Study Reveals Breast Milk’s Role in Combating Infant Antibiotic Resistance

International research led by Spain’s National Research Council (CSIC) indicates that breast milk may help reduce antibiotic resistance genes in infants’ guts, examining how human milk components influence early gut bacteria.

Published in Cell Reports Medicine, the study reveals that exclusive breastfeeding correlates with reduced abundance and diversity of antimicrobial resistance genes in infants’ intestines.

“Promoting breastfeeding serves as an effective strategy for lowering antimicrobial resistance genes in intestinal bacterial communities during a critical stage of microbiota development,” explains M. Carmen Collado, a CSIC researcher at the Institute of Agrochemistry and Food Technology (IATA).

How Does Breast Milk Influence Antibiotic Resistance?

A key factor is human milk oligosaccharides (HMOs), natural molecules in breast milk that infants do not digest directly but which nourish beneficial gut bacteria and help maintain a balanced microbiota.

The researchers found that some of these components are associated with a lower presence of specific antibiotic resistance genes.

“HMOs act as ecological modulators of the gut microbiota: they promote the growth of microorganisms that utilize them and may limit the spread of bacteria carrying specific resistance genes,” says Collado.

To reach these conclusions, researchers analyzed fecal samples from 57 one-month-old babies in Valencia alongside milk samples from their mothers, later validating the results with data from 199 breastfed babies in the Netherlands.

Mode of Delivery Also Plays a Role

The study notes that both the mode of delivery and feeding are decisive factors in the composition of the intestinal resistome—the collection of antimicrobial resistance genes present in gut bacteria.

The researchers found differences in the diversity of these genes between babies born via caesarean section and those born vaginally, while exclusive breastfeeding was linked to a lower abundance and diversity of resistance genes.

“The first months of life represent a critical window in which the gut microbiota is established, and environmental factors such as delivery method or feeding can leave a lasting imprint,” explains Anna Samarra, a researcher trained at IATA-CSIC and now a postdoctoral researcher at the University of California, San Diego.

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