Streptococcus pneumoniae

Question 1

What are the characteristics of S. pneumoniae?

Answer 1

Gram-positive cocci in pairs (diplococci)
Aerotolerant but grows best under anaerobic conditions

Question 2

What is the Quellung Reaction and what is it used to characterize?

Answer 2

Reagent antibodies raised against specific polysaccharides will bind to the capsule and result in a precipitate
Used to characterize 92 capsular types

Question 3

What are the virulence factors of S. pneumoniae?

Answer 3

Capsule
Pneumolysin
Autolysin
Polysaccharide C
Proteins on the cell surface
Neuraminidase for adherence
IGA1 protease

Question 4

What is the main virulence factor for S. peneumoniae?

Answer 4

The capsule
If it is unencapsulated, then no invasive disease can occur

Question 5

What is pneumolysin?

Answer 5

A lysin that breaks down hemoglobin into a green pigment that surrounds the colonies during growth on blood and chocolate agar plates

Question 6

What does autolysin do?

Answer 6

It breaks down S pn cells and releases its component
This allows the cell to commit suicide and those antigen pieces will cause more inflammation

Question 7

What does polysaccharide C do?

Answer 7

It reacts with acute phase proteins like CRP, resists phagocytosis

Question 8

What do capsules do?

Answer 8

It prevents phagocytosis by inhibiting complement activation on the bacterial cell surface
Binds complement factor H which is a complement regulator

Question 9

How is S. pneumoniae transmitted?

Answer 9

It is often a part of commensal flora
It can also be spread by droplets or direct contact

Question 10

What are some diseases that S. pneumoniae causes?

Answer 10

Asymptomatic colonization
Pneumonia
Bacteremia/septicemia
Otitis media
Meningitis
Sinusitis
Eye infections

Question 11

Who is at risk for developing pneumococcal pneumonia?

Answer 11

Childen under 2 and adults >65
Chronic medical conditions, sickle cell anemia, HIV, transplant patients

Question 12

What are the symptoms of pneumococcal pneumonia?

Answer 12

Shaking chills
High fever
Cough
Shortness of breath
Rapid breathing
Chest pains

Question 13

What is often seen after a treated meningitis infection?

Answer 13

Neurological impairment

Question 14

What are the diagnostics of S. pneumoniae?

Answer 14

Usually Gram stain of patient sample and culture on Sheep Blood Agar
Catalase negative but produces H2O2
Grows better anaerobically than aerobically
Rapid growth in blood culture medium
Gram-positive diplococci on semi-solid media
Can look like Gram-positive streptococci in liquid media

Question 15

What are the two current vaccines for S. pneumoniae?

Answer 15

Pneumovax-23 = polysaccharide only, cheaper, given to people >65

Prevnar-20 = conjugate, covers resistant strains

Question 16

How does a polysaccharide vaccine confer protection?

Answer 16

Activates B cells but NOT T-helper cells
There is no generation of long-lasting memory and no affinity maturation of IgG antibodies
Only effective for a few years - the right cytokines are not produced

Question 17

How does a conjugate vaccine confer protection?

Answer 17

Generates a T-cell-dependent immune response that produces immunological memory
Stronger and long-lasting response with booster
Higher affinity IgG produced

Question 18

What is low-level penicillin resistance associated with?

Answer 18

Resistance to macrolides, TMP-Sulfa, quinolones, and tetracyclines