Streptococcus (Pt. 1) Flashcards
What distinguishes Staphylococci from streptococci?
Streptococci are catalase negative.
How are streptococci arranged?
Streptococci are arranged in linear arrangements.
List the characteristics of streptococcoccaeceae family
- 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
What are the methods of classification of streptococci?
1) Lancefield cell wall carbohydrates: Group A, B, D…
2) Type of hemolysis (alpha, beta, gamma)
3) Biochemical properties
What are the lancefield classification of different streptococci?
Group A: S. pyogenes
Group B: S. agalactiae
Group D: Enterocci, S. Bovis
Non- Lancefield
Viridans Group: S. mutans
S. pneumonia
What is the Lancefield group carbohydrate A composed of?
Rhamnose and N-acetylglucosamine
How do you identify the Lancefield antigen?
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
What is special about the GAS capsule? How does it appear on agar?
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.
What are the Virulence factors of GAS capsule?
- Non antigenic
- Hides its own antigens
- Prevents opsonized phagocytosis by neutrophils and macrophages
What is the major cause of antigenic drift and shift in GAS?
M protein
How does M protein inhibit phagocytosis?
The M protein antigen binds fibrinogen in serum blocking the binding of its complement antibody. However, the antibody against M protein is durable.
Which adhesins facilitate the binding of the bacteria to fibronectin?
Fibronectin binding protein (F protein) and Lipoteichoic acid
What is steptolysin S?
Streptolysin S is an oxygen- labile leukocidin that lyses leukocytes, erythrocytes and platelets. They exhibit the beta hemolysis on blood agar.
What is streptolysin O?
Streptolysin O is an oxygen-labile leukocidin: lyse erythrocytes, leukocytes, and
platelets. It is active in anaerobic environments
Why does Streptococcus release hyaluronidase? How does it affect the bacteria?
Hyaluronidase can digest host connective tissue hyaluronic acid, allowing it to penetrate the tissue. However, it also digests the organism’s own capsule.
Why does streptococcus release DNase?
DNase allows streptococcus to reduce the viscosity of abscess material (pus, sebum) facilitating the spread of the bacteria in these tissues
How do streptokinases released by streptococcus bacteria dissolve fibrin clots?
Streptokinase cleaves plasminogen to plasmin, which is a protease that dissolves fibrin back into fibrinogen
What do proteases released by streptococci do to the body?
Proteases cause soft tissue necrosis and toxic shock syndrome
Proteases also cleave immunoglobulins and complement systems preventing antibody-mediated phagocytosis
What are the SPE exotoxins released by streptococci?
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.
What is the general incubation period of Streptococcal infections?
IP: 2-4 days
Which is primarily a disease of children?
Pharyngitis
How is streptococcus bacteria usually spread?
The pathogen is spread from person to person through respiratory droplets particularly during the winter months. (Crowding, daycare facilities).
What are suppurative conditions and not suppurative conditions?
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
What is usually the age group that is diagnosed with GAS pharyngitis?
5-15 years old children. Strep often colonizes asymptomatic persons (high in chidren)
How is pharyngitis transmitted?
Transmission: droplets, saliva or nasal secretions
What are the symptoms of pharyngitis?
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
How does a blood specimen showcase GAS pharyngitis?
High CRP and WBC count
What is the most common complication of pharyngitis?
Scarlet fever
What is scarlet fever?
Severe pharyngitis, skin infections and high grade fever.
How does scarlet fever present on the body?
- 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)
How long does the rash of scarlet fever last? How does it present finally?
The rash disappears over the next 5 to 7 days and is followed by desquamation
