A new international study led by Spain's National Research Council (CSIC) suggests that breastfeeding may help reduce the presence of antibiotic-resistance genes in babies' gut microbiota. The research, published in Cell Reports Medicine, offers a fresh angle in the fight against antimicrobial resistance, a growing public health concern across Europe and beyond.
The team, based at the Institute of Agrochemistry and Food Technology (IATA) in Valencia, analysed faecal samples from 57 one-month-old infants in the city, alongside milk samples from their mothers. They then validated their findings using data from 199 breastfed babies in the Netherlands. The results show that exclusive breastfeeding is linked to a lower abundance and diversity of antimicrobial resistance genes in the infant gut.
“Promoting breastfeeding appears to be an effective strategy for reducing antimicrobial resistance genes present in intestinal bacterial communities during a critical stage in the development of the microbiota,” said M. Carmen Collado, a CSIC researcher at IATA and lead author of the study.
How breast milk shapes the infant resistome
The key appears to lie in human milk oligosaccharides (HMOs), complex carbohydrates that are abundant in breast milk. Babies cannot digest HMOs directly, but these molecules serve as food for beneficial gut bacteria, helping to establish a balanced microbial community. The researchers found that certain HMOs are associated with a lower presence of genes that confer resistance to antibiotics.
“HMOs act as ecological modulators of the gut microbiota: they promote the growth of microorganisms capable of using them and may limit the spread of bacteria carrying specific resistance genes,” Collado explained.
The study also highlights the role of delivery mode. Infants born by caesarean section showed different diversity of resistance genes compared with those born vaginally, while exclusive breastfeeding was consistently associated with a reduced load of these genes. This suggests that both feeding and birth method leave a lasting imprint on the infant's gut ecosystem.
“The first months of life represent a critical window in which the gut microbiota is being established and in which different environmental factors, such as mode of delivery or feeding, can leave a lasting imprint,” said Anna Samarra, a researcher trained at IATA-CSIC and now a postdoctoral researcher at the University of California, San Diego.
The findings add to a growing body of evidence that early-life interventions can influence long-term health. Antimicrobial resistance is a major global threat, and the intestinal resistome—the collection of resistance genes in gut bacteria—is a key reservoir. By reducing the abundance of these genes in infancy, breastfeeding may help curb the spread of resistant bacteria later in life.
The study's authors stress that their work is observational and that more research is needed to confirm the causal mechanisms. However, the results reinforce existing public health recommendations that promote breastfeeding as a cornerstone of infant health. In the European context, where breastfeeding rates vary widely between member states, the findings could inform policy discussions on maternal and child health.
For parents and clinicians, the takeaway is clear: supporting breastfeeding is not only beneficial for nutrition and immunity but may also play a role in the broader fight against antibiotic resistance. As Europe grapples with rising antimicrobial resistance, this study offers a simple, low-cost preventive measure that could have significant long-term benefits.
