THE HUMAN MICROBIOME: Background
Summary
Babies go from having very little or no microbes to having a huge list of them. As you become an adult, different enviornmental factors contribute to what makes up your microbiome and is always increasing. As people age and become senior citizens, the diversity of microbes decrease and become more similar to others around their age.[2]
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During the Pregnancy
People used to believe that the placenta was sterile. However, new research has shown that placentas were in fact carrying microbes that were not passed though the birth canal. These microbes get to the placenta through the blood stream. This is possible because of the oral microbe called Fusobacterium nucleatum. It alters blood vessels so that microbes could infiltrate the blood stream and make its way to the placenta. [3]
The diagram below shows a possible way that microbes get to the fetus throughout the pregnancy (click to magnify):
"A possible route for bacteria originating from the gut to reach the placental tissue during pregnancy. Dendritic cells (DCs) actively penetrate the epithelium, sample the microbes within the gut lumen, and transport them to the placenta, where they are presented to the fetal epithelium and immune system." [4]
Enviornmental Factors:
During pregnancy, the mother's gut microbiota changes, which affects metabolism. Because of this, whatever the mother does to her body or her microbes can positively or negatively affect the unborn child. [5]
The diagram below is an example of how the mother's diet during pregnancy can affect the baby (click to magnify):
"It is proposed that a lean woman possesses a stable, healthy gut microbiota that is modulated over the course of pregnancy (a)... Obese women (b) likely present with a disrupted gut microbiota already before pregnancy, and this is either amplified or further modified with pregnancy adaptations. These modifications lead to aberrant intrauterine environment that could lead to fetal poor/altered gut development and mediated increased chronic disease risk" [6]
During and After Birth
What makes up a baby's microbiome is dependent on what the external factors are during birth. For example, babies born of C-section have different microbiomes than babies who are vaginally born. Also, what the baby is fed in the beginning cause differences in microbiomes. [2]
Vaginal vs. C-section Birth:
As a baby is born through the vagina, it breaths in all of the bacteria on the mother. This includes bacteria such as Lactobacillus, Prevotella and Sneathia, which is important to the gut/intestines, and is found in th vaginal flora. [5]
Babies born of c-section are exposed mainly to the skin microbes of the mother and bacteria from the enviornment. This includes Staphylococcus. Although, these babies are noted to have less Bifidobacterium, a bacteria in the intestines that is used to treat diseases or conditions in the gastrointestinal tract. These babie's microbial diversity is also not as diverse. Doctors are experimenting with ways to rub bacteria collected from the mother's vagina into the baby's mouth and on its body in order to help develop their microbial diversity for the future. [5]
The diagram below shows the process of this new method being tried by doctors:
"Inoculation of the newborn with maternal microbiota restructures the microbiome after caesarean birth. Left: C-section babies get a microbiome (small red rods) upon delivery. Right: Swabbing the babies with gauze that has been in the mother's vagina transfers her vaginal microbiome (small blue rods) to her baby, resulting in a mixture of both types." [7]
Breast Fed vs Bottle Fed:
When a baby is breastfed, they are getting the best possible nutrients and bacteria sent to the gut. This includes oligosaccarides, which promotes the growth of new bacteria [5]
A baby who is fed formula is getting vitamins and other nutrients that are important, but they are not getting thier mother's bacteria, which might lead to slower development of the microbiome and a slightly highr risk for infection or problems early on. [5]
When put together, all of these factors create different ecosystems in the child. For example, one study found that delivering a baby vaginally at home, then exclusively breastfed creates the most 'beneficial' microbiome. [5]
The diagram below shows the idea that being born in different enviornments created different microbiomes (click to magnify):
"Bäckhed et al. assessed the gut microbiomes of 98 Swedish mothers and their infants during the first year of life. Cessation of breast-feeding was identified as a major factor in determining gut microbiota maturation, with distinct shifts in signature species being hallmarks of its functional maturation." [8]
Child Through Adulthood and Elder Years
Starting at 3 years of age, the microbiome is very close to how the adult microbiome looks. What makes the microbiome change is what the person does. Going through puberty, pregnancy, or menopause are times when the microbiome shifts the most. Factors like what you eat (Probiotics) and if you get sick also affect what your microbiome looks like. [2]
After the age of about 65, the diversity of the microbiome decreases.Their microbiome becomes more similar to the microbiome of others their age. [2]