Pneumonia II - Strep pneumonia

Question 1

Describe the epidemiology or the process of how strep works

Answer 1

It is inhaled»» asymptomatic colonization of the upper RT»>Infections such as pneumonia/otitis media
OR
Enter the blood causing bacteremia, and cause infection in distal organs such as the brain (meningitis)

Question 2

What is the pathogenesis of the strep?

Answer 2

Colonises the URT by binding to the epithelial surfaces using surface protein adhesins
Normally, secretoty IgA protects mucosal binding of the bacteria by binging to it and neutralising the bacteria. However, the pneumococcus produces IgA proteases which destroy the sIgA.
Additionally, the mucocilliary escalator usually removes the bacteria, but it fails.
Lasty, a bacterial toxin called mucolysin damages the epithelium and phagocytic cells

Question 3

How does the strep result in disease?

Answer 3

This is an extracellular pathogen
It Activates the complement system, which leads to cytokine release and inflammation.
The bacterial cell wall or capsule (antigens) may activate it via the alternate pathway.
The antibodies may activate the classical pathway.
Excessive inflammation may cause accumulation of fluid in the alveoli and diffuse consolidation of the entire lobe (lobar pneumonia)

Pneumolysin damages host cells

Question 4

S. pneumoniae _______________is key virulence factor because it prevents _____________ thereby preventing
clearance of bacteria in spleen

Answer 4

Capsule
Opsonisation

Question 5

‘_________ ‘ strains with capsule are virulent
* ‘___________ ‘ strains without capsule are avirulent

Answer 5

Smooth
Rough

Question 6

Why do pneumococci escape specific-type protection?

Answer 6

But pneumococci have ability to take up foreign DNA (called ‘competence’) so they can switch
capsule genes and thereby escape type specific protection

Question 7

Which organ is responsible for clearing opsonised bacteria?

Answer 7

Spleen

Question 8

Antibodies play major role in defense, particularly antibodies to_____________ ____________

Answer 8

Capsular polysaccharides

Question 9

What are the predisposing factors for infection? (Mechanism)

Answer 9

Previous viral infection in the resp system
Previous lung damage by smoking or pollutants
Low or nonfunctional neutrophils
reduced clearance by the spleen

Question 10

What are the predisposing factors for infection? (Multifactorial)

Answer 10

Aging- decreased immunity
* Young children: immune response to encapsulated organisms ( through T cell
independent mechanism) is poorly developed under 2 years of age
* Alcohol, malnutrition
* Diabetes mellitus
* Hospitalisation or immobility

Question 11

What other infections can be caused by S. pneumonia?

Answer 11

Local spread throughout respiratory tract:
* Otitis media
* Sinusitis
* Distant spread via bloodstream:
* Meningitis
* Arthritis
* Peritonitis

Question 12

tx of pneumococcal infections

Answer 12

Penicillin or closely related ampicillin (for intravenous use) or amoxicillin (for oral use) still
recommended as first choice for pneumococcal infections in South Africa

Question 13

Tx for resistant pneumococci

Answer 13

Higher doses of penicillin/ampicillin/amoxicillin
For meningitis: Ceftriaxone

Question 14

Vaccinations against pneumococcal infections

Answer 14

1. Polysaccharide vaccine (covers 23 serotypes) ‘older
   vaccine’ problem is that polysaccharide vaccines don’t provide
   long lasting protection, AND don’t work in young children
2. conjugate vaccine – capsule conjugated or linked to protein
   (covers 13+ serotypes) ‘new vaccine’
   Much more effective, including in infants