Breast milk shows benefit against antibiotic resistance

Breast Milk Shows Benefit Against Antibiotic Resistance in Infants

Poinews.com – Breast milk shows benefit against antibiotic resistance genes colonising the infant gut, according to an international study led by Spain’s National Research Council (CSIC). Published in Cell Reports Medicine, the research demonstrates that babies who receive exclusive breastfeeding carry a measurably lower abundance and diversity of antimicrobial resistance genes in their intestinal microbiota during the earliest months of life. The finding positions human milk not merely as nutrition but as an active ecological agent shaping which bacterial populations thrive in a developing gut.

How Human Milk Oligosaccharides Modulate Gut Bacteria

At the centre of the mechanism are human milk oligosaccharides (HMOs), complex sugar molecules present in high concentration in breast milk. Infants cannot digest HMOs directly; instead, the sugars pass intact into the lower intestine where they feed select beneficial bacterial species. By preferentially nourishing those microbes, HMOs reshape the competitive landscape of the gut ecosystem and can suppress populations that harbour specific resistance genes.

“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,” explains M. Carmen Collado, a CSIC researcher at the Institute of Agrochemistry and Food Technology (IATA).

Collado and her team stress that the first months after birth constitute a narrow developmental window. During this period the intestinal microbiome is still assembling, and external inputs—feeding method, mode of delivery, early antibiotic exposure—can imprint lasting structural changes on the resistome, the collective inventory of antimicrobial resistance genes residing in gut bacteria.

Study Design and Cross-Country Validation

The primary cohort comprised faecal samples from 57 one-month-old infants in Valencia, Spain, paired with corresponding milk samples from their mothers. Researchers sequenced both datasets to map which resistance genes were present and how their diversity correlated with feeding history. To confirm the findings beyond a single population, the team subsequently validated the results using data from 199 breastfed babies in the Netherlands, reinforcing the association between exclusive breastfeeding and a leaner resistome.

Delivery mode emerged as an additional variable. Babies born by caesarean section displayed a different resistome profile compared with those delivered vaginally, underscoring that multiple early-life factors interact to determine the trajectory of gut microbial composition.

“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 ivery or feeding, can leave a lasting imprint,” notes Anna Samarra, a researcher trained at IATA-CSIC and now a postdoctoral fellow at the University of California, San Diego.

Frequently Asked Questions

Does this study prove that breastfeeding prevents antibiotic resistance? It demonstrates a statistical association: exclusively breastfed infants carried fewer and less diverse resistance genes in their gut microbiota. It does not establish a direct causal pathway, but the biological plausibility of HMO-mediated microbial selection supports the link.

Can formula-fed babies receive similar benefits? Current evidence does not show that standard infant formula replicates the ecological effect of HMOs. Some fortified formulas include added oligosaccharides, but their impact on the resistome has not been confirmed at the scale of this study.

How long after birth is the critical window? The study focused on one-month-old infants. Researchers describe the first several months as the period of greatest susceptibility, after which the microbiome stabilises and becomes harder to reshape through dietary intervention alone.

What practical steps can parents take? Where medically appropriate, exclusive breastfeeding for the earliest months aligns with the study’s findings. Parents should discuss feeding choices with paediatricians and avoid unnecessary early antibiotic courses, which can independently alter gut microbial balance.