pyogenes?

    <p>Lipase</p> Signup and view all the answers

    What is the primary site of colonization for Streptococcus agalactiae?

    <p>Vagina and colon</p> Signup and view all the answers

    What is the mechanism by which Streptococcus pyogenes adheres to pharyngeal epithelium?

    <p>Via M protein and lipoteichoic acid</p> Signup and view all the answers

    What is the result of the growth of Streptococcus pyogenes on agar plates in the laboratory when exposed to bacitracin?

    <p>Zone of inhibition</p> Signup and view all the answers

    How do group A streptococci cause disease?

    <p>Through pyogenic inflammation, exotoxin production, and immunologic response</p> Signup and view all the answers

    What is the role of M protein in group A streptococci?

    <p>To confer rheumatogenicity</p> Signup and view all the answers

    What is the main predisposing factor for neonatal sepsis, pneumonia, and meningitis caused by Group B streptococci?

    <p>Prolonged rupture of the membranes in women who lack antibody to Group B streptococci IgGs</p> Signup and view all the answers

    What is a characteristic of Group B streptococci?

    <p>They hydrolyze hippurate</p> Signup and view all the answers

    What is a complication of Group B streptococcal infections in adults?

    <p>Endocarditis</p> Signup and view all the answers

    What is the primary site of colonization for Group B streptococci?

    <p>Genital tract</p> Signup and view all the answers

    What is a major criterion in the diagnosis of rheumatic fever?

    <p>Erythema marginatum</p> Signup and view all the answers

    What is the main predisposing factor for adult Group B streptococcal infections?

    <p>Diabetes</p> Signup and view all the answers

    What is the function of hyaluronidase in Skin infections?

    <p>It degrades hyaluronic acid and facilitates the rapid spread of Str.pyogenes</p> Signup and view all the answers

    What is the mechanism of action of erythrogenic toxin?

    <p>It acts as a superantigen, similar to TSST of Sta.aureus</p> Signup and view all the answers

    What is the function of streptolysin O?

    <p>It is a hemolysin that causes β-hemolysis when colonies grow under the surface of a blood agar plate</p> Signup and view all the answers

    What is the function of streptolysin S?

    <p>It causes β-hemolysis when colonies grow on the surface of a blood agar plate</p> Signup and view all the answers

    What is the function of pyogenic exotoxin A?

    <p>It is a superantigen that causes the release of large amounts of cytokines from helper T cells and macrophages</p> Signup and view all the answers

    What is the function of exotoxin B?

    <p>It is a protease that rapidly destroys tissue</p> Signup and view all the answers

    What is the significance of the Dick test?

    <p>It is a skin test used to determine if a person has antitoxin against erythrogenic toxin</p> Signup and view all the answers

    What is the significance of the titer of ASO antibody?

    <p>It is important in the diagnosis of rheumatic fever</p> Signup and view all the answers

    Study Notes

    Characteristics of Streptococci

    • Spherical or oval gram-positive cocci arranged in chains or pairs
    • Facultative anaerobes
    • Grow well on ordinary solid media enriched with blood, serum, or glucose as discoid colonies
    • Capsular streptococcal strains give rise to mucoid colonies
    • Aerobic bacteria in which growth is enhanced with 10% carbon dioxide
    • Catalase-negative
    • Heterogeneous group of bacteria

    Classification of Streptococci

    • Based on:
      • Colony morphology and hemolysis in blood agar
      • Serologic specificity of the cell wall group-specific substances or capsular antigens
      • Biochemical reactions and resistance to physical and chemical factors
      • Molecular genetics

    α and β-Hemolysis

    • α-Hemolysis: partial lysis of red blood cells
    • β-Hemolysis: complete lysis of red blood cells
    • α-Hemolytic colony: probably a viridans group streptococcus
    • β-Hemolytic colony: probably Streptococcus pyogenes

    Diseases Caused by Streptococcus pyogenes

    • Pharyngitis
    • Cellulitis
    • Impetigo
    • Necrotizing fasciitis
    • Streptococcal toxic shock syndrome
    • Rheumatic fever
    • Acute glomerulonephritis

    Antigenic Structure of Streptococcus pyogenes

    • Group-specific cell wall antigen (carbohydrate)
    • M protein (most important virulence factor)
      • Found in hair-like projections on the outer surface of the streptococcal cell
      • Antiphagocytic
      • Acid and heat resistant
      • Provides type-specific immunity
    • Polysaccharide capsule (plays a role in retarding phagocytosis)
    • Protein F (fibronectin-binding proteins)

    Transmission of Streptococcus pyogenes

    • Part of the normal flora of the human throat, skin, and intestines
    • Produce disease when they gain access to tissues or blood
    • Found on the skin and in the oropharynx in small numbers

    Streptococcus pyogenes - Pathogenesis

    • Cause disease by three mechanisms:
      • Pyogenic inflammation
      • Exotoxin production
      • Immunologic
    • Produce three important inflammation-related enzymes:
      • Hyaluronidase (degrades hyaluronic acid, facilitates rapid spread of Str.pyogenes in skin infections)
      • Streptokinase (activates plasminogen to form plasmin, which dissolves fibrin in clots, thrombi, and emboli)
    • Produce five important toxins and hemolysins:
      • Erythrogenic toxin (causes the rash of scarlet fever, acts as a superantigen)
      • Streptolysin O (hemolysin, inactivated by oxidation, causes β-hemolysis only when colonies grow under the surface of a blood agar plate)
      • Streptolysin S (hemolysin, not inactivated by oxygen, responsible for β-hemolysis when colonies grow on the surface of a blood agar plate)
      • Pyogenic exotoxin A (toxin responsible for most cases of streptococcal toxic shock syndrome, acts as a superantigen)
      • Exotoxin B (protease, rapidly destroys tissue, produced in large amounts by "flesh-eating" streptococci that cause necrotizing fasciitis)

    Group B Streptococci (Streptococcus agalactiae)

    • Colonize the genital tract of some women
    • Bacitracin-resistant
    • Hydrolyze hippurate
    • Clinical features:
      • Neonatal sepsis, pneumonia, and meningitis
      • Predisposing factor: prolonged rupture of the membranes in women who are colonized with the organism and lack antibody to group B streptococci IgGs
      • Meningitis during the first month of life
      • Pneumonia, endocarditis, arthritis, and osteomyelitis in adults
      • Postpartum endometritis
      • Diabetes is the main predisposing factor for adult group B streptococcal infections

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    Description

    Learn about the properties and classification of Streptococci, including their arrangement, metabolism, growth conditions, and differentiation based on colony morphology and hemolysis.

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