The breast milk that a mother feeds her baby is laden with bacteria. Does that sound bad? It shouldn’t! While there are some pathogenic bacteria, most bacteria are incredibly beneficial to the life that exists on this planet. That’s especially true of bacteria that live in and on people. It turns out that most people live in a relationship with more than 150 different species of bacteria, and the individual bacteria that participate in this relationship far outnumber the human cells that make up a person’s body. In one sense, then, a person is not an individual. Instead, he or she is a walking ecosystem!
Scientists now call the collection of bacteria that lives in a person’s body the microbiome, and as the article linked above indicates, each person seems to have his or her own special mix of bacteria in that microbiome. Indeed, some researchers think that analyzing the DNA of the bacteria a criminal leaves behind can aid in identifying that criminal in cases where his or her own DNA is not available at the crime scene or too degraded to analyze properly.1
So where does an infant start collecting the bacteria that will make up his or her own microbiome? One of the sources is the breast milk that the infant drinks. It has been known for quite some time that breast milk contains bacteria, but the details have not been well studied. However, a group of Spanish researchers have begun to shed some light on those details. They studied the breast milk of 18 mothers who varied in weight, weight gain during pregnancy, and the mode in which the baby was delivered. They sampled the milk these mothers produced at three different times: the first secretions of milk produced after giving birth (called colostrum), the milk that was produced one month after giving birth, and the milk that was produced six months after giving birth. They sequenced the DNA of the bacteria found in these samples of milk, and they came up with some amazing results.2
First, they showed that the diversity of bacteria found in the breast milk was significantly higher than previously thought. In some of the samples they studied, they found the DNA of seven hundred different species of bacteria! However, they found that this mix of bacterial species did not stay constant over time. Instead, the colostrum was rich in intestinal bacteria from generas such as Weissella and Lactococcus, while the milk produced one and six months after delivery had higher concentrations of oral bacteria such as those from the genus Veillonella. The researchers note that it is possible the increase in these oral bacteria is a result of the baby contributing bacteria to the mother’s breast, so it is not clear whether this is a designed change to optimize the health of the baby or simply a result of the breastfeeding process.
Second, they found that the mothers who were obese had a significantly lower diversity of bacteria in their milk as compared to the milk of the mothers who were not obese. Now, of course, the number of women in this study is rather small, so it’s not clear how significant this comparison is. If further studies demonstrate that this correlation is real, it might indicate that obese mothers are not giving their children an ideal mix of bacteria when they are infants. It’s even possible that the lower diversity of bacteria that the infants receive predisposes them to weight gain later in life.
Third, they found that the breast milk produced by mothers who underwent planned Caesarian section deliveries was significantly different from the milk produced by the mothers who went through a vaginal delivery. Like the obese mothers, those who went through planned Caesarian section deliveries produced milk that had a significantly lower diversity of bacterial species. However, if the mother went through an unplanned Caesarian section delivery, the diversity of bacteria in her milk was much more similar to the mothers who went through vaginal deliveries!
Once again, the small number of mothers in the study means we must view this result with some skepticism, but let’s suppose the observed differences are confirmed in other studies. How can we explain that the Caesarian section delivery must be planned in order to result in a lower diversity of bacteria in the mother’s milk? The authors suggest that hormonal responses which are specific to the labor process play a role in determining the bacterial content of the mother’s breast milk. Thus, the key is not necessarily the delivery method, but the way in which the mothers experience the labor process.
Obviously, this small study has opened up a whole new area of research when it comes to infants and their development. As time goes on, I expect that more research will reveal that the mix of bacteria in a mother’s breast milk is very important in the healthy development of her baby. As a creationist, this doesn’t surprise me at all. I have stated previously that creationists have proposed that microorganisms (and even viruses) were initially created as a link between macroorganisms (like people) and the chemical richness of their surroundings. It’s not surprising, then, that babies are introduced to a wide diversity of these useful organisms shortly after they emerge from the womb.
1. Kennedy DM, Stanton J-AL, García JA, Mason C, Rand CJ, et al., “Microbial Analysis of Bite Marks by Sequence Comparison of Streptococcal DNA,” PLoS ONE 7(12):e51757 doi:10.1371/journal.pone.0051757, 2012
Return to Text
2. Cabrera-Rubio R, Collado MC, Laitinen K, Salminen S, Isolauri E, and Mira A., “The human milk microbiome changes over lactation and is shaped by maternal weight and mode of delivery,” American Journal of Clinical Nutrition, 96(3):544-51, 2012
Return to Text