Writing Exercise #7: Potential Factors in the Colonization of Microbial Communities in the Newborn Infant
Vaginal birth vs. C-section birth: The microbiota of the infant born vaginally is much different than one born via C-section. The microbiota of vaginally born infants is similar to that of the microbiota found in the mother’s vagina and gut, including Prevotella, Sneathis, and Lactobacillus genera. The vaginal microbiome of the mother is very important for development of defense mechanisms against disease in the infant. The microbiome is abundant in Lactobacillus, bacteria that produce lactic acid that can create a protection against pathogenic bacteria. In one study, vaginal fluids were given to C-section infants after birth. They found the microbiomes changed to that of vaginally delivered babies after one month. The microbiota of infants born by C-section is different from those born vaginally. The bacteria found in the microbiota of C-section infants resembles that of the mother’s skin and oral microbiota, including Propionibacterium, Corynebacterium and Streptococcus genera. The study we read says that a higher number of C-section babies contract MRSA (Staphylococcus aureus) infections, attributing that to their exposure to bacterial antibiotic-resistance genes and their higher “abundance” of Staphylococcus. The authors also state that C-section infants have a delayed “colonization of Bacteroidetes” and lower diversity of alpha bacteria groups in their first 2 years. Also, after a few months, the oral microbiome of C-section infants shows less diversity than vaginally delivered babies. There is some thought that because of less exposure to the mother’s vaginal microbiome as a baby that C-section babies may have a higher correlation with disease down the road, such as celiac disease, obesity and asthma etc. I’m not sure I agree with these projections, because there are many factors to take into account and they would need a very large control sample to prove or disprove long term effects. They did say that after a few months, most of the discrepancies between the microbiomes of vaginally delivered and c-section infants are resolved.
Breast fed vs. bottle fed newborns: Infant diet is one of the most important factors in the development of their microbiome. Maternal milk has been thought of as sterile from bacteria, but it has been shown recently that it contains bacteria important for establishing a healthy microbiome in the infant. The first milk a newborn drinks, called colostrum, contains a variety of bacteria, including Weisella, Leuconostoc, Staphylococcus, Streptococcus and Lactococcus. Later it changes to a flora more resembling oral cavities. It is believed that the source of the bacteria in the mother’s milk comes from the microflora of the mother’s gut, which is dependent on hormonal influences. The bacteria that the infant gets from breastfeeding helps the baby digest oligosaccharides, and smaller sugars. The bacteria in the milk helps the baby digest the nutritional contents of the milk in a symbiotic way. Studies show that the most prevalent bacteria found in the breast fed babies guts are Bifidobacteria, and in formula fed infants they are Enterococci and Clostridia. Formula fed infants also have a greater species diversity. The bifidobacterium and the bacteria important for aiding in the digestion of oligosaccharides. I am not sure how well formula fed babies are able to digest sugars.
Antibiotics given to infant or mother: Antibiotics are known to kill pathogenic bacteria, and any use of them will notably affect the microbiome of whoever is taking them. In a study done with rats, the use of common antibiotics (azithromycin, amoxicillin and cefaclor), was shown to change fecal microbiota, reduce bacteria diversity and cause weight gain. It is common for doctors to recommend taking probiotics along with antibiotics to replenish healthy bacteria, but I am not sure how safe they feel it is during pregnancy.
Oral microbiota and/or oral infection of the mother: The article we read states that they have found a similarity between the microbiota of the oral cavity and the placenta in the mother. The placental microbiome resembles the microbiome of the oral cavity more than anywhere else in the mother’s body. There is apparently a correlation between mother’s with periodontal disease and pregnancy complications. One study showed an increased risk of preterm birth with maternal periodontal disease.
Mothers diet: Obviously diet is one of the most important factors affecting a pregnant woman’s microbiome, which then affects the fetus. Bacteriodes and Staphylococcus levels were shown to be significantly higher in obese pregnant women compared to pregnant women that were normal weight. A healthy diet in general probably promotes a healthier microbiome for the mother, which can indirectly affect the fetus with a healthier pregnancy in general.
Maternal weight: Studies have shown that overweight and obese pregnant women have a higher number of bacteria from the genus Staphylococcus, including S. aureus, as well as more Lactobacillius. There is concern about the long term effects of the presence of larger amounts of S. aureus in maternal milk because of a correlation that has been made with the presence of S. aureus in the microbes of overweight children. Metabolic hormones in overweight women are thought to alter the mothers’s microbiota which could then affect the fetus.
Probiotics: A study was done where pregnant women were given probiotics and the probiotic bacteria were found in the infant meconium and placenta. This implies again that bacteria can travel from the mother and colonize in the placenta as well as break the barrier into the infant’s GI tract. The mechanisms of how this happens are still not understood. Another study showed that probiotics changed the expression of Toll-like receptor genes in the infants placenta and meconium. In addition, in another study where probiotics were used, there was a correlation between mother’s with allergic diseases taking probiotics and a reduced risk for eczema in the infants. There appears to be a number of studies on the use of probiotics and its effects on the microbiomes of mother and infant during pregnancy .
Maternal hormones: The mother’s hormones have a huge impact on her microbiome that can then affect the infant’s microbiome. The study we read says that hormonal and metabolic changes that take place during pregnancy resemble those that you see in metabolic syndrome. This involves changes in hormones intricately involved with the immune system as well. In the case of pregnancy, though, these changes are said to be healthy and supportive of the bodily changes that have to occur during pregnancy, such as inflammation required during implantation of the fertilized egg, then changing to an anti-inflammatory state later in pregnancy that allows the fetus to grow. In the third trimester of pregnancy the gut microbiota changes dramatically which would be in alignment with the fluctuation of maternal hormones.
