Streptococcus pneumoniae I

Streptococcus pneumoniae I

1. Pathogenesis

   • Airbourne droplets (Asymptomatic)
     • Nasopharyngeal Colonisation
       • Essential first step for disease
       • Person to person spread
       • Interactions between different bacterial species

2. Polysaccharide Capsule

   • The major pneumococcal virulence factor
     • Capsule enables bacteria to resist opsonphagocytosis
       • Resistance to Cationic Antimicrobial peptides - charge repulsion
         • Role in formation of Biofilms
           • Expression of Capsule reduces epithelial cell adherence – capsule regulation critical

3. Vaccination

   • CPS is the dominant pneumococcal surface antigen, and CPS antibodies are highly protective.
     • But protection is strictly serotype-specific: 93 serologically distinct CPS types.

4. CPS Bio-synthesis

   • glycosyl transferases assemble repeat unit by stepwise addition of activated sugar precursors to lipid carrier
     • CpsB and CpsD
       • Highly conserved
       • Present in all but 2 serotypes
       • Makes great target for drug development

5. Competence

   • Mechanism for generating genetic diversity
     • Capsular switching
       • With competence critical for spread of antibiotic resistance – target for drug development?
         • Mimic peptide pheromone – CSP
           • Mutated CSP inhibits competence