Group B streptococci

Group B Strep - Baby's Big Foe

• Streptococcus agalactiae; β-hemolytic, bacitracin-resistant.
• Colonizes vagina & GIT; major risk is vertical transmission to neonate during birth.
• Neonatal Disease:
  • Early-onset (<7 days): Sepsis, pneumonia, meningitis.
  • Late-onset (>7 days): Meningitis, bacteremia.
• Screening: Universal rectovaginal culture for all pregnant women at 36-37 weeks gestation.
• Prophylaxis: Intrapartum penicillin G for positive screen or GBS risk factors (e.g., prolonged rupture of membranes >18 hrs, fever).

⭐ The CAMP test is a key identifier: GBS produces a diffusible protein (CAMP factor) that enhances the β-hemolysis of Staphylococcus aureus.

Clinical Punch - From Neonate to Nanna

• Neonates: Leading cause of early-onset sepsis & meningitis.
  • Early-onset (<7 days): Pneumonia, sepsis, meningitis. Acquired in-utero or during delivery.
  • Late-onset (7 days - 3 months): Bacteremia with meningitis is common.
• Pregnant Women:
  • Usually asymptomatic carriers (vaginal/rectal colonization).
  • Can cause chorioamnionitis, endometritis, or UTIs.
  • 📌 Universal screening via rectovaginal culture at 36-37 weeks gestation.
• Non-pregnant Adults (esp. Elderly/Comorbid):
  • Pneumonia, skin and soft tissue infections (cellulitis), bacteremia, and endocarditis.
  • Associated with diabetes mellitus, malignancy, and other immunocompromised states.

⭐ Exam Favorite: Streptococcus agalactiae (GBS) is the most common cause of meningitis in neonates <1 month old.

Lab Sleuthing - Catching the Culprit

• Specimens: Vaginal/rectal swabs (35-37 weeks gestation), blood, CSF.
• Microscopy: Gram-positive cocci in chains.
• Culture: Narrow zone of β-hemolysis on blood agar.
• Key Tests: Catalase-negative, Bacitracin-resistant.

⭐ The CAMP test is a classic identifier. GBS produces a diffusible CAMP factor that enhances the β-hemolysis of Staphylococcus aureus, creating a distinct arrowhead-shaped zone of hemolysis.

📌 Bacitracin-resistant, Beta-hemolytic, Big-time Baby-killer.

Treatment & Shielding - Penicillin's Power Play

• Primary Treatment: IV Penicillin G is the drug of choice for maternal and neonatal GBS infections. Ampicillin is an alternative.
• Penicillin Allergy:
  • Low-risk (e.g., rash): Cefazolin.
  • High-risk (anaphylaxis): Clindamycin (if susceptible) or Vancomycin.
• Intrapartum Antibiotic Prophylaxis (IAP): Essential to prevent vertical transmission. Administer IV antibiotics ≥4 hours before delivery.

⭐ Intrapartum prophylaxis is highly effective at preventing early-onset (<7 days) neonatal GBS disease but does not prevent late-onset disease or eradicate maternal colonization.

• *Risk factors: Labor <37 wks, ROM ≥18 hrs, or intrapartum fever ≥38°C.

High‑Yield Points - ⚡ Biggest Takeaways

• Group B Strep (S. agalactiae) is a leading cause of neonatal meningitis, sepsis, and pneumonia.
• Transmission is typically vertical from the mother's colonized vagina during birth.
• Universal screening for pregnant women is performed at 35-37 weeks gestation.
• Intrapartum penicillin is the standard prophylaxis for colonized mothers or those with risk factors.
• Lab diagnosis: CAMP test positive, bacitracin-resistant, and positive for hippurate hydrolysis.
• The primary virulence factor is its polysaccharide capsule, which inhibits phagocytosis.