Streptococcus pneumoniae

Question 1

Biology of Streptococcus pneumoniae

Answer 1

• oval or lancer shaped
• diplococci
• alpha-hemolytic

Question 2

Virulence factors for S. pneumoniae

Answer 2

• polysaccharide capsule: protection against phagocytosis
• secretory IgA protease: stops IgA from interacting with mucin to trap and clear bacteria
• pneumolysin: a cytotoxin that binds cholesterol in host cell membrane to create pores

: destroys both ciliated epithelial cells and phagocytes

Question 3

Epidemiology for S. pneumoniae

Answer 3

• common inhabitant of the throat & nasopharynx

Question 4

Transmission of S. pneumoniae

Answer 4

• most infections are caused by endogenous spread (spread from the lungs outward)

Question 5

Who is at risk of contracting S. penumoniae?

Answer 5

patients with:

• frequent URT infections
• exposure to parental cigarette smoke
• allergies

Question 6

Diseases that can be caused by S. pneumoniae

Answer 6

• pneumonia

: typical & lobar infection

: blood-tinged “rusty” sputum (haemoptysis)

• sinusitis & otitis media
• meningitis
• bacteremia

Question 7

Mechanism of S. pneumoniae pathogenesis in pneumonia

Answer 7

• bacteria can migrate from oropharynx into lungs
• polysaccharide stops clearance, IgA protease cleaves IgA
• in alveoli, pneumococcal teichoic acid, peptidoglycan fragments, and pneumolysin mediate inflammatory responses - often causing tissue destruction

Question 8

Diagnosis of S. pneumoniae

Answer 8

• Gram-stain: gram-positive (purple appearance)
• catalase-negative
• Quellung reaction: polyvalent anticapsular antibodies are mixed with bacteria

: mixture is examined microscopically

: greater refractiveness around bacteria is a positive reaction

Question 9

Treatment of S. pneumoniae

Answer 9

• fluoroquinolone (quinolone) or
• vancomycin (glycopeptide) with
• ceftriaxone (cephalosporin)