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: commonly and asymptomatically colonizes the maternal genital and lower gastrointestinal tract (~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 (first week, typically first 24–48 hours) — sepsis, pneumonia, or meningitis, acquired from the maternal genital tract; late-onset neonatal disease (1 week to 3 months) — predominantly bacteraemia and meningitis; maternal disease — postpartum endometritis, chorioamnionitis, UTI, and post-caesarean wound infection.
Laboratory identification: beta-haemolytic colonies on blood agar; CAMP test positive; bacitracin-resistant (unlike Group A Streptococcus); hydrolyses hippurate; possesses the Lancefield Group B carbohydrate antigen.
Prevention: universal antenatal screening (vaginal/rectal swab culture at 35–37 weeks) for maternal GBS colonization, with intrapartum antibiotic prophylaxis (IV penicillin/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).