Streptococci Overview and Characteristics
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Questions and Answers

What characteristic distinguishes beta-hemolytic streptococci?

  • Alpha hemolysis with green discoloration
  • Partial hemolysis of red blood cells
  • No hemolysis of red blood cells
  • Complete hemolysis of red blood cells (correct)

    • Which species is most commonly associated with the pyogenic group of streptococci?

  • Streptococcus pyogenes (correct)
  • Streptococcus agalactiae
  • Enterococcus faecalis
  • Streptococcus pneumoniae

    • Which of the following statements about viridans group streptococci is true?

  • They are part of the Lancefield classification
  • They are primarily beta-hemolytic
  • They are alpha-hemolytic or non-hemolytic (correct)
  • They do not grow at 45°C

    • What is a defining feature of lactic group streptococci?

    <p>They grow at lower temperatures, specifically at 10°C</p> Signup and view all the answers

    Which characteristic is NOT typical of streptococci?

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

    What is the significance of the C carbohydrate layer in streptococci?

    <p>It is used for serological classification</p> Signup and view all the answers

    Which of the following media components enhances the growth of streptococci on an agar plate?

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

    Which characteristic is true for gamma-hemolytic streptococci?

    <p>They exhibit no lysis of red blood cells</p> Signup and view all the answers

    What characteristic differentiates Group A streptococci from other groups?

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

    Which enzyme produced by S.pyogenes is responsible for lysis of white blood cells?

    <p>Streptolysin S</p> Signup and view all the answers

    What is the main pathogenic modality for the transmission of Group A streptococci?

    <p>Contaminated droplets from cough or sneeze</p> Signup and view all the answers

    Which of the following groups of Streptococci does not have a Lancefield classification?

    <p>α (alpha) hemolytic</p> Signup and view all the answers

    What is the significance of the ASO test?

    <p>It identifies the presence of streptolysin O</p> Signup and view all the answers

    What role does hyaluronidase play in the pathogenicity of S.pyogenes?

    <p>It aids in tissue separation and bacterial spreading</p> Signup and view all the answers

    Which of the following species is classified under Group B streptococci?

    <p>S.agalactiae</p> Signup and view all the answers

    What is the primary action of streptokinase produced by S.pyogenes?

    <p>To activate plasminogen and dissolve fibrin clots</p> Signup and view all the answers

    Which of the following symptoms is NOT typically associated with Scarlet Fever?

    <p>Severe abdominal pain</p> Signup and view all the answers

    What is the function of exotoxin B produced by S.pyogenes?

    <p>Degrades proteins</p> Signup and view all the answers

    What is the primary method of transmission for Scarlet Fever?

    <p>Respiratory droplets</p> Signup and view all the answers

    Which test is used to assess susceptibility to erythrogenic toxin in Scarlet Fever?

    <p>Schultz Charlton reaction</p> Signup and view all the answers

    Which condition is characterized by a defined area of redness and fluid accumulation?

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

    What is a potential severe complication of erysipelas?

    <p>Necrotizing fasciitis</p> Signup and view all the answers

    Which test differentiates S.pyogenes from other beta-hemolytic groups?

    <p>Bacitracin disk test</p> Signup and view all the answers

    What characterizes acute glomerulonephritis?

    <p>Inflammation of the renal glomeruli</p> Signup and view all the answers

    What is the growth requirement for E.faecalis?

    <p>Requires cyanocobalamin (B12) as a growth factor</p> Signup and view all the answers

    Which test result is typical for Group B streptococci?

    <p>Negative in bile esculin test</p> Signup and view all the answers

    Which species is known to cause dental caries?

    <p>S.mutans</p> Signup and view all the answers

    Which characteristic is NOT associated with viridans streptococci?

    <p>Bile soluble</p> Signup and view all the answers

    What is a necessary condition for the growth of Abiotrophia on blood agar plates (BAP)?

    <p>Supplementation with pyridoxal (B6)</p> Signup and view all the answers

    Which test is used to visually enhance the beta hemolysis of Group A streptococci on BAP?

    <p>Inoculating by stabbing the agar</p> Signup and view all the answers

    What is the primary mode of satellite growth observed with Abiotrophia?

    <p>Around organisms that produce pyridoxal</p> Signup and view all the answers

    What infection is commonly associated with viridans streptococci?

    <p>Subacute endocarditis</p> Signup and view all the answers

    What is the principal virulence factor of Streptococcus pneumoniae?

    <p>Antiphagocytic capsular polysaccharide</p> Signup and view all the answers

    Which of the following tests can differentiate Streptococcus pneumoniae from viridans streptococci?

    <p>Bile solubility test</p> Signup and view all the answers

    What type of infections is commonly caused by Streptococcus pneumoniae?

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

    Which test uses bacitracin disks for susceptibility testing?

    <p>Bacitracin disk test</p> Signup and view all the answers

    Which colony appearance is characteristic of old colonies of Streptococcus pneumoniae?

    <p>Dome-shaped with a raised rim</p> Signup and view all the answers

    What kind of bacteria is Streptococcus pneumoniae classified as?

    <p>Gram-positive cocci in pairs</p> Signup and view all the answers

    What is a notable enzyme produced by Streptococcus pneumoniae?

    <p>Immunoglobulin A protease</p> Signup and view all the answers

    What percentage of the normal flora of the upper respiratory tract do Streptococcus pneumoniae represent in preschool children?

    <p>25-50%</p> Signup and view all the answers

    Study Notes

    Gram-Positive Cocci: Streptococci Overview

    • Gram-positive spherical cells arranged in chains or pairs.
    • Colonies appear grayish, translucent to slightly opaque; pinpoint in size.
    • Catalase negative and oxidase negative.
    • Growth is enhanced by blood, serum, or glucose in agar plates.

    Growth Characteristics

    • Behave as facultative anaerobes; some species require increased CO2.
    • Aerotolerant anaerobes; Peptostreptococci are obligate anaerobes.
    • Young cultures exhibit a capsule, and they are common in normal human flora.

    Serological Classification

    • All streptococci except viridans group have C carbohydrate for serological classification.
    • When they access sterile sites, they can cause serious infections, notably S. pyogenes and S. pneumoniae.

    Colony Variation

    • Variants include mucoid, matte or rough (high CHON), and smooth/glossy (low CHON).

    Classification Based on Temperature

    • Pyogenic Group: β-hemolytic, does not grow at 10°C or 45°C (e.g., S. pyogenes).
    • Viridans Group: Grows at 45°C, not part of Lancefield group, alpha or non-hemolytic (e.g., S. salivarius).
    • Enterococcus: Grows at both 10°C and 45°C; normal flora of the intestine (e.g., E. faecalis).
    • Lactic Group: Grows at 10°C and is non-hemolytic; often found in dairy (e.g., S. lactis).

    Classification Based on Hemolytic Patterns

    • Alpha-Hemolytic: Partial hemolysis; green discoloration (e.g., S. pneumoniae).
    • Beta-Hemolytic: Complete hemolysis; clear zone (e.g., S. pyogenes, S. agalactiae).
    • Gamma-Hemolytic: No lysis; unchanged surrounding red cells (e.g., E. faecalis).

    Lancefield Classification

    • Based on antigenic nature of cell wall carbohydrates (C polysaccharides).
    • Group classifications include:
      • α: None - S. pneumoniae
      • β: A - S. pyogenes, B - S. agalactiae
      • γ: D - Enterococcus spp.

    Group A Streptococci

    • Pathogenic; not part of normal flora; transmitted via respiratory droplets (e.g., S. pyogenes).
    • M-protein serves as a principal virulence factor and is anti-phagocytic.
    • Other factors include:
      • Protein F for cell attachment.
      • Lipoteichoic acid for adherence to respiratory epithelium.

    Enzymes and Toxins of S. pyogenes

    • Streptolysin O: Oxygen-labile, antigenic; responsible for subsurface hemolysis; lysis of WBCs.
    • Streptolysin S: Oxygen-stable; surface hemolysis.
    • Deoxyribonucleases: Hydrolyzes DNA.
    • Streptokinase: Activates plasminogen for movement from clotted areas.
    • Hyaluronidase: Spreads the organism by separating tissue.
    • Pyrogenic toxins: Serotypes A, B, C; cause rashes and other symptoms.

    Infections Associated with S. pyogenes

    • Pharyngitis/Tonsillitis: Known as "strep throat."
    • Scarlet Fever: Resulting from an S. pyogenes throat infection with erythrogenic toxin; features a characteristic rash and "strawberry tongue."
    • Skin Infections: Includes cellulitis and erysipelas, with potential progression to necrotizing fasciitis and myositis.
    • Rheumatic Fever and Acute Glomerulonephritis: Both are serious complications.

    Diagnostic Tests

    • Bacitracin Disk Test: Differentiates S. pyogenes, with positive results showing any zone of inhibition.
    • Sulfamethoxazole-Trimethoprim Test (SXT): Positive with zones of inhibition.
    • PYR Test: Specific for Group A; positive results yield a cherry-red color.

    Group B Streptococci

    • Normal flora of the female genital tract; can be opportunistic.
    • Notable species include E. faecalis and S. agalactiae.

    Viridans Streptococci

    • Alpha-hemolytic, lack Lancefield antigen, opportunistic pathogens.
    • Associated infections include subacute endocarditis and dental carries, particularly with S. mutans.

    Abiotrophia

    • Pyridoxal-dependent organisms; known as nutritionally variant streptococci.
    • Associated with a low virulence but can cause endocarditis.

    Streptococcus pneumoniae

    • Diplococci; major cause of bacterial pneumonia and meningitis globally.
    • Key virulence factor is the antiphagocytic capsular polysaccharide.
    • Characteristic colonies range from mucoid young colonies to hard, dimpled older colonies.

    Other Infections Caused by S. pneumoniae

    • Includes pneumonia, meningitis, otitis media, bacteremia, endocarditis, and peritonitis.

    Differential Tests for S. pneumoniae

    • Optochin Susceptibility Test: Differentiates pneumococcus from viridans streptococci.
    • Bile Solubility Test: Confirms pneumococcus by showing broth clearing after incubation.

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    Description

    This quiz covers the essential characteristics of Gram-positive cocci, focusing on streptococci. It includes details on their growth, serological classification, colony variation, and responses to temperature. Test your knowledge of these important bacteria and their significance in human health.

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