Breast milk components link to fewer antibiotic-resistance genes in infant gut

Fifty-seven one-month-old babies in Valencia provided stool samples for a study that linked exclusive breastfeeding to fewer antibiotic-resistance genes in the infant gut, according to a report by Euronews on research led by Spain’s National Research Council (CSIC). The team also analysed milk samples from the babies’ mothers, and the findings were published in Cell Reports Medicine.

The paper sits at an awkward intersection of two public-health realities: antibiotic resistance is treated as a looming systems crisis, while early-life feeding is one of the few levers that can be changed without inventing a new drug. The researchers focus on human milk oligosaccharides (HMOs), naturally occurring molecules in breast milk that infants largely do not digest themselves. Instead, HMOs feed selected microbes, shaping which bacteria thrive in the intestine during what the authors describe as a critical window when the microbiota is being established.

In the Valencia cohort, exclusive breastfeeding was associated with a lower abundance and lower diversity of antimicrobial resistance genes in the babies’ intestines. The study also reports that some HMOs correlate with a lower presence of specific resistance genes, suggesting that milk composition may influence which bacteria — and which genetic toolkits — gain a foothold. The mechanism proposed is ecological rather than pharmaceutical: HMOs promote microorganisms that can use them, and that shift in the microbial community may limit the spread of bacteria carrying certain resistance genes.

The researchers also examined delivery mode, reporting differences in the diversity of resistance genes between babies born by caesarean section and those delivered vaginally. But the association between exclusive breastfeeding and fewer resistance genes held regardless of delivery mode, according to Euronews’ summary of the paper. To check that the pattern was not unique to one city and one sampling protocol, the team validated results using data from another 199 breastfed babies in the Netherlands.

The study’s appeal is that it reframes “superbugs” partly as a question of early microbial selection pressures, not only hospital prescribing habits. It also hints at why broad calls to fight resistance can end up defaulting to expensive late-stage interventions: it is easier to fund new antibiotics than to build systems that support breastfeeding in the first months of life, or to track resistance genes in healthy populations before infections appear.

The dataset begins with infants just one month old, and the outcome is genetic potential for resistance rather than clinical infection. But the paper’s core observation is concrete: in the Valencia samples, babies fed only breast milk carried fewer antibiotic-resistance genes than peers who were not exclusively breastfed.