Besides being a source of nutrition, breast milk also plays an important role in shaping a healthy oral microbiome in babies, suggests a study.
The study, led by Queensland University of Technology (QUT), showed that the growth of some microbes was inhibited for up to 24 hours following breast milk and saliva mixing.
This slowing down was irrespective of whether the microorganism was considered to be "pathogenic" (harmful) or "commensal" (normally found) in an infant's mouth.
It could be because the interaction of neonatal saliva and breast milk releases antibacterial compounds, including hydrogen peroxide, the researchers said.
"Breast milk is high in an enzyme called xanthine oxidase which acts on two substrates, found in babies' saliva," said Emma Sweeney, from QUT's Institute of Health and Biomedical Innovation.
"The release of hydrogen peroxide from this interaction also activates the 'lactoperoxidase system' which produces additional compounds that also have antibacterial activity, and these compounds are capable of regulating the growth of microorganisms," she added, in the paper published in the journal Scientific Reports.
Sweeney noted that the composition of newborns' mouth microbiota was an important factor in health and well-being.
"Changes to these bacterial communities in newborns have important implications for infection or disease early in life," she said.
"While adult oral microbiota are stable, our studies have shown that the microbiota in the mouths of newborns is much more dynamic and seems to be altered by the mode of feeding within the first few months of life."
However, this also has significant implications for premature or sick babies who are fed via a tube.
"In these cases, the mixing of breast milk and babies' saliva does not occur and so they do not receive the benefits of the antibacterial compounds released during breastfeeding.
"Other researchers have shown that hydrogen peroxide can remain active at pH levels similar to that of a baby's stomach, so we think that this antimicrobial activity seen in the mouth may also continue within the baby's stomach and intestines," Sweeney said.