Microbiology · Streptococci and enterococci
Streptococcus pneumoniae !
- Bacterium
- Gram-positive
- Exam priority: high
A nose and throat bacterium behind most community pneumonia, ear infections, sinusitis and meningitis; a vaccine is in Colombia's PAI.
Updated 2026-11-01
Also called: pneumococcus
At a glance
- Gram
- Gram-positive
- Shape
- Lancet-shaped diplococci
- Oxygen
- Facultative anaerobe
- Family
- Streptococcaceae
- Stain
- Gram positive; catalase negative; alpha-haemolytic
Morphology
- Lancet-shaped Gram-positive diplococci
- Alpha (green) haemolysis on blood agar
- Polysaccharide capsule; more than 100 serotypes
Transmission
- Contact with respiratory secretions (saliva, mucus)
- Respiratory droplets from healthy carriers
- Nasopharyngeal colonisation, especially in children
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Polysaccharide capsule: the main antiphagocytic factor and the basis of vaccines
- IgA protease: degrades mucosal IgA
- Pneumolysin: damages cells and activates complement
- Autolysin: releases inflammatory cell-wall pieces
Diseases it causes
- Community-acquired pneumonia (most common bacterial cause) Community-acquired pneumonia →
- Bacterial meningitis in adults and children Bacterial meningitis →
- Acute otitis media Acute otitis media →
- Acute sinusitis Acute rhinosinusitis →
Clinical picture
- Sudden high fever, rigors, cough with rusty sputum and pleuritic pain
- Lobar consolidation on chest X-ray
- Higher risk with asplenia, sickle cell disease, HIV, the extremes of age and alcohol use
Diagnosis
- Sputum Gram stain: lancet-shaped Gram-positive diplococci
- Optochin sensitive and bile soluble
- Quellung reaction (capsule swelling with antiserum)
- Urinary C-polysaccharide antigen
- Blood and cerebrospinal fluid cultures
Treatment
Beta-lactams (amoxicillin, ceftriaxone) are the mainstay. Some strains carry altered PBPs that lower penicillin susceptibility; in meningitis ceftriaxone is combined with vancomycin until susceptibility is known. Macrolide resistance is common.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Conjugate vaccine in infants
- Vaccination of older adults and people with risk factors
- Hand and cough hygiene
Vaccine: The pneumococcal conjugate vaccine (13-valent) is part of Colombia's PAI schedule for infants; vaccines also exist for older adults and risk groups.
Test yourself
Think of the answer, then tap the question to see it.
Which two tests distinguish pneumococcus from viridans streptococci?
Optochin (pneumococcus sensitive) and bile solubility (pneumococcus soluble).
Why do people without a spleen get severe pneumococcal disease?
The spleen is key to clearing opsonised encapsulated bacteria; without it, pneumococcus spreads.
What is the mechanism of pneumococcal penicillin resistance?
Altered penicillin-binding proteins (PBPs) with lower affinity; it does not make beta-lactamase.
Which isolation precautions does a patient with pneumococcal pneumonia need?
Standard precautions only; droplet isolation is not required.
Related
Related conditions
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Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: About Pneumococcal Disease (CDC, 2024); Clinical Overview of Pneumococcal Disease (CDC, 2026); Acortamiento del Esquema (Ministerio de Salud y Protección Social, Colombia, 2025).
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Representative model, for educational purposes only.