Streptococci and Enterococci

Strep/Entero Basics - Cocci Command Central

• Gram-positive cocci, typically in chains or pairs.
• Catalase-negative (differentiates from Staphylococci).
• Classification based on:
  • Hemolysis on blood agar:
    • α-hemolysis (partial, green; e.g., S. pneumoniae, Viridans streptococci)
    • β-hemolysis (complete; e.g., S. pyogenes, S. agalactiae)
    • γ-hemolysis (none; e.g., Enterococcus spp., Group D Streptococci)
  • Lancefield grouping (A-W): Based on C-carbohydrate antigen in cell wall.

⭐ Lancefield classification, developed by Rebecca Lancefield, is based on the C-carbohydrate (cell wall polysaccharide) antigen for most groups.

• Enterococci: Formerly Group D streptococci, now separate genus. PYR-positive, grow in 6.5% NaCl & bile esculin agar. 📌 Enterococci Endure harsh conditions (NaCl, bile).

Group A Strep - Pyogenes PowerPlay

• Virulence: M protein (key!), Streptolysins O/S, Hyaluronidase, Streptokinase, DNAses.
• Suppurative Diseases:
  • Pharyngitis, Impetigo, Erysipelas, Cellulitis, Scarlet fever, Necrotizing fasciitis, Streptococcal Toxic Shock Syndrome (STSS).
  • 📌 Mnemonic: Pharyngitis, Skin infections, Scarlet fever, Necrotizing fasciitis, Toxic Shock (PSSNT).
• Non-Suppurative Sequelae:
  • Rheumatic Fever (RF), Post-Streptococcal Glomerulonephritis (PSGN).
• Diagnosis: Throat culture, Rapid Antigen Detection Test (RADT); ASO titre (↑ for RF/PSGN).
• Treatment: Penicillin (DOC).

⭐ M protein is the major virulence factor of S. pyogenes, inhibiting phagocytosis and implicated in rheumatic heart disease.

Group B Strep & Co. - Beta Brigade

• Streptococcus agalactiae (GBS): Beta-hemolytic, bacitracin-resistant.
  • Key cause: Neonatal sepsis, pneumonia, meningitis. 📌 'Baby' for GBS neonates.
  • Maternal screening: 36-37 weeks gestation.
  • Intrapartum Antibiotic Prophylaxis (IAP) for: previous GBS neonate, GBS bacteriuria, positive screen, or unknown GBS with risk factors (fever ≥38°C, ROM ≥18h, preterm <37w).
  • Lab: Hippurate hydrolysis (+).

  ⭐ Streptococcus agalactiae (GBS) is CAMP test positive, showing synergistic hemolysis with S. aureus.

• Other Beta-hemolytic Strep (e.g., Groups C, G): Can cause pharyngitis, skin infections.

Pneumo & Viridans - Alpha Avengers

• Alpha-hemolytic streptococci, crucial distinctions.

• S. pneumoniae (Pneumococcus)

  • Gram-positive, lancet-shaped diplococci.
  • Polysaccharide capsule (virulence); Quellung reaction positive.
  • 📌 MOPS: Meningitis, Otitis media, Pneumonia (rust-colored sputum), Sinusitis.
  • Optochin-sensitive, Bile soluble.

• Viridans Streptococci

  • Normal flora (oral, GIT). S. mutans (dental caries), S. sanguinis (SBE).
  • 📌 Viridans: MOUTH flora, cause Subacute Bacterial Endocarditis (SBE) on DAMAGED valves.
  • Optochin-resistant, Bile insoluble.

⭐ Streptococcus pneumoniae is optochin-sensitive and bile soluble, key for differentiating from Viridans streptococci (optochin-resistant, bile insoluble).

Enterococci - Gut Guardians Gone Rogue

• Formerly Group D Strep; normal gut/GU flora.
• Characteristics:
  • Grow in 6.5% NaCl.
  • Bile esculin positive (blackens agar).
  • PYR positive.
• Species: E. faecalis (common), E. faecium (↑resistance).
• Infections:
  • UTIs, endocarditis (esp. post-GIT/GU surgery).
  • Intra-abdominal, biliary tract infections.
  • 📌 Enterococci hit you in your UTIs, Biliary tract, and Abdomen.
• Resistance:
  • Intrinsic: Cephalosporins, Aminoglycosides (low-level).
  • Acquired: Vancomycin (VRE) is a major threat.

⭐ Enterococci (e.g., E. faecalis, E. faecium) are notorious for high-level antibiotic resistance, including Vancomycin (VRE).

High‑Yield Points - ⚡ Biggest Takeaways

• S. pneumoniae: Lancet-shaped diplococci, optochin-sensitive, causes lobar pneumonia, meningitis.
• S. pyogenes (GAS): Bacitracin-sensitive, causes pharyngitis, rheumatic fever, PSGN.
• S. agalactiae (GBS): CAMP test positive, causes neonatal meningitis and sepsis.
• Viridans streptococci: Optochin-resistant, cause dental caries (S. mutans) and SBE.
• Enterococci: Grow in 6.5% NaCl, bile esculin positive; cause UTIs, endocarditis. VRE is a major concern.
• S. bovis/gallolyticus complex: Associated with endocarditis and colon cancer.