Breastmilk contains many prebiotics to support the growth of beneficial bacteria in the infant’s gut.  It also contains bacteria that seed the infant’s gut.  Previous research has shown that the bacteria in breast milk do indeed take hold and colonize the gut, and so it is imperative to infant microbiome development.  An article published last week sought to discover if the breastmilk microbiome changes depending on mode of delivery, especially since we have seen that C-section infant’s have much different microbiomes than their vaginally delivered counterparts.  The scientists published their results in the journal Microbiome.

The scientists tested the breastmilk of 39 Canadian women.  Despite various backgrounds, each woman’s milk was dominated by Staphylococcus, Enterobacteriaceae, and Pseudomonas.  Moreover, there were not major differences in the breast milk microbiomes between modes of delivery, showing that it is not effected by C-section of vaginal birth.  In addition, the gender of the baby did not change the microbiome either.  Interestingly, the microbiomes were very different between mothers, meaning that babies are being exposed to highly diverse bacteria from milk.  In one case 80% of the bacteria were staphylococci, and in another case more than 50% was Pseudomonas.

There is little evidence that shows how differences in breast milk microbiomes are affecting children.  That said, we know the microbiome is critical to immune system development, and therefore it reasons that these differences may be important.  In any event, it is useful to see that mode of delivery itself is unlikely to change the breastmilk microbiome.

Bacteria from infants’ microbiome metabolize breast milk differently.

Human milk oligosaccharides (HMOs) are a diverse group of carbohydrates found in breastmilk.  Because the HMOs can’t be used by the infant directly for energy, scientists believe their purpose is to stimulate the development of a healthy gut microbiome.  During the first year of life, an infant’s gut is dominated by Bifidobacteria, in particular B. infantis, and B. bifidum.  In a recent publication scientists measured the difference in HMO utilization between these bugs, and discovered they have very different and important strategies for HMO utilization. The results were published in Nature Scientific Reports.

The scientists first isolated multiple strains of each species, B. infantis and B. bifidum, from the feces of newborn infants.  They then attempted to culture each strain alone in a mixture of HMOs from breastmilk, as well as the individual HMOs alone.  They learned that the each B. infantum strain could grow on pooled HMOs, but interestingly some of the B. bifidum strains could not grow alone on HMOs.  When the bacteria were cultured with mucins (containing sialic acid or fucose, as previously discussed on this blog) none of the B. infantis could grow, whereas most of the B. bifidum could.  This implies that B. infantis alone cannot utilize fucose or sialic acid, but rather needs the help of other bugs to break these down to utilize them.  After, the scientists looked at the regulation of different genes during the culturing experiments.  From these results they determined that B. infantum transports the HMOs inside the cell before breaking them down for energy.  B. bifidum, on the other hand, breaks the oligosaccharides down extracellularly before taking up smaller, simpler sugars. 

All together we see that there is a complex assemblage of bugs in the guts of infants that all rely on one another for energy and metabolism.  The breastmilk cocktail of HMOs itself is so complicated that it almost necessitates the interdependent communities to grow.  Overall, this creates a robust and resilient microbiome that prevents pathogens from taking hold and protects the infant during his or her most vulnerable years.

Infants’ saliva may react with breast milk to modulate their microbiomes

Breastmilk is critically important to developing a healthy infant gut microbiome.  The combination of oligosaccharides found in breastmilk are not found in any other individual food, and are intended to cultivate healthy bacteria in the gut.  Besides breast milk, really the only other fluid an infant consumes is his or her own saliva, but thus far not much is known about the role this saliva plays in culturing the proper microbiota.  A team of researchers from Australia recently studied how a mother’s breastmilk directly interacts with her infant’s saliva.  They discovered that when combined, saliva and breast milk produce specific molecules that inhibit the growth of some bacteria, but support the growth of others. They published their results in the journal PLoS ONE.

The researchers measured the molecular components of saliva in 77 adults and 60 infants.  They noticed some stark differences between the two types of saliva, including markedly higher levels of salivary hypoxanthine and xanthine.  Hypoxanthine and xanthine are both substrates for a protein called xanthine oxidase (XO), which reacts with them to form hydrogen peroxide (H2O2).  One of the places XO is predominantly found is in human breast milk, which led the researchers to hypothesize that xanthine and hypoxanthine in infant saliva reacts with XO in breastmilk to form H2O2.  Hydrogen peroxide is a reactive oxygen species (ROS) that can kill bacteria.  The scientists believe that infant saliva reacts with breast milk to form hydrogen peroxide at high enough levels to kill opportunistic pathogens, but allow others to grow.  In order to test their hypothesis, the researchers combined breast milk and infant saliva and attempted to culture the pathogen Staphylococcus aureus, along with gut commensal bacteria Lactobacillus plantarum, and Escherichia coli.  They found that the mixture created concentrations of hydrogen peroxide that killed the S. aureus but allowed the commensals to grow.

Overall this paper showed that infant saliva can combine with breast milk to form physiologically relevant concentrations of hydrogen peroxide.  The hydrogen peroxide may in fact select for the growth of specific bacteria in the mouth and gut, and lead to the development of a healthy microbiome.  Interestingly, pasteurized cow’s milk and infant formula did not contain XO, the enzyme necessary to create the hydrogen peroxide, adding another reason why there is no true substitute for breast milk.   

New research shows that Bifidobacteria transfer from mother to child

Both natural birth (as opposed to birth by C-section) and breastfeeding are topics that stir up a lot of conversation among mothers and the scientific community. For example, there is the question of whether breastfeeding rather than formula feeding has some specific benefit to an infant’s health. Well, what about the infant’s gut microbial health? A new article published by Applied and Environmental Microbiology takes a look at whether natural birth and breastfeeding coincides with an exchange of bacteria from mother to child.

Four mother and infant pairs were included in the study that was meant to discover whether the mother transfers any bacterial strains to the infant during vaginal birth and breastfeeding. In particular, the scientists were looking at the genus Bifidobacterium because this group has been known to be early colonizers of the infant gut. In addition, this genus has specific ways of digesting a human mother’s milk. Mother-infant pairs 2 and 4 exclusively breastfed, while pairs 1 and 3 supplemented with formula. Milk samples were collected from the mothers and fecal samples were collected from the mothers and children.

After sequencing the bacteria, B. adolescentis, B. angulatum, B. breve, B. dentitum, B. pseudolongum and B. thermacidophilum were found to be common between all of the mother and the infant fecal samples. The scientists then looked to see which bacteria were in both the mother’s milk and the infant’s fecal sample. The results suggest that the milk may be responsible for transferring B. adolescentis, B. angulatum, B. breve, B. longum and B. pseudolongum to the infant. Interestingly, there were also some bifidobacteria strains that were unique to the infant, suggesting that either they went undetected in the mother or that the infant was exposed to this bacteria from somewhere else.

After six months, samples were collected again in order to see how/if the sample compositions change. The scientists found that, especially in the infants, the abundance of bifidobacteria decreases. This is most likely due to changes in diet – less breastfeeding and more formula feeding – and perhaps environmental exposure. All in all, the results of this experiment shows that the infant microbiome might indeed be influenced by a vertical transfer of bacteria from mother to child. With more evidence of this as a possibility, science may begin looking into more complete analyses with larger study sizes.  

Breastmilk varies between mothers – affects microbiome of infant

Chemical structure of fucose molecule

We know that breastmilk is crucial to the development of a healthy infant’s microbiome.  It contains many oligosaccharides that cannot be digested by the infant, and whose primary purpose appears to be stimulating the growth of specific microbiome bugs.  There are, however, differences between new mothers’ milk.  For instance, some mothers cannot produce 2′-fucosylated oligosaccharides, which are oligosaccharides that have a fucose sugar on the end.  David Mills and his team at UC Davis recently investigated how the microbiomes of infants differed based on the presence or absence of fucosylated glycans in the milk that they drank.  They published their work in the journal Microbiome last week.

Forty four infants who were fed breast milk had their microbiomes measured throughout the first 120 days of their lives.  Thirty two of these infants were fed milk from woman with fucosylation ability (secretors), and twelve were from women without the fucosylation ability (non-secretors).  When the researchers investigated the contents of the milk they found that it varied in many ways, besides fucosylation.  For example, those women that did not fucosylate appeared instead to increase their monosaccharide sialylation, a sugar that has been linked to C. difficile infection.  When the scientists compared the infants’ microbiomes in the two groups they discovered that secretor-fed infants achieved higher levels of Bifidobacteria and Bacteroides, and achieved these levels more quickly than non-secretor-fed infants.  Instead, the non-secretor-fed infants had relatively higher levels of Enterobacteria, Clostridia, and Streptococci.

These differences may be important to the infants’ developments.  For example, Bifidobacteria in the gut is associated with lower gut permeability and less inflammation.  Also, Bifidobacteria and Bacteroides are large contributors to the production of short chain fatty acids and lactate, which have each been associated with gut health time and time again.  A full 20% of the U.S. population is non-secretors, and it would be interesting to see if any epidemiologically significant differences exist between the two groups into adulthood.  In either case, in the future it may be worth considering supplementing infant milk with fucosylated oligosaccharides if the lack of fucosylation does turn out to be detrimental to the baby.