Question
Group B streptococci
Answer
Group B Streptococcus (GBS, Streptococcus agalactiae) is a Gram-positive, beta-haemolytic coccus, an important cause of neonatal sepsis and meningitis, and also a cause of maternal peripartum/postpartum infection.
Colonization and transmission: GBS commonly and asymptomatically colonizes the maternal genital and lower gastrointestinal tract (found in up to ~25–30% of pregnant women); transmission to the neonate occurs primarily during passage through the birth canal, or by ascending infection after prolonged rupture of membranes.
Clinical disease:
- Early-onset neonatal disease (within the first week of life, typically first 24–48 hours) — acquired from the maternal genital tract during labour/delivery; presents as sepsis, pneumonia, or meningitis, and can progress rapidly.
- Late-onset neonatal disease (1 week to 3 months) — acquisition may be from the mother or environmental/nosocomial sources; presents predominantly with bacteraemia and meningitis.
- Maternal disease — postpartum endometritis, chorioamnionitis, urinary tract infection, and wound infection following caesarean section.
Laboratory identification: beta-haemolytic colonies on blood agar; CAMP test positive (enhanced haemolysis in an arrowhead pattern adjacent to a Staphylococcus aureus streak, exploiting the synergistic action of CAMP factor with staphylococcal beta-toxin); bacitracin-resistant (unlike Group A Streptococcus, which is bacitracin-sensitive) — an important distinguishing feature in routine identification; hydrolyses hippurate; possesses the Lancefield Group B carbohydrate antigen.
Prevention: universal antenatal screening (vaginal/rectal swab culture at 35–37 weeks of gestation) for maternal GBS colonization, with intrapartum antibiotic prophylaxis (typically IV penicillin or ampicillin during labour) for colonized mothers or those with risk factors (previous GBS-affected infant, GBS bacteriuria in current pregnancy, preterm labour, prolonged rupture of membranes, intrapartum fever) — the mainstay strategy for preventing early-onset neonatal GBS disease.