Streptococci: pneumoniae

Question 1

S.pneumoniae infections

Answer 1

• Widespread
• Capsulated: meningitis
  High HIV infections = High S.pneumoniae infections
• Can infection horses too

Question 2

Carriage and colonization of S.pneumoniae

Answer 2

• Mucosa of URT
• Can be commensal or pathogenic
• Carries can shed in nasal secretions = transmission
• Dissemination by aspiration, bacteraemia or local spread

Question 3

Risk factors for S.pneumoniae

Answer 3

• No spleen (Filters B cells)
• Viral infection
• Heart disease
• Age (v young and v old)
• Diabetes
• Alcoholism
• HIV
• Smoking

Question 4

S.pneumoniae - asymptomatic carriage

Answer 4

• Oral carriage

- All infections start with commensal carriage

Question 5

Capsule = major virulence factor

Answer 5

• Phase variation: fat/thin to fit stage of infection
• Highly immunogenic + capsule switching = antigenic variation
• Ineffective without capsule
• Inhibits complement and Ab binding

Question 6

What is fraticide?

Answer 6

S.pneumoniae can kill non-competent groups of the same species to be the dominant serovar

• Produce pneumocins
• DNA released, taken up by dominant group = selective advantage

Question 7

Place in order: Colonization

• Access to epithelial surface
• Neg charged capsule prevents phagocytosis and opsonisation - (fat capsule)
• Reach mucous membrane in nasopharynx
• Phase varitation to thin capsule for adherence

Answer 7

1) Reach mucous membrane in nasopharynx
2) Neg charged capsule prevents phagocytosis and opsonisation - (fat capsule)
3) Access to epithelial surface
4) Phase varitation to thin capsule for adherence

Question 8

S.pneumoniae: The transforming principle

Answer 8

• Natural genetic transformation/recombination
• Take up DNA from environment = selective advantage
• Capsular switching = antigenic variation

Question 9

Treatment of S.pneumoniae

Answer 9

• B-lactams (penicillin) but AMR is high
• Cefotaxime/Fluoroquinolones
• Vancomycin (but poor brain absorption)
• MDT?

Question 10

Vaccine for S.pneumoniae

Answer 10

• PPV: 90% of UK cases, T cell independent B cell response (no long term immunity), poor response in v young/old
• PCV13: Conjugate, induces T cell response, herd immunity/long term response
• vaccination against some serotypes can cause untargeted groups to rise