Antimicrobial Susceptibility Profiles Among Neonatal Early-onset Sepsis Pathogens

Pediatr Infect Dis J. 2022 Mar 1;41(3):263-271. doi: 10.1097/INF.0000000000003380.


Background: Empiric administration of ampicillin and gentamicin is recommended for newborns at risk of early-onset sepsis (EOS). There are limited data on antimicrobial susceptibility of all EOS pathogens.

Methods: Retrospective review of antimicrobial susceptibility data from a prospective EOS surveillance study of infants born ≥22 weeks' gestation and cared for in Neonatal Research Network centers April 2015-March 2017. Nonsusceptible was defined as intermediate or resistant on final result.

Results: We identified 239 pathogens (235 bacteria, 4 fungi) in 235 EOS cases among 217,480 live-born infants. Antimicrobial susceptibility data were available for 189/239 (79.1%) isolates. Among 81 Gram-positive isolates with ampicillin and gentamicin susceptibility data, all were susceptible in vitro to either ampicillin or gentamicin. Among Gram-negative isolates with ampicillin and gentamicin susceptibility data, 72/94 (76.6%) isolates were nonsusceptible to ampicillin, 8/94 (8.5%) were nonsusceptible to gentamicin, and 7/96 (7.3%) isolates were nonsusceptible to both. Five percent or less of tested Gram-negative isolates were nonsusceptible to each of third or fourth generation cephalosporins, piperacillin-tazobactam, and carbapenems. Overall, we estimated that 8% of EOS cases were caused by isolates nonsusceptible to both ampicillin and gentamicin; these were most likely to occur among preterm, very-low birth weight infants.

Conclusions: The vast majority of contemporary EOS pathogens are susceptible to the combination of ampicillin and gentamicin. Clinicians may consider the addition of broader-spectrum therapy among newborns at highest risk of EOS, but we caution that neither the substitution nor the addition of 1 single antimicrobial agent is likely to provide adequate empiric therapy in all cases.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Ampicillin
  • Anti-Bacterial Agents / pharmacology
  • Anti-Bacterial Agents / therapeutic use
  • Anti-Infective Agents / pharmacology
  • Anti-Infective Agents / therapeutic use*
  • Bacteria / drug effects*
  • Bacteria / isolation & purification
  • Gentamicins
  • Gestational Age
  • Humans
  • Infant, Newborn
  • Microbial Sensitivity Tests*
  • Neonatal Sepsis / drug therapy*
  • Neonatal Sepsis / epidemiology
  • Neonatal Sepsis / microbiology
  • Prospective Studies
  • Retrospective Studies


  • Anti-Bacterial Agents
  • Anti-Infective Agents
  • Gentamicins
  • Ampicillin

Grant support