Randomized, Placebo-Controlled Trial of Transplacental Antibiotic Prophylaxis of Neonatal Group B Streptococcal Colonization and Bacteremia in Rabbits

Objective: We evaluated the effect of maternal administration of ampicillin/sulbactam on colonization and bacteremia in newborn rabbits after intracervical inoculation of mothers with group B streptococci (GBS). Methods: New Zealand white rabbits on day 30 of a 31-day gestation were inoculated intracervically with 10(4)−10(5) colony forming units (cfu) GBS. Two hours after inoculation mothers received ampicillin/sulbactam (50 mg/kg) or saline (control) intramuscularly as a single dose, in a randomized double-blinded manner. We induced labor 4 h later with intramuscular oxytocin. At delivery, cultures for GBS were taken from neonatal oropharynx. Thereafter, cultures were taken from neonatal oropharynx and anorectum daily and from neonatal heart at death or after 96 h. Sample size analysis showed a need for 17 pups in each group. Results: In the control group, induction failed in one animal that was excluded from analysis. At birth, 0 of 39 pups of treated does had positive oropharyngeal cultures compared to 26 of 27 (96%) pups of saline-treated does (P < 0.0001). Pups treated with antibiotic in utero were also significantly less likely to have positive oropharyngeal cultures at 24, 48, and 72 h after birth compared to controls (24 h, 0% vs. 100%, P < 0.0001; 48 h, 8% vs. 100%, P < 0.0001; 72 h, 16% vs. 100%, P < 0.0001). Treated pups were significantly less likely to have positive anorectal cultures at 24, 48, and 72 h after birth compared to control animals (24 h, 0% vs. 100%, P < 0.0001; 48 h, 0% vs. 95%, P < 0.0001; 72 h, 0% vs. 92%, P < 0.0001). Treated pups were significantly less likely to have positive heart cultures at 72 h after birth compared to controls (11% vs. 92%, P < 0.0002). Cumulative neonatal survival was higher in treated pups compared to controls at 72 and 96 h after birth (72 h, 32% vs. 0%, P = 0.0003; 96 h, 26% vs. 0%, P = 0.015). Conclusions: Single dose transplacental prophylaxis given 4 h before delivery resulted in decreased neonatal GBS colonization and bacteremia and improved neonatal survival in rabbits.