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26 Oct 2016
A mother's breast milk is produced in order to optimise the health and nutrition of her child / children, so breast milk contains proteins, fats, carbohydrates as well as nutrients, and various immune cells. We also now know that the mother's milk contains bacteria; the composition of which appears to change throughout the duration of lactation and varies between mothers.
The current 'shared' belief is that bacteria found in the breast milk originates in the mother's gut. The transfer of maternal bacteria from the mother's intestines to her breast milk is thought to be mediated by intestinal dendritic cells1. Dendritic cells penetrate the intestinal epithelium with their projections and take up commensal bacteria from the gut lumen. These lymphocytes containing maternal intestinal microflora then travel via the gut-associated lymphatic tissue to other mucosal surfaces including the lactating mammary gland where the maternal microflora is secreted into the milk for uptake by the infant2.
In fact, specific strains that have been consumed by the mum in the form of a probiotic have been found in the breast milk; Nasiraii et al (2011) administered Lactobacillus rhamnosusLC705 to 10 of 20 women for 30 days, who were breastfeeding 1-6 month old babies. In the probiotic group, 4 of the 10 women were found to have this strain in their breast milk. Although this study is small, it is very encouraging to see that 40% of the probiotic group successfully transferred the supplemented probiotic strain into the breast milk3. Hopefully, we will see larger studies like this in the probiotics industry in the near future. In the meantime, it is not a huge leap to speculate that other high quality probiotic strains taken by mothers could pass through to the breast milk, but we will welcome more research.
There are also some other interesting theories in relation to the translocation of bacteria from the gut to the breast milk. Jeurink et al (2013) suggests that hormonal changes facilitate the movement of bacteria. Progesterone may increase gut permeability to allow for the translocation of bacteria into the bloodstream, and finally to the mammary glands in the mother's breasts4.
The gut microbiome has received a lot of scientific attention in recent decades, and rightly so as this is the habitat of choice for a lot of the bacteria we share our bodies with, but there are also other notable microbiomes around our bodies, such as the skin. Recently, a study published in the journal Scientific Reports has found that within the breasts of women is a complex ecosystem of bacteria, much different to the skin outside, forming a distinct microbiome of it's own5. Further to this, the researchers found that the breast bacteria of women with and without breast cancer differ significantly. The scientists from the Mayo Clinic utilised DNA sequencing to analyse sterile breast tissue removed from 33 women. They then compared the results to the swabs taken from breast skin, as well as cheek swabs from the same patients.
The results from the samples revealed that the microorganisms found in women with healthy breast tissue (other than benign breast disease) differed to those with confirmed cancer diagnosis. The cancer patients had a higher abundance of a variety of bacteria such as Fusobacterium, Atopobium, and Lactobacillus, differing significantly from the skin microbiome. What's interesting about this specific study is that the samples were collected in a sterile operating theatre, unlike previous studies. However, it should also be noted that the study did not collect breast tissue from women without breast abnormalities of any kind.
The study's results are intriguing, but at this stage there are a lot more questions that need answering. What exactly does the presence, or lack of, certain bacteria in the breast microbiome mean? Is the presence of the bacteria indicative of the cause of the cancer, or do they colonise the breast tissue as a result of the cancer's development? Previous studies have shown the Fusobacterium, one of the genera found in cancerous breast tissue, has previously been associated with colorectal cancers, but researchers say that more research is needed to determine exactly how the two may be linked. Tina Hieken, a Mayo Clinic oncologist and led researcher, commented:
"These bacteria might act by secreting virulence factors or by creating a pro-inflammatory environment. We'd like to look at what's really going on in the microenvironment of the tissue."
Very interesting findings in both cases, and we look forward to more clinical trials into this fascinating field of research.
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