الثانية والثالثة ميكرو CVS
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الثانية والثالثة ميكرو CVS

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Questions and Answers

What is the primary function of the polysaccharide capsule of S. agalactiae?

  • Facilitates spore formation
  • Promotes motility
  • Resists phagocytosis (correct)
  • Increases oxygen consumption

    • Which of the following tests is used to identify Group B Streptococci?

  • CAMP test (correct)
  • Bacitracin sensitivity test
  • Methyl red test
  • Urease test

    • Which disease is primarily associated with Group D Streptococci?

  • Acute otitis media
  • Neonatal meningitis
  • Urinary tract infections (correct)
  • Pneumonia

    • In which environment is Group B Streptococci typically found?

    <p>Oral and vaginal flora</p> Signup and view all the answers

    What morphology and arrangement do Gram-positive S. agalactiae display?

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

    Which of the following is a characteristic culture requirement for S. agalactiae?

    <p>Facultative anaerobe with optimum temperature of 37°C</p> Signup and view all the answers

    What is a common serological test for identifying the capsule of S. agalactiae?

    <p>Quellung reaction</p> Signup and view all the answers

    Which of the following diseases is least likely associated with S. agalactiae?

    <p>Chronic obstructive pulmonary disease</p> Signup and view all the answers

    What is a characteristic clinical feature of scarlet fever?

    <p>Skin rash and stomatitis</p> Signup and view all the answers

    Which of the following infections are classified as suppurative infections?

    <p>Tonsillitis and pneumonia</p> Signup and view all the answers

    What type of test is primarily used for diagnosing pharyngitis?

    <p>Throat swab</p> Signup and view all the answers

    What is an important aspect of the culture requirements for growing S. pyogenes?

    <p>Facultative anaerobe with 37C as optimal temperature</p> Signup and view all the answers

    Which of the following tests can differentiate S. pyogenes from other beta-hemolytic streptococci?

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

    Which condition can result as a post-streptococcal sequelae?

    <p>Acute rheumatic fever</p> Signup and view all the answers

    What is the main characteristic of erysipelas as an invasive infection?

    <p>It can lead to severe complications like bacteremia.</p> Signup and view all the answers

    What pathological mechanism is thought to contribute to post-streptococcal conditions?

    <p>Autoimmune response due to cross-reactivity</p> Signup and view all the answers

    What indicates a positive reaction when testing for Streptococcus pyogenes?

    <p>Clumping of latex particles in the A circle</p> Signup and view all the answers

    What is the principle behind the Schultz-Charlton reaction?

    <p>Neutralization of the toxin with specific antitoxins</p> Signup and view all the answers

    If an individual has a positive Dick test result, what is expected to be observed?

    <p>Redness and swelling in the test arm</p> Signup and view all the answers

    What indicates an immune response in the Dick test?

    <p>No reaction in the test arm</p> Signup and view all the answers

    What does a significant titer level of Anti-streptolysin O (ASO) indicate?

    <p>Titer of 200 or more Todd units</p> Signup and view all the answers

    Which of the following is NOT a specific test used for diagnosis of rheumatic fever?

    <p>C-reactive protein test</p> Signup and view all the answers

    What is a characteristic of the pseudo-reaction in the Dick test?

    <p>Disappearing reaction in both arms simultaneously</p> Signup and view all the answers

    Why is no vaccine currently available for rheumatic fever?

    <p>Difficulty in target antigen identification</p> Signup and view all the answers

    Which classification is used to differentiate types of hemolysis in streptococci?

    <p>Lancefield classification</p> Signup and view all the answers

    What is the arrangement of streptococci bacteria?

    <p>Chains or pairs</p> Signup and view all the answers

    Which of the following streptococci are classified as β-hemolytic?

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

    What is a key virulence factor associated with S. pyogens?

    <p>M-protein that inhibits phagocytosis</p> Signup and view all the answers

    Which enzyme produced by streptococci is responsible for lysis of fibrin?

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

    What type of hemolysin is Streptolysin O classified as?

    <p>Oxygen-labile and antigenic</p> Signup and view all the answers

    Which characteristic is NOT typical of streptococci?

    <p>Gram negative</p> Signup and view all the answers

    Which of the following statements best describes the capsule of S. pyogens?

    <p>Non-antigenic and made of hyaluronic acid</p> Signup and view all the answers

    What characteristic appearance do colonies of the organism on blood agar show?

    <p>Small with central depression and zones of α-hemolysis</p> Signup and view all the answers

    What biochemical reaction differentiates S. pneumoniae from S. viridans?

    <p>Sensitive to optochin</p> Signup and view all the answers

    What type of reaction occurs when specific polyvalent antibodies are added to S. pneumoniae?

    <p>Quellung reaction</p> Signup and view all the answers

    Which group of individuals is most recommended to receive the pneumococcal vaccine?

    <p>Young children, elderly, and debilitated persons</p> Signup and view all the answers

    What characteristic distinguishes S. pneumoniae in terms of pathogenicity in mice?

    <p>Pathogenic causing death in 18-48 hours due to septicaemia</p> Signup and view all the answers

    What is the Gram stain morphology of S. pneumoniae?

    <p>Gram positive cocci in pairs or short chains</p> Signup and view all the answers

    What is a common predisposing factor for bacterial endocarditis caused by S. viridans?

    <p>Dental manipulation associated with transient bacteremia</p> Signup and view all the answers

    How does S. pneumoniae behave in terms of optochin sensitivity compared to S. viridans?

    <p>S. pneumoniae is sensitive while S. viridans is resistant</p> Signup and view all the answers

    Which clinical feature is associated with scarlet fever?

    <p>Skin rash and stomatitis</p> Signup and view all the answers

    What type of infections fall under suppurative infections caused by S. pyogenes?

    <p>Respiratory, skin, and toxic infections</p> Signup and view all the answers

    How does one identify S. pyogenes in culture?

    <p>Growth on blood agar with beta-hemolysis</p> Signup and view all the answers

    Which condition is a recognized post-streptococcal sequelae?

    <p>Acute rheumatic fever</p> Signup and view all the answers

    What mechanism is thought to contribute to post-streptococcal diseases?

    <p>Antibodies cross-reacting with host tissues</p> Signup and view all the answers

    What is the significance of the bacitracin sensitivity test for S. pyogenes?

    <p>It helps differentiate it from other beta-hemolytic streptococci</p> Signup and view all the answers

    What characterizes the clinical presentation of streptococcal toxic shock-like syndrome?

    <p>Similar clinical picture to staphylococcal TSS</p> Signup and view all the answers

    What timing is observed for the onset of post-streptococcal sequelae?

    <p>1-3 weeks after an acute streptococcal illness</p> Signup and view all the answers

    What is the main reason the polysaccharide capsule of S. agalactiae is considered a virulence factor?

    <p>It resists phagocytosis by immune cells.</p> Signup and view all the answers

    Which of the following is NOT true about the CAMP test related to S. agalactiae?

    <p>A positive result indicates the presence of S. pneumoniae.</p> Signup and view all the answers

    What differentiates Group D Streptococci from Group B Streptococci in culture characteristics?

    <p>Group D Streptococci can grow on ordinary media.</p> Signup and view all the answers

    Which infection is predominantly caused by Group B Streptococci?

    <p>Neonatal septicemia</p> Signup and view all the answers

    What type of bacteria does the Quellung reaction specifically test for?

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

    What culture condition is ideal for growing S. agalactiae?

    <p>Facultative anaerobic environment with normal CO2 levels.</p> Signup and view all the answers

    The presence of which of the following indicates faecal pollution in water?

    <p>Group D Streptococci.</p> Signup and view all the answers

    What is a significant indicator of susceptibility in a Dick test for scarlet fever?

    <p>Redness and swelling in the test arm with no reaction in the control arm.</p> Signup and view all the answers

    What is one primary function of M-proteins in Streptococcus pyogenes?

    <p>Enhance adherence to host tissues</p> Signup and view all the answers

    What is the importance of the capsular swelling reaction in identification?

    <p>It helps in confirming the serotype of the bacteria.</p> Signup and view all the answers

    Which test assesses susceptibility to scarlet fever through the irritation caused by erythrogenic toxin?

    <p>Dick test</p> Signup and view all the answers

    What defines a pseudo-reaction in the Dick test?

    <p>Reaction that disappears in both arms simultaneously.</p> Signup and view all the answers

    Which of the following is an enzyme produced by streptococci that acts as a spreading factor?

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

    What does a significant titer level of Anti-streptolysin O (ASO) greater than 200 Todd units indicate?

    <p>Active streptococcal infection.</p> Signup and view all the answers

    What characterizes Streptolysin O in terms of its reaction to oxygen?

    <p>Oxygen-labile and antigenic</p> Signup and view all the answers

    Which laboratory finding can be classified as a non-specific test for rheumatic fever?

    <p>C-reactive protein (CRP)</p> Signup and view all the answers

    Which characteristic differentiates α-hemolytic streptococci from β-hemolytic streptococci?

    <p>Type of hemolysis exhibited</p> Signup and view all the answers

    In the Schultz-Charlton reaction, what is the principle behind the disappearance of the rash?

    <p>Neutralization of erythrogenic toxin with antierythrogenic toxin.</p> Signup and view all the answers

    Which group of streptococci is known for its association with the highest number of surface protein variants?

    <p>Group A (S. pyogenes)</p> Signup and view all the answers

    In terms of biological classification, what does the Lancefield classification system use to differentiate streptococci species?

    <p>Carbohydrate antigens</p> Signup and view all the answers

    What does high levels of C-reactive protein (CRP) indicate in a clinical setting?

    <p>Presence of an inflammatory condition.</p> Signup and view all the answers

    What is the primary specimen type used for the diagnosis of scarlet fever?

    <p>Throat swab</p> Signup and view all the answers

    What is a common feature of capsulated streptococci in terms of their immune evasion?

    <p>Inhibiting phagocytosis</p> Signup and view all the answers

    Which of the following streptococci is classified as non-typable based on hemolysis?

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

    What is the appearance of colonies of S. pneumoniae on blood agar?

    <p>Small with central depression surrounded by α-hemolysis</p> Signup and view all the answers

    Which biochemical characteristic can be used to differentiate S. pneumoniae from S. viridans?

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

    What does a positive Quellung reaction indicate?

    <p>Swelling of the capsule with antibodies</p> Signup and view all the answers

    What is the pathogenicity of S. pneumoniae in mice upon intraperitoneal injection?

    <p>Death in 18-48 hours due to septicaemia</p> Signup and view all the answers

    Which group of individuals is commonly recommended to receive the pneumococcal vaccine?

    <p>Young children and the elderly</p> Signup and view all the answers

    Which of the following conditions is S. viridans specifically associated with?

    <p>Acute ulcerative endocarditis</p> Signup and view all the answers

    What is the morphology of S. pneumoniae when observed under a Gram stain?

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

    How does S. pneumoniae react to optochin sensitivity compared to S. viridans?

    <p>S. pneumoniae is sensitive, S. viridans is resistant</p> Signup and view all the answers

    Study Notes

    Group B Streptococci (Streptococcus agalactiae)

    • Found in normal vaginal, oral, and gastric flora
    • Causes neonatal septicemia, pneumonia, meningitis
    • CAMP test positive, bacitracin resistant

    Group D Streptococci (Streptococcus faecalis) (Enterococci)

    • Present in the gastrointestinal tract
    • Considered an indicator of fecal pollution in water
    • Causes urinary tract infections, wound infections
    • Bile esculin hydrolysis test: positive

    Streptococcus agalactiae (Group B Streptococci) Morphology and Characteristics

    • Gram-positive, lancet-shaped cocci
    • Arranged in diplococci
    • Non-motile
    • Non-spore-forming
    • Capsulated:
      • The capsule appears as unstained halos around the cocci.
      • Main virulence factor: The polysaccharide capsule resists phagocytosis.
      • Serotyping: Classified into ≥ 80 serotypes based on the antigenic structure of the capsule.
      • Detection: Can be detected by a serological test (Quellung reaction = capsular swelling reaction)

    Streptococcus agalactiae (Group B Streptococci) Diseases

    • Most frequent cause: Pneumonia and its complications, including bacteremia, meningitis, septic arthritis, and endocarditis.
    • Common cause: Sinusitis, acute otitis media, and conjunctivitis.

    Streptococcus agalactiae (Group B Streptococci) Samples

    • Sputum

    Streptococcus agalactiae (Group B Streptococci) Culture

    • Culture requirements:
      • Oxygen: Facultative anaerobes
      • Temperature: Optimum growth at 37°C
      • Carbon Dioxide: Grow in normal CO2 concentration, but grow better in excess CO2.
    • Culture media:
      • Ordinary media: Cannot grow on it.

    Streptococcus pyogenes (Group A Streptococci) Morphology and Characteristics

    • Gram-positive cocci
    • Arranged in chains or pairs
    • Facultative anaerobes
    • Non-motile
    • Non-spore-forming
    • Capsulated
    • Cell Wall:
      • Carbohydrate (c) antigen: Used for Lancefield classification (Group A = S. pyogenes)
      • Protein antigens: M, R, and T-proteins
        • M-proteins: > 50 types of S.pyogenes, important virulence factors
        • R & T-proteins: Used as epidemiologic markers, no role in virulence

    Streptococcus pyogenes (Group A Streptococci) Capsule

    • Non-antigenic
    • Composed of hyaluronic acid, similar to host connective tissue

    Streptococcus pyogenes (Group A Streptococci) Virulence Factors:

    • Cell Wall Associated Proteins and Polymers:
      • M-protein and Lipoteichoic acid: Adherence to cells, inhibit phagocytosis.
      • M-protein and hyaluronic acid capsule: Inhibits phagocytosis
    • Enzymes:
      • Streptokinase: Lysis of fibrin
      • Streptodornase: Lysis of nucleic acid
      • Hyaluronidase: Spreading factor that digests hyaluronic acid
    • Toxins:
      • Streptolysin S: Oxygen-stable, non-antigenic hemolysin.
      • Streptolysin O: Oxygen-labile, antigenic hemolysin.
        • Antibodies to Streptolysin O are used in the diagnosis of streptococcal diseases.

    Streptococcus pyogenes (Group A Streptococci) Exotoxins

    • Erythrogenic toxin:
      • Causes the rash of scarlet fever.
      • Associated with a toxic shock-like syndrome.

    Streptococcus pyogenes (Group A Streptococci) Diseases

    • Suppurative Infections:
      • Respiratory infections: Tonsillitis, sinusitis, otitis media, and pneumonia.
      • Skin infections: Superficial (impetigo) or deep (cellulitis).
      • Invasive infections: Bacteremia, osteomyelitis, wound infections, meningitis, endocarditis, puerperal sepsis, and erysipelas.
    • Toxogenic Diseases:
      • Streptococcal toxic shock-like syndrome (STSS): Similar to Staphylococcal TSS.
      • Scarlet fever: Affects children; clinical picture includes fever, skin rash, and stomatitis (strawberry tongue).
    • Post-Streptococcal Sequelae:
      • Definition: Infections can cause sequelae, such as acute rheumatic fever and acute glomerulonephritis.
      • Timing: Begin 1-3 weeks after an acute streptococcal illness.
      • Pathogenesis: Poorly understood, but thought to be immune-mediated (autoimmune response).

    Streptococcus pyogenes (Group A Streptococci) Diagnosis

    • Diagnosis of suppurative infection:
      • Samples:
        • Blood: Puerperal sepsis, erysipelas, endocarditis, bacteremia.
        • Throat swab: Pharyngitis, scarlet fever.
        • Sputum: Pneumonia.
    • Gram Stain:
      • Direct film stained with Gram stain for characteristic morphology.
    • Culture:
      • Culture requirements:
        • Oxygen: Facultative anaerobes.
        • Temperature: 37°C
        • Carbon Dioxide: Grow in normal atmospheric CO2 concentration, but 10% CO2 enhances growth.
      • Culture media:
        • Ordinary media: Cannot grow on it.
        • Enriched media: Grow on blood agar, colonies are small (pinpoint), translucent, and surrounded by zones of β-hemolysis.
    • Identification of Growth (Biochemical Reactions):
      • Film stained by Gram stain: Shows morphology.
      • Catalase negative: Differentiates from Staphylococci.
      • Bacitracin sensitivity: Sensitive (distinguishes from other beta-hemolytic streptococci which are bacitracin resistant).
      • Specific identification of S. pyogenes: By reaction with specific antibodies.

    Streptococcus pyogenes (Group A Streptococci) Serology

    • Clumping of latex particles indicates it is a Lancefield group A Streptococcus (Streptococcus pyogenes).

    Streptococcus pyogenes (Group A Streptococci) Diagnosis of Scarlet Fever

    • Specimen: Throat swab, examined as mentioned above.
    • Schultz-Charlton reaction:
      • Principle: Neutralization of the toxin with specific antitoxins.
      • Procedure: Injection of antierythrogenic toxin into a rash; rash disappears within 6-12 hours.
    • Dick test (Test of Susceptibility):
      • Uses: To assess susceptibility to scarlet fever.
      • Principle: Erythrogenic toxin is irritating and causes a local reaction when injected intradermally, unless neutralized by specific antitoxin.
      • Method:
        • 0.1 ml of toxin is injected intradermally into one forearm (test arm).
        • The same amount of heated toxin (detoxified) is injected into the other forearm (control arm). Read results within 4-7 days.
      • Interpretation:
        • Positive test (susceptible): Redness and swelling in the test arm that reaches maximum after 4-7 days and disappears gradually. No reaction in the control arm.
        • Negative test (immune): No reaction on both arms.
        • Pseudo-reaction (hypersensitivity): Reaction appears and disappears in both arms at the same time.

    Streptococcus pyogenes (Group A Streptococci) Diagnosis of Rheumatic Fever

    • Clinical:
      • Clinical picture and history of preceding streptococcal infections.
      • Elevated C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR).
    • Non-specific tests:
      • CRP is a non-specific protein that appears in serum during active rheumatic fever and other inflammatory conditions.
    • Specific tests:
      • Anti-streptolysin O (ASO):
        • Purpose: To determine the titer of antibodies to streptolysin O toxin.
        • Significance: A titer of 200 or more Todd units is significant.
      • Other tests: Anti-DNase, anti-hyaluronidase, anti-streptokinase.
    • Vaccine: Currently, no vaccine is available.

    Streptococcus pneumoniae Morphology and Characteristics

    • Habitat: Normal oral flora.
    • Gram stain: Gram-positive cocci arranged in pairs or short chains.
    • Morphology:
      • Non-spore-forming.
      • Non-motile
      • Non-capsulated.
    • Culture:
      • Produces α-hemolytic small colonies on blood agar.
      • Resistant to optochin
      • Not bile soluble.

    Streptococcus pneumoniae Diseases

    • Bacterial endocarditis:
      • Especially if heart valves are damaged by previous rheumatic fever or congenital heart disease.
      • Dental manipulation associated with transient bacteremia is a common predisposing factor.

    Streptococcus pneumoniae vs. Streptococcus viridans: Characteristics and Comparisons

    Characteristic Streptococcus pneumoniae Streptococcus viridans
    Inulin fermentation Positive Negative
    Bile solubility Soluble Not soluble
    Optochin sensitivity Sensitive Resistant
    Capsule and Quelling Positive (Quelling reaction) Negative
    Mice Pathogenicity Pathogenic Non-pathogenic
    Rheumatic Endocarditis Subacute Bacterial Endocarditis Acute Ulcerative Endocarditis

    Post-Streptococcal Infections

    • Group A beta-hemolytic streptococci: Causes post-streptococcal infections (e.g., rheumatic fever, glomerulonephritis).
    • Streptococcus viridans: Associated with subacute bacterial endocarditis.
    • Streptococcus pyogenes: Causes acute ulcerative endocarditis.
    • Streptococcus faecalis: Not associated with endocarditis.
    • *Important Note- ** There may be a few additional details that are not fully fleshed out here, but this provides a comprehensive overview of the key information contained in the text, as requested.

    Group B Streptococci (Streptococcus agalactiae)

    • Normal vaginal, oral, and gastric flora
    • Causes: neonatal septicemia, pneumonia, meningitis
    • CAMP test positive
    • Bacitracin resistant
    • Gram-positive lancet-shaped cocci
    • Diplococci
    • Non-motile
    • Non-spore forming
    • Capsulated (appears as unstained halos around cocci)
    • Main virulence factor: polysaccharide capsule (resists phagocytosis)
    • Classified into 80 serotypes based on capsule antigenic structure
    • Can be detected by the Quellung reaction (capsular swelling reaction)
    • Frequent cause of pneumonia and complications like bacteremia, meningitis, septic arthritis, and endocarditis
    • Also causes sinusitis, acute otitis media, and conjunctivitis
    • Grows in normal CO2 concentration, but better in excess CO2
    • Culture Media:
      • Cannot grow on ordinary media
      • Grown on enriched media (blood agar)

    Group D Streptococci (Streptococcus Faecalis) (Enterococci)

    • Present in the GIT
    • Considered an indication of fecal pollution of water
    • Causes: urinary tract infections, wound infections
    • Bile esculin hydrolysis test: positive

    Streptococcal Infections

    • Classified into 18 different sero-groups (A → U) based on carbohydrate antigen (C-antigen) on cell wall
    • Streptococcus pyogenes (Group A)
    • Streptococcus agalactia (Group B)

    Streptococcus pyogenes (Group A)

    • Gram-positive cocci arranged in long chains

    • Non-motile, non-spore forming

    • Capsulated

    • Virulence Factors:

      • Cell Wall Associated Proteins and Polymers:
        • M protein & Lipoteichoic acid: Adherence to cells, inhibit phagocytosis
        • M protein & Hyaluronic Acid Capsule: Inhibit phagocytosis
      • Enzymes:
        • Streptokinase: Lysis of fibrin
        • Streptodornase: Lysis of nucleic acid
        • Hyaluronidase: Spreading factor (digests hyaluronic acid)
      • Toxins:
        • Streptolysin S: Oxygen-stable, non-antigenic, hemolysin
        • Streptolysin O: Oxygen-labile, antigenic hemolysin (antibodies to streptolysin O used in diagnosis of streptococcal diseases)
        • Erythrogenic toxin: Causes the rash of scarlet fever and has been associated with toxic shock-like syndrome

    • Diseases:

      • Suppurative Infections:
        • Respiratory Infections: Tonsillitis, sinusitis, otitis media, pneumonia
        • Skin Infections: Superficial (impetigo) or deep (cellulitis)
        • Invasive Infections: Bacteremia, osteomyelitis, wound infections, meningitis, endocarditis, puerperal sepsis, erysipelas
      • Toxogenic Diseases:
        • Streptococcal Toxic Shock-like Syndrome (TSS): Similar to staphylococcal TSS
        • Scarlet fever: Affects children, causing fever, skin rash, and stomatitis (strawberry tongue)
      • Post-streptococcal Sequelae:
        • Occur 1–3 weeks after a streptococcal illness
        • Mechanism: Immune-mediated (e.g., antibodies produced during infection cross-react with host tissues)
        • Examples:
          • Acute rheumatic fever
          • Acute glomerulonephritis

    Streptococcus pneumoniae (Pneumococcus)

    • Gram-positive cocci arranged in pairs or short chains

    • Non-motile, non-spore forming, and non-capsulated

    • α-hemolytic (small colonies on blood agar)

    • Resistant to optochin and not bile-soluble

    • Causes: Pneumonia, bacteremia, meningitis, otitis media

    • Specific Identification:

      • Film stained by Gram stain to show morphology
      • Biochemical reactions: Ferment inulin, bile-soluble
      • Sensitive to optochin
      • Pathogenicity to mice: Intraperitoneal injection of culture into mice leads to death within 18–48 hours due to septicemia
      • Capsular swelling reaction (Quellung reaction): Swelling of the capsule after addition of specific polyvalent antibodies

    • Vaccination:

      • Pneumococcal Vaccine: Contains capsular material from 23 pathogenic strains
      • Recommended for young children, elderly, and debilitated persons

    Streptococcus viridans

    • Gram-positive cocci
    • Non-spore forming
    • Non-motile
    • Produces α-hemolytic small colonies on blood agar
    • Resistant to optochin (distinguishes it from S. pneumoniae)
    • Bile insoluble
    • Considered normal oral flora
    • Causes:
      • Dental caries
      • Bacterial endocarditis (especially if heart valves have been damaged by rheumatic fever or congenital heart disease)

    Differentiating Streptococci

    Streptococcus pneumoniae Streptococcus viridans
    Inulin Fermentation Positive Negative
    Bile Solubility Soluble Not soluble
    Optochin Sensitivity Sensitive Resistant
    Capsule & Quellung Reaction Positive Negative
    Mice Pathogenicity Pathogenic Non pathogenic
    Endocarditis Subacute bacterial endocarditis Acute ulcerative endocarditis

    Diagnosis of Streptococcal Infections

    Diagnosis of Suppurative Infection

    • Samples:
      • Blood: Puerperal sepsis, erysipelas, endocarditis, bacteremia
      • Throat swab: Pharyngitis, scarlet fever
      • Sputum: Pneumonia
    • Gram Staining:
      • Direct film stained for characteristic morphology
    • Culture:
      • Requirements: Facultative anaerobes, optimum temperature 37°C, normal atmospheric CO2 concentration (10% CO2 enhances growth)
      • Media: Cannot grow on ordinary media, grows on blood agar (small, translucent colonies surrounded by zones of β-hemolysis)
    • Identification:
      • Film stained with Gram stain to show morphology
      • Biochemical reactions: Catalase negative
      • Bacitracin sensitivity: Sensitive (differentiates from other β-hemolytic streptococci, which are resistant)
      • Specific identification of S. pyogenes: Reaction with specific antibodies
      • Serology: Latex agglutination test (Clumping of latex particles in the "A" circle indicates Group A)

    Diagnosis of Scarlet Fever

    • Specimen: Throat swab
    • Schultz-Charlton Reaction
      • Principle: Neutralization of erythrogenic toxin with specific antitoxin
      • Procedure: Injection of antierythrogenic toxin into the rash causes rash disappearance within 6–12 hours.
    • Dick Test (Test of Susceptibility)
      • Uses: Assess susceptibility to scarlet fever
      • Principle: Erythrogenic toxin is irritating and causes a local reaction when injected intradermally unless neutralized by specific antitoxin
      • Method: 0.1 ml of toxin intradermally in one forearm (test arm); same amount of heated (detoxified) toxin in the other forearm (control arm)
      • Interpretation:
        • Positive Test: Redness and swelling in the test arm that reaches maximum after 4–7 days and disappears gradually; No reaction in the control arm
        • Negative Test: No reaction in both arms
        • Pseudo-reaction (hypersensitivity): Reaction appears and disappears in both arms simultaneously

    Diagnosis of Rheumatic Fever

    • Clinical Picture and History: History of preceding streptococcal infections
    • Non-specific Tests:
      • C-reactive protein (CRP): Increased in active rheumatic fever as well as inflammatory conditions
      • ESR: Elevated
    • Specific Tests:
      • Increase in the titer of:
        • Anti-streptolysin O (ASO): Used to determine the titer of antibodies to streptolysin O toxin ( titer of 200 or more Todd units is significant)
        • Anti-DNase
        • Anti-hyaluronidase
        • Anti-streptokinase
    • No vaccine is currently available for streptococcal infections.

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