Identifying Cocci and Hemolytic Patterns
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Questions and Answers

What was observed in the presence of hydrochloric acid regarding depolymerized DNA?

  • A zone of clearing around the colonies (correct)
  • No observable change
  • Formation of a cloudy precipitate
  • Thicker, polymerized DNA structure

    • What type of bacteria was identified from the throat culture?

  • Gram-positive cocci in clusters
  • Gram-negative cocci in pairs
  • Gram-positive cocci in long chains (correct)
  • Gram-positive bacilli

    • What kind of agar is used to indicate the hydrolysis of DNA?

  • Blood agar
  • Nutrient agar
  • Modified DNAse agar (correct)
  • Methylene blue agar

    • Which characteristic best describes the organism examined in the culture?

    <p>Catalase negative and β-hemolytic</p> Signup and view all the answers

    Which observation supports the presence of polymerized DNA in the culture?

    <p>Formation of a cloudy precipitate</p> Signup and view all the answers

    Which species is classified under Lancefield Group A?

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

    What type of hemolysis is associated with S.agalactiae?

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

    What infections are commonly associated with S.pyogenes?

    <p>Pharyngitis and cellulitis</p> Signup and view all the answers

    Which species is usually associated with γ-hemolysis?

    <p>E.faecium</p> Signup and view all the answers

    What type of infections are commonly caused by S.bovis?

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

    What is a characteristic feature of the viridans group streptococci?

    <p>They exhibit variable or non-groupable characteristics</p> Signup and view all the answers

    Which species does NOT belong to the Lancefield classification?

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

    What type of agar may have methyl green as an indicator?

    <p>Original DNA agar</p> Signup and view all the answers

    Which hemolytic pattern indicates complete lysis of RBCs?

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

    What does growth in a 6.5% sodium chloride solution indicate?

    <p>Isolate is likely enterococci</p> Signup and view all the answers

    What is the appearance of α-hemolytic streptococci on blood agar?

    <p>Greenish discoloration of the agar</p> Signup and view all the answers

    If an isolate shows no growth in a 6.5% sodium chloride solution, what is it likely to be?

    <p>Isolate is likely Streptococcus bovis</p> Signup and view all the answers

    What procedure is used to test for β-hemolytic streptococci?

    <p>Bacitracin testing</p> Signup and view all the answers

    What type of hemolysis does not lyse RBCs?

    <p>γ-hemolytic</p> Signup and view all the answers

    Which type of streptococci is resistant to optochin?

    <p>Viridans streptococci</p> Signup and view all the answers

    How is non-hemolytic characterized in terms of RBC lysis?

    <p>No lysis of RBCs</p> Signup and view all the answers

    What is the main virulence factor of Streptococcus pyrogenes?

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

    Which enzyme acts as a plasminogen activator in Streptococcus pyrogenes?

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

    What role does hyaluronidase play for Streptococcus pyrogenes?

    <p>It allows dissemination through tissue.</p> Signup and view all the answers

    What is the function of pyrogenic exotoxin in Streptococcus pyrogenes?

    <p>It acts as a superantigen.</p> Signup and view all the answers

    What is the difference between Streptolysin O and Streptolysin S?

    <p>Streptolysin S is oxygen stable.</p> Signup and view all the answers

    What complication can arise from mimicry between streptococcal M protein and cardiac myosin?

    <p>Rheumatic heart disease</p> Signup and view all the answers

    Which factor reduces the host immune response in Streptococcus pyrogenes?

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

    What symptoms did the patient experience after being diagnosed with strep throat?

    <p>Unusually dark reddish-brown urine and periorbital edema</p> Signup and view all the answers

    What does a positive reaction in the Antistreptolysin O test indicate?

    <p>Presence of streptolysin O antibodies</p> Signup and view all the answers

    How long after a streptococcal infection do antistreptolysin O levels typically rise?

    <p>1-3 weeks after infection</p> Signup and view all the answers

    Why is the Antistreptolysin O test performed?

    <p>For diagnosis of post-streptococcal conditions</p> Signup and view all the answers

    What is the first step in the ASO tube testing procedure?

    <p>Prepare serial dilutions of patient serum</p> Signup and view all the answers

    In Tube 1 of the ASO testing, what is the dilution ratio used?

    <p>1:10</p> Signup and view all the answers

    What can elevated antistreptolysin O levels indicate in a patient?

    <p>Bacterial endocarditis or rheumatic fever</p> Signup and view all the answers

    What happens when streptococcal antigens remain in circulation after treatment?

    <p>They cause an autoimmune response</p> Signup and view all the answers

    Which of the following conditions can the ASO test help diagnose?

    <p>Rheumatic heart disease</p> Signup and view all the answers

    Study Notes

    Identifying Cocci

    • Catalase negative cocci can be identified by analyzing their hemolytic patterns on blood agar plates.
    • Viridans streptococci are resistant to optochin.
    • Enterococci can grow in 6.5% sodium chloride solution.
    • Streptococcus bovis is non-hemolytic and cannot grow in a highly salinic solution.

    Hemolytic Patterns

    • β-hemolytic: indicates complete lysis of red blood cells (RBCs), seen as a clear zone around the colonies.
    • α-hemolytic: partial lysis of RBCs, producing a greenish discoloration around the colonies.
    • γ-hemolytic: no lysis of RBCs, no change in the surrounding medium.

    Lancefield’s Grouping

    • A serological method for classifying streptococci into groups.
    • Based on the presence of polysaccharides or sugars, and teichoic acid antigens in the bacterial cell wall.
    • Streptococci are designated by letter based on their group.

    Streptococcus pyogenes

    • A β-hemolytic streptococcus associated with various suppurative infections.
    • Virulence factors:
      • Protein M: limits phagocytosis, prevents complement fixation, mediates adhesion to host cells.
      • DNAse: reduces host immune response, allows bacteria to use nucleic acids as a nutrient source.
      • Streptokinase: converts plasminogen to plasmin, allowing lysis of fibrin and bacterial metastasis.
      • Hyaluronidase: spreading factor, allows bacterial dissemination through tissue.
      • Pyrogenic exotoxin: superantigen, causes Streptococcal Toxic Shock Syndrome.
      • Streptolysin: causes tissue death by inducing release of lysosomal contents after ingestion by phagocytes.
        • Streptolysin O: immunogenic, oxygen labile.
        • Streptolysin S: non-immunogenic, oxygen stable.

    Antistreptolysin O (ASO) Testing

    • ASO is a specific neutralizing antibody produced against streptolysin O of S.pyogenes.
    • Levels rise 1-3 weeks after an infection (not useful for diagnosing acute streptococcal infection).
    • Utilized for diagnosing post-streptococcal conditions like glomerulonephritis, rheumatic fever, rheumatic heart disease, and bacterial endocarditis.

    ASO Tube Testing (Semi-Quantitative, Neutralization Test)

    • Serial dilutions of patient serum are made in test tubes.
    • A positive reaction displays fine flocculation (agglutination) within 2-3 minutes.
    • A negative reaction shows no agglutination.

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    Antistreptolysin O Testing (October 2024) PDF

    Description

    This quiz covers the identification of cocci bacteria, focusing on their hemolytic patterns on blood agar and classification through Lancefield's grouping. Learn about the characteristics of various streptococci and their significance in microbiology.

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