Often referred to as ‘liquid gold’, Breast milk not only supports children’s physical health, but also their emotional well-being. It has been linked to better protection against infections, a lower risk of obesity and type 2 diabetes, protection against sudden infant death syndrome and improved cognitive development.
Now, to this long list of benefits, an international study led by the Institute of Agrochemistry and Food Technology (IATA-CSIC, Spain) adds a new one: Exclusive breastfeeding during the first month of life also acts as a protective shield against bacteria that carry antibiotic resistance genes– one of the top ten global threats to public health, identified by the World Health Organization.
The researchers discovered this Breast milk promotes growth Bifidobacterium species in the infant’s early gut microbiota. These beneficial bacteria are associated with fewer antimicrobial resistance genes and fewer harmful microorganisms. This was also evident from the research Exclusive breastfeeding early in life can offset its negative effects being born via caesarean section and from early exposure to antibiotics.
“Our findings provide scientific evidence of the importance of breastfeeding for infant health in the short and long term,” the authors write. They emphasize the need to encourage breastfeeding as a way to protect both mother and child – and to prevent the spread of resistance genes in the population.
Compensating for the consequences of a caesarean section
Previous studies had already shown that factors such as caesarean section, exposure to antibiotics at birth or lack of breastfeeding can alter the establishment of the child’s microbiota, potentially increasing the risk of developing conditions such as allergies, asthma or obesity.
In this new study IATA CSIC researchers focused on how these factors influence the presence of microbial genes involved in antibiotic resistance. To do this, they analyzed fecal samples from 66 infants and their mothers who participated MAMI cohort–followed a group from birth to age six to study how babies’ microbiota develop over time.
The results, published in Nature communicationshow that infants who were breastfed for at least six months had fewer antibiotic-resistant bacteria in their intestines than infants who were formula-fed or breastfed for a shorter period.
Breastfeeding promoted the presence of Bifidobacteriumwhich seemed to alleviate the negative effects of a caesarean section. Cesarean sections are known to disrupt the natural transfer of microbiota from the mother to the baby, altering the way the baby’s microbiota is built. They also involve exposure to antibiotics at a young age, which can promote the emergence of resistant bacteria.
In this study, cesarean section infants who were exclusively breastfed during the first month of life had fewer resistance genes than bottle-fed infants. In fact, their levels of antimicrobial resistance genes were comparable to those of vaginally born breastfed babies.
“Exclusive breastfeeding not only benefits the baby in the present, but also has lasting consequences for long-term gut health.” explains Anna Samarra, researcher at IATA-CSIC and first author of the study.
Reference
Samarra A, Alcañiz AJ, Martínez-Costa C, et al. Breastfeeding and early Bifidobacterium-driven microbial colonization shape the infant gut. Nat Commun. 2 Jul 2025;16(1):6099. doi: 10.1038/s41467-025-61154-w
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