UC San Diego

Emerging studies suggest that antibiotics can disrupt the gut microbiome and alter vaccine-induced immune responses. However, the specific consequences of early-life exposure on neonatal immune development remain poorly understood. Here, we examined how two antibiotics frequently used in perinatal care, broad-spectrum ampicillin (AMP) and the extended-spectrum combination amoxicillin/clavulanate (AMOX/CLAV), administered during gestation and lactation, influence neonatal gut microbiome composition, fecal metabolome profiles, and responses to the 20-valent pneumococcal conjugate vaccine (PCV20). Maternal treatment with AMOX/CLAV, but not AMP, significantly reduced PCV-specific IgG titers at 4 and 6 weeks post-prime immunization compared to untreated controls. Exclusive exposure to AMOX/CLAV also impaired neutrophil-mediated opsonophagocytic killing, indicating reduced antibody functionality. These effects were transient, with immune parameters normalizing by 8 weeks post-prime immunization. Metabolomic and microbiome profiling revealed that maternal AMP and AMOX/CLAV differentially perturbed specific metabolite classes, including bile acids, N-acyl lipids, and indole derivatives. Key commensal taxa, including Bacteroidales and Coriobacteriales were also impacted within the gut microbiota. Together, these findings reveal a previously underappreciated maternal-offspring route of antibiotic influence that is transiently associated with neonatal vaccine responsiveness and microbiome and metabolome alterations. These results highlight maternal antibiotic exposure as a possible modifiable factor shaping early-life immunity.