Indirect breastfeeding - using pumps to extract milk from the breasts - can expose babies to potential pathogens that increase the risk of asthma and other respiratory infections, a study claims.

A breast pump is a mechanical device that lactating women use to extract milk from their breasts. Many mothers use them to continue breastfeeding after they return to work. It is also used to address a range of challenges parents may encounter breast feeding.

The research, published in the journal Cell Host & Microbe, suggests that the milk microbiota is affected by bacteria both from the infant's mouth and from environmental sources such as breast pumps.

The large-scale analysis showed that using pumped milk is associated with the depletion of oral bacteria and a higher abundance of potential pathogens compared with direct breastfeeding at the breast.

Although previously considered sterile, breastmilk is now known to contain a low abundance of bacteria.

While the complexities of how maternal microbiota influence the infant microbiota are still unknown, this complex community of bacteria in breastmilk may help to establish the infant gut microbiota.

Disruptions in this process could alter the infant microbiota, causing predisposition to chronic diseases such as allergies, asthma, and obesity.

Although recent studies on human milk microbiota suggest that it might be affected by various factors, these findings have not been reproduced in large-scale studies, and the determinants of milk microbiota are still mostly unknown.

To address this gap in knowledge, researchers carried out bacterial gene sequencing on milk samples from 393 healthy mothers three to four months after giving birth.

They used this information to examine how the milk microbiota composition is affected by maternal factors, early life events, breastfeeding practices, and other milk components.

Specifically, indirect breastfeeding was associated with a higher abundance of potential opportunistic pathogens, such as Stenotrophomonas and Pseudomonadaceae.

By contrast, direct breastfeeding without a pump was associated with microbes typically found in the mouth, as well as higher overall bacterial richness and diversity.

Taken together, the findings suggest that direct breastfeeding facilitates the acquisition of oral microbiota from infants, whereas indirect breastfeeding leads to enrichment with environmental bacteria.

The researchers also observed differences in the milk microbiota depending on the infant sex.

These findings further support the idea that the milk microbiota is partially derived from the infant oral cavity, which may differ in male versus female infants.