29 August, 2025

Streptococcus Pneumoniae

Introduction

Pneumococcus-bacteria (scientifically known as Streptococcus pneumoniae) are Gram-positive, α-hemolytic diplococci, first described by Louis Pasteur in 1881. These lancet-shaped bacteria are surrounded by a prominent capsule, making them highly resistant to the immune system. Pneumococcus is a major cause of community-acquired pneumonia, meningitis, otitis media, sinusitis, and septicemia. It is a facultative anaerobe, non-motile, non-spore forming, and catalase-negative organism. Due to its pathogenic nature, pneumococcus-bacteria remain one of the most important human pathogens worldwide.

Pneumococcus Species

Only one species: Streptococcus pneumoniae.Multiple serotypes (>95) based on capsular polysaccharide antigen (some serotypes highly invasive).

Pneumococcus Morphology

Gram-positive cocci in pairs (diplococci), sometimes short chains.
Shape: Lancet-shaped (elongated with pointed ends).
Capsule: Prominent polysaccharide capsule, antiphagocytic, major virulence factor.
Non-motile, non-sporing.

Pneumococcus Culture Media

Blood agar: Small, dome-shaped colonies → later develop central umbilication (due to autolysis).
Hemolysis: α-hemolysis (greenish zone around colonies).
Chocolate agar: Growth enhanced.
Enrichment broth: Todd-Hewitt broth.
Growth enhanced by 5–10% CO₂ (capnophilic).

Pneumococcus Biochemical Reactions

Catalase: Negative.
Optochin sensitivity: Sensitive (key differentiating test from Viridans streptococci).
Bile solubility: Positive (lysed by bile salts).
Inulin fermentation: Positive.

Pneumococcus Resistance

Traditionally sensitive to penicillin.Penicillin resistance emerging due to altered PBP genes.Resistance also reported to macrolides (erythromycin) and tetracyclines.Multidrug-resistant strains (MDR pneumococci) are a growing problem worldwide.

Pneumococcus Antigen Structure

Capsular polysaccharide:95 serotypes; basis of Quellung reaction (capsule swelling test).
Antiphagocytic → major virulence factor.
C-substance (teichoic acid): Reacts with C-reactive protein (CRP).
Protein antigens: Pneumolysin (toxin), autolysin.

Pneumococcus Toxins & Enzymes

Pneumolysin: Cytotoxin; damages ciliated epithelium, suppresses oxidative burst of phagocytes.
Autolysin: Causes self-lysis → release of pneumolysin and inflammatory components.
IgA protease: Destroys IgA on mucosal surfaces → helps colonization.
Neuraminidase, hyaluronidase: Tissue spread.

Pneumococcus Pathogenesis

Transmission: Respiratory droplets.
Colonization: Nasopharynx (especially in children).
Spread: From colonization site → sinuses, middle ear, lungs, bloodstream, meninges.
Virulence factors: Capsule, pneumolysin, IgA protease, autolysin.
Diseases caused:
* Respiratory infections: Pneumonia (lobar), sinusitis, otitis media.
* Invasive infections: Meningitis, septicemia, bacteremia.
* Others: Endocarditis, peritonitis.

Pneumococcus Antibiotic Sensitivity

Penicillin G: DOC for sensitive strains.
Ceftriaxone / Cefotaxime: For meningitis or severe infections.
Vancomycin + Ceftriaxone: Empirical therapy for meningitis until sensitivity known.
Levofloxacin, linezolid: Alternative in resistant strains.

Pneumococcus Prevention:

Vaccination –
Pneumococcal conjugate vaccine (PCV-13, PCV-15, PCV-20) → children.
Pneumococcal polysaccharide vaccine (PPSV-23) → adults & high-risk groups.

Pneumococcus Epidemiology

Reservoir: Human nasopharynx.
Carriage: Common in children <5 years (asymptomatic carriers).
Transmission: Droplets, close contact.
High-risk groups:
Children <5 years, elderly, immunocompromised (HIV, splenectomy, hematologic malignancy).
Patients with chronic diseases (COPD, diabetes, alcoholism).

Pneumococcus Laboratory Diagnosis

Specimens: Sputum, blood, CSF, ear swab, pleural fluid.
Microscopy: Gram-positive lancet-shaped diplococci.
Capsule demonstrated by Quellung reaction (capsular swelling).
Culture: Blood agar (α-hemolysis, umbilicated colonies).
Biochemical tests: Optochin sensitivity (positive), bile solubility (positive).
Antigen detection: Capsular antigen in CSF/urine by latex agglutination.
Molecular tests: PCR for rapid diagnosis, serotyping.

Pneumococcus Treatment

Uncomplicated infections: Penicillin or amoxicillin (if sensitive).
Severe infections (meningitis, pneumonia, sepsis):
Ceftriaxone or cefotaxime ± vancomycin.
Resistant strains: Linezolid, fluoroquinolones.
Supportive treatment: Oxygen, fluids, antipyretics.
Prevention: Vaccination + prophylaxis in immunocompromised.

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