GBS colony counts decline rapidly after penicillin prophylaxis.
Intrapartum administration of antibiotics (penicillin or ampicillin) to mothers with positive cultures for group B streptococcus (GBS) reduces the risk for early-onset disease in neonates, but the mechanism of protection is not clearly understood. Bactericidal antibiotic levels are achieved in the fetus and amniotic fluid within minutes of maternal administration, but optimal reduction of neonatal transmission takes hours.
In this prospective study, 27 women whose antepartum vaginal cultures were positive for GBS received penicillin during labor at a single hospital in New York. Vaginal samples were obtained for culture just before penicillin administration and every 2 hours thereafter for 8 hours or until delivery. Colony counts were perfor…