Streptococcus Pneumoniae (Pneumococcus)
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📖 About
- 🦠 Streptococcus pneumoniae (Pneumococcus).
- Major cause of community-acquired pneumonia and bacterial meningitis in adults.
- Resistance to penicillin is increasing worldwide.
🔬 Characteristics
- Alpha-haemolytic, Gram-positive diplococcus, lanceolate-shaped.
- Heavily encapsulated with carbohydrate capsule → ↑ pathogenicity.
- Catalase-negative, facultative anaerobe, enhanced growth with 10% CO₂.
- Colonies have “draughtsman” appearance with greenish discolouration (alpha-haemolysis).
🧪 Virulence Factors
- 💉 Capsule resists phagocytosis.
- 🧾 Produces IgA1 protease → breaks down mucosal IgA.
- ☠️ Exotoxin pneumolysin → damages neutrophils and cilia.
- ❗ Patients with splenectomy, hyposplenism, or sickle cell disease are at high risk of overwhelming sepsis.
🏠 Source
- Commensal of the upper respiratory tract (nasopharynx).
⚠️ Clinical Manifestations
- Community-acquired pneumonia (CAP) - lobar, “rust-coloured” sputum.
- Acute bacterial meningitis (esp. adults, elderly, immunocompromised).
- Otitis media, sinusitis, conjunctivitis.
- Exacerbations of COPD.
- Invasive disease: osteomyelitis, peritonitis, endocarditis, septicaemia (esp. asplenic).
🧾 Investigations
- Gram stain: lancet-shaped diplococci.
- Cultures: optochin-sensitive, bile-soluble.
- Ferments inulin.
- Detection of capsular antigens in CSF, sputum, or urine.
- Quellung reaction: capsule swelling with specific antisera.
- Over 80 capsular serotypes described.
💉 Vaccination
- Polysaccharide vaccines available (e.g. PPSV23, PCV13).
- Indicated in at-risk groups: asplenic, sickle cell, immunodeficiency, chronic heart/lung/kidney disease, older adults.
⚔️ Resistance Patterns
- Increasing resistance to penicillin (esp. outside UK).
- In UK: resistance more common to erythromycin, tetracyclines, and trimethoprim.
🧴 Sensitivity
- Most strains remain sensitive to penicillin in the UK.
💊 Treatment
- Mild: oral amoxicillin + macrolide (e.g. clarithromycin).
- Moderate to severe: start IV (e.g. co-amoxiclav + clarithromycin), switch to oral if improving after 48 h.
- Adjust antibiotics according to sensitivities and local resistance patterns.
