Makindo Medical Notes

Related Subjects: |Streptococcus Pneumoniae (Pneumococcus) |Streptococcus pyogenes Group A |Streptococcus viridans |Streptococcus milleri |Streptococcus agalactiae Group B |Microbiology and Assessment of Streptococcus

Streptococcus is a genus of Gram-positive bacteria characterised by their spherical shape (cocci) and tendency to form chains or pairs. They are facultative anaerobes and catalase-negative, distinguishing them from Staphylococcus species.

📖 Classification

• Haemolytic Properties on Blood Agar
  • 🟢 Alpha-haemolytic: Partial haemolysis, greenish discoloration. Examples: S. pneumoniae, Viridans streptococci.
  • 🔴 Beta-haemolytic: Complete haemolysis, clear zone. Classified further into Lancefield groups (A, B, C, G, etc).
  • ⚪ Gamma-haemolytic: Non-haemolytic; no change on agar.
• Lancefield Grouping (Cell Wall Antigens)
  • Group A: S. pyogenes
  • Group B: S. agalactiae
  • Groups C & G: Various zoonotic/human pathogens
  • Group D: Enterococcus spp. (formerly included here)

🧪 Streptococcus pyogenes (Group A)

• Morphology: Gram-positive cocci in chains.
• Haemolysis: Beta-haemolytic.
• Virulence Factors:
  • M protein – anti-phagocytic.
  • Streptolysins O & S – exotoxins causing haemolysis.
  • Pyrogenic exotoxins – superantigens → scarlet fever, TSS.
• Diseases:
  • Suppurative: Pharyngitis, impetigo, cellulitis, erysipelas.
  • Invasive: Necrotising fasciitis, streptococcal TSS.
  • Post-infectious: Rheumatic fever, acute glomerulonephritis.

🧪 Streptococcus agalactiae (Group B)

• Morphology: Gram-positive cocci in chains.
• Haemolysis: Beta-haemolytic (narrow zone).
• Virulence Factors:
  • Capsule – resists phagocytosis.
  • Beta-haemolysin/cytolysin – tissue injury.
• Diseases:
  • Neonates: Early-onset sepsis, pneumonia, meningitis; late-onset meningitis/sepsis.
  • Adults: UTI, skin/soft tissue infections.

🧪 Streptococcus pneumoniae

• Morphology: Gram-positive, lancet-shaped diplococci.
• Haemolysis: Alpha-haemolytic.
• Virulence Factors:
  • Polysaccharide capsule – major determinant (90+ serotypes).
  • Pneumolysin – damages host cells, activates complement.
• Diseases:
  • Respiratory: CAP, otitis media, sinusitis.
  • Invasive: Meningitis, bacteraemia.

🧪 Viridans Group Streptococci

• Alpha or non-haemolytic, heterogeneous group.
• Normal oral/GI flora.
• Diseases:
  • Dental caries (S. mutans).
  • Subacute bacterial endocarditis (esp. damaged valves).

🧪 Enterococcus spp. (Group D)

• Morphology: Gram-positive cocci in pairs/short chains.
• Haemolysis: Variable (α, β, or none).
• Species: E. faecalis, E. faecium.
• Diseases:
  • Nosocomial infections: UTI, bacteraemia, endocarditis.
  • Resistance: Vancomycin-resistant enterococci (VRE).

🔎 Laboratory Identification

• Gram stain → Gram-positive cocci in chains/pairs.
• Culture on blood agar → haemolysis patterns.
• Catalase test → negative.
• Bacitracin sensitivity → Group A is sensitive.
• CAMP test → positive for GBS.
• Optochin sensitivity & bile solubility → S. pneumoniae positive.
• PYR test → positive for GAS.

🩺 Clinical Assessment

• Pharyngitis: Sudden sore throat, fever, headache; no cough/coryza.
• Skin/Soft Tissue: Red, swollen, painful; necrotising fasciitis possible.
• Systemic: High fever, chills, shock in severe cases.

👨‍⚕️ Physical Examination

• Pharynx: Red tonsils, ± exudate, palatal petechiae.
• Lymph nodes: Tender cervical lymphadenopathy.
• Skin: Erythema, swelling, bullae, necrosis.
• Vitals: Fever, tachycardia, hypotension.

🧪 Specimen Collection

• Throat swab (pharyngitis).
• Skin swab/biopsy (lesions).
• Blood cultures (sepsis).
• CSF (suspected meningitis).

⚗️ Diagnostic Tests

• Rapid antigen detection tests (RADTs) for GAS.
• Culture on blood agar → haemolysis, colony ID.
• Serology: ASO titres, anti-DNase B.
• Molecular: PCR, 16S rRNA sequencing (epidemiology/complex cases).

💊 Antimicrobial Therapy

• Group A: Penicillin V/amoxicillin. If allergy → cephalosporins, macrolides, clindamycin.
• Group B: Penicillin G (IV); intrapartum prophylaxis in carriers/high-risk pregnancies.
• S. pneumoniae: High-dose amoxicillin; resistant strains → cephalosporins, fluoroquinolones.
• Enterococcus: Ampicillin or vancomycin ± gentamicin. VRE → linezolid, daptomycin.

🩹 Supportive Care

• Analgesics, antipyretics.
• Hydration and rest.

🛡️ Prevention

• Hand hygiene reduces spread.
• Pneumococcal vaccines (PCV13, PPSV23) for children, elderly, high-risk groups.
• GBS screening in pregnancy (35–37 wks) with intrapartum prophylaxis if positive/risk factors.

⚠️ Complications

• Rheumatic fever: Autoimmune; heart, joints, skin, brain.
• Acute glomerulonephritis: Immune-mediated kidney inflammation → haematuria, proteinuria, hypertension.
• Invasive streptococcal disease: Necrotising fasciitis, TSS → needs surgery + ICU care.

📊 Prognosis

• Prompt treatment → full recovery in most cases.
• Delayed/inadequate therapy → ↑ complications and mortality.

Disclaimer: Educational purposes only. Not a substitute for medical advice — always consult guidelines and infectious disease specialists for patient care.