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Bacteriology > Streptococcus (Pt. 1) > Flashcards

Streptococcus (Pt. 1) Flashcards

1
Q

What distinguishes Staphylococci from streptococci?

A

Streptococci are catalase negative.

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2
Q

How are streptococci arranged?

A

Streptococci are arranged in linear arrangements.

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3
Q

List the characteristics of streptococcoccaeceae family

A
  • Gram Positive cocci
  • Arranged linearly in pairs or chain
  • Catalase negative
  • Facultative anaerobic
  • Some are encapsulated
  • Non- motile
  • Non- sporulating
  • May be part of commensal flora
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4
Q

What are the methods of classification of streptococci?

A

1) Lancefield cell wall carbohydrates: Group A, B, D…
2) Type of hemolysis (alpha, beta, gamma)
3) Biochemical properties

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5
Q

What are the lancefield classification of different streptococci?

A

Group A: S. pyogenes
Group B: S. agalactiae
Group D: Enterocci, S. Bovis

Non- Lancefield
Viridans Group: S. mutans
S. pneumonia

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6
Q

What is the Lancefield group carbohydrate A composed of?

A

Rhamnose and N-acetylglucosamine

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7
Q

How do you identify the Lancefield antigen?

A

Precipitin test:
1) Lysis of streptococcal cells with enzymes that destroy the cell wall and expose the antigens
2) Treat the sample with the antisera specific to the antigen and see agglutination

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8
Q

What is special about the GAS capsule? How does it appear on agar?

A

It is made of hyaluronic acid, which is the same component as our skin connective tissues. Therefore, it is a poor immunogen that does not elicit an immune response (no antibodies are observed). They appear as mucoid (mucus-like colonies) on agar plates.

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9
Q

What are the Virulence factors of GAS capsule?

A
  • Non antigenic
  • Hides its own antigens
  • Prevents opsonized phagocytosis by neutrophils and macrophages
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10
Q

What is the major cause of antigenic drift and shift in GAS?

A

M protein

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11
Q

How does M protein inhibit phagocytosis?

A

The M protein antigen binds fibrinogen in serum blocking the binding of its complement antibody. However, the antibody against M protein is durable.

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12
Q

Which adhesins facilitate the binding of the bacteria to fibronectin?

A

Fibronectin binding protein (F protein) and Lipoteichoic acid

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13
Q

What is steptolysin S?

A

Streptolysin S is an oxygen- labile leukocidin that lyses leukocytes, erythrocytes and platelets. They exhibit the beta hemolysis on blood agar.

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14
Q

What is streptolysin O?

A

Streptolysin O is an oxygen-labile leukocidin: lyse erythrocytes, leukocytes, and
platelets. It is active in anaerobic environments

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15
Q

Why does Streptococcus release hyaluronidase? How does it affect the bacteria?

A

Hyaluronidase can digest host connective tissue hyaluronic acid, allowing it to penetrate the tissue. However, it also digests the organism’s own capsule.

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16
Q

Why does streptococcus release DNase?

A

DNase allows streptococcus to reduce the viscosity of abscess material (pus, sebum) facilitating the spread of the bacteria in these tissues

17
Q

How do streptokinases released by streptococcus bacteria dissolve fibrin clots?

A

Streptokinase cleaves plasminogen to plasmin, which is a protease that dissolves fibrin back into fibrinogen

18
Q

What do proteases released by streptococci do to the body?

A

Proteases cause soft tissue necrosis and toxic shock syndrome
Proteases also cleave immunoglobulins and complement systems preventing antibody-mediated phagocytosis

19
Q

What are the SPE exotoxins released by streptococci?

A

The four SPE pyogenic exotoxins, or erythrogenic toxins are recognized as SPE A, SPE B, SPE C , SPE F

  • These toxins act as super antigens
  • SPE A and SPE C are especially scarlatinal toxins and are encoded by lysogenic phages. When these toxins are disseminated in the blood, they cause scarlet fever.
20
Q

What is the general incubation period of Streptococcal infections?

A

IP: 2-4 days

21
Q

Which is primarily a disease of children?

A

Pharyngitis

22
Q

How is streptococcus bacteria usually spread?

A

The pathogen is spread from person to person through respiratory droplets particularly during the winter months. (Crowding, daycare facilities).

23
Q

What are suppurative conditions and not suppurative conditions?

A

Suppurative conditions are active infections that are associated with pus production. They include pharyngitis, tonsillitis, skin infections, etc.
Non-suppurative conditions include rheumatic fever and glomerulonephritis

24
Q

What is usually the age group that is diagnosed with GAS pharyngitis?

A

5-15 years old children. Strep often colonizes asymptomatic persons (high in chidren)

25
Q

How is pharyngitis transmitted?

A

Transmission: droplets, saliva or nasal secretions

26
Q

What are the symptoms of pharyngitis?

A

1-Sore throat (2-4 days post exposure),malaise, high grade fever, headache,
2-Lymphoid hyperplasia of the posterior portion of the pharynx
• enlarged tonsils
• Intense nasopharyngitis
• tonsillitis
• redness/edema of mucus membranes with purulent exudates
3- Lymph nodes enlarge
4-High CRP and WBC count

27
Q

How does a blood specimen showcase GAS pharyngitis?

A

High CRP and WBC count

28
Q

What is the most common complication of pharyngitis?

A

Scarlet fever

29
Q

What is scarlet fever?

A

Severe pharyngitis, skin infections and high grade fever.

30
Q

How does scarlet fever present on the body?

A
  • Red rash on trunk, may spread to extremities after 24h of illness (Scarlet = red)
  • Diffuse red spots over upper part of the chest-spread to remainder of the trunk, neck
    and extremities, face flushed.
  • Pharyngitis, tonsillitis, hemorrhagic spots on the hard and soft palates (white
    strawberry tongue)
31
Q

How long does the rash of scarlet fever last? How does it present finally?

A

The rash disappears over the next 5 to 7 days and is followed by desquamation

Bacteriology (11 decks)

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