Mothers who use breast pumps to express milk may be putting their children at risk of asthma, because they carry the wrong kind of bacteria, a new study suggests.
Researchers found milk from the devices contained higher levels of potentially harmful bugs compared to milk which came straight from the mother’s breast.
Babies may also be missing out on helpful bacteria passed directly from the mother if they drink milk which has been expressed, the study also found.
Canadian lead scientist Dr Shirin Moossavi, from the University of Manitoba, Canada, said: “Increased exposure to potential pathogens in breast milk could pose a risk of respiratory infection in the infant, potentially explaining why infants fed pumped milk are at increased risk for paediatric asthma compared to those fed exclusively at the breast.”
Britain has one of the lowest breastfeeding rates in the Western world with just 34 per cent of babies still receiving breast milk at six months of age, compared to 62 per cent in Sweden.
Breast milk is now known to contain a complex cocktail of bacteria that may be important in establishing a thriving population of friendly bugs in the stomach and guts of babies.
Disruption to the infant microbiome could leave a child vulnerable to allergies, asthma or obesity, and even cancer, some studies have suggested.
However it was unclear how bacteria entered the gut and scientists wanted to test if breast pumps could be a sources of new, and potentially harmful, bugs.
For the study, the researchers looked for bacterial genes in breast milk samples from 393 healthy mothers three to four months after giving birth.
The team found the bacterial content of milk being fed to the mothers' babies differed greatly from infant to infant.
Milk administered from breast pumps contained higher levels of potentially harmful "opportunistic pathogens" such as Stenotrophomonas and Pseudomonadaceae.
In contrast direct breastfeeding without a pump was associated with microbes typically found in the mouth, as well as greater bacterial richness and diversity.
Senior author Dr Meghan Azad, from the Children's Hospital Research Institute of Manitoba, said: “This study considerably expands our understanding of the human milk microbiota and the factors that might influence it.
“The results will inspire new research about breastfeeding and human milk, especially related to pumping.”
The new evidence suggests infant mouth microbes play an important role in determining what kind of bacteria are found in mothers' milk, said the scientists.
The research is published in the journal Cell Host & Microbe.