Researchers from Spain have managed to identify all of the bacteria found in breast milk. The finding, published in the American Journal of Clinical Nutrition, reveals that there is much more microbial diversity in milk than expected, with there being more than 700 different types of bacteria.

The breast milk newborns drink regulates their development of bacterial flora. The biological role of the bacteria found in the milk is still not quite understood, yet it is crucial. A previous study published in the journal Current Nutrition & Food Science found that breast milk contains substantial amounts of friendly bacteria which helps babies absorb nutrients and develop the immune system.

DNA sequencing helped the Spanish researchers identify the group of bacteria in milk, known as microbiome. The microbial richness of breast milk is determined by a number of pre and postnatal factors.

The first type of milk a woman produces during pregnancy and in the early days of breastfeeding is called colostrum. This easy to digest milk is very nutritious and the perfect first food for a newborn. The scientists examined this type of milk and found that there are more than 700 different types of bacteria in it.

According to the coauthors of the study, María Carmen Collado and Alex Mira:

“This is one of the first studies to document such diversity using the pyrosequencing technique (a large scale DNA sequencing determination technique) on colostrum samples on the one hand, and breast milk on the other, the latter being collected after one and six months of breastfeeding.”

Analysis of colostrum samples revealed that the most common types of bacteria were Streptococcus, Lactococcus, Leuconostoc, Weissella and Staphylococcus. Samples of breast milk produced between the first and sixth month of pregnancy were also analyzed, the most common bacteria was Prevotella, Leptotrichia and Veillonella.

The authors added: “We are not yet able to determine if these bacteria colonise the mouth of the baby or whether oral bacteria of the breast-fed baby enter the breast milk and thus change its composition,”

The breast milk from mothers who were either overweight or obese was found to have less bacteria than breast milk from mothers who were a healthy weight. They also found that the milk from mothers who gave birth through a planned Caesarean section rather than vaginal birth was less rich and had fewer microorganisms. This could mean that the hormonal state of the mother can influence the composition of breast milk.

The authors said: “The lack of signals of physiological stress, as well as hormonal signals specific to labour, could influence the microbial composition and diversity of breast milk.”

The ingestion of breast milk is the first time a baby has contact with microorganisms that will end up in it’s digestive system. The researchers are currently trying to find out whether or not the role of the bacteria is either immune or metabolic.

The authors conclude:

“If the breast milk bacteria discovered in this study were important for the development of the immune system, its addition to infant formula could decrease the risk of allergies, asthma and autoimmune diseases.”

Written by Joseph Nordqvist