Often referred to as “liquid gold,” breast milk supports not only for children’s physical health but also for their emotional well-being. It has been linked to greater protection against infections, a lower risk of overweight and type 2 diabetes, protection from 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 carrying antibiotic resistance genes—one of the top ten global public health threats identified by the World Health Organization.
The researchers found that breast milk promotes the growth of Bifidobacterium species in the baby’s early gut microbiota. These beneficial bacteria are associated with fewer antimicrobial resistance genes and fewer harmful microorganisms. The study also revealed that exclusive breastfeeding at the beginning of life can offset the negative effects of being born by C-section and of early antibiotic exposure.
“Our findings provide scientific evidence of the importance of breastfeeding for both short- and long-term infant health,” the authors write. They emphasize the need to encourage breastfeeding as a way to protect both mother and child—and to help curb the spread of resistance genes across the population.
Offsetting the effects of cesarean delivery
Previous studies had already shown that factors such as cesarean birth, antibiotic exposure at birth, or the absence of breastfeeding can alter the establishment of the infant 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 affect the presence of microbial genes involved in antibiotic resistance. To do so, they analyzed fecal samples from 66 infants and their mothers participating in the MAMI cohort—a group followed from birth to age six to study how the infant microbiota develops over time.
The results, published in Nature Communications, show that infants breastfed for at least six months had fewer antibiotic-resistant bacteria in their gut than those fed with formula or breastfed for a shorter period.
Breastfeeding favored the presence of Bifidobacterium, which appeared to mitigate the negative effects of cesarean birth. C-sections are known to disrupt the natural transfer of maternal microbiota to the baby, altering how the infant’s microbiota is established. They also involve exposure to antibiotics early in life, which can promote the emergence of resistant bacteria.
In this study, C-section infants exclusively breastfed during the first month of life harbored fewer resistance genes than those fed with formula. In fact, their levels of antimicrobial resistance genes were comparable to those of vaginally born, breastfed infants.
“Exclusive breastfeeding not only benefits the baby in the present, but also has lasting implications 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 resistome. Nat Commun. 2025 Jul 2;16(1):6099. doi: 10.1038/s41467-025-61154-w
