Streptococcus pneumoniae
One-Sentence Definition
Streptococcus pneumoniae (pneumococcus) is a Gram-positive lancet-shaped diplococcus and leading cause of community pneumonia, meningitis, and otitis — virulence driven by a polysaccharide Capsule.
Taxonomy & Morphology
- α-hemolytic; optochin-sensitive; bile-soluble (classic)
- Encapsulated; many serotypes
- Gram Stain: lancet-shaped diplococci ± neutrophils
Virulence Highlights
- Polysaccharide capsule (anti-phagocytic) — vaccine target
- Pneumolysin, adhesins
- Natural competence → Transformation and mosaic PBPs
Clinical Syndromes
- Lobar pneumonia, bacteremia, meningitis
- Otitis media, sinusitis
Diagnosis
- Sputum/blood/CSF Gram + culture
- Urine pneumococcal antigen (syndrome-dependent)
- Multiplex PCR on CSF/respiratory panels
Treatment Notes (conceptual)
- Guided by local resistance and syndrome (meningitis breakpoints differ)
- Empiric regimens must cover possible penicillin/ceftriaxone non-susceptibility until AST
AMR
- Penicillin / β-lactam non-susceptibility via altered PBPs (often transformational mosaics)
- Macrolide and MDR patterns vary by serotype/region
Prevention
- Pneumococcal conjugate / polysaccharide vaccines (serotype coverage matters)
Related Notes
- Capsule · Transformation · MOC - Immunology
- Diseases: Community-Acquired Pneumonia · Bacterial Meningitis
- MOCs: MOC - Bacteriology · MOC - Diseases by System · MOC - Antimicrobial Resistance (AMR)
Active Recall
- What is the major virulence factor targeted by vaccines?
- How does transformation relate to β-lactam resistance?
- Classic Gram morphology of pneumococcus?