How does your baby’s gut microbiome begin?

14 Jan How does your baby’s gut microbiome begin?

The microbiome is a popular topic within health communities, it’s benefits and contribution to a range of processes in the body are seen in emerging research. So far, it’s known to play a large role in the metabolism of our nutrients and is currently being explored in depth to determine its role in chronic disease and how it may affect our mental health. A gut microbiome is defined as the microorganisms, and their genes that live in your gut (microbiota refers exclusively to the microorganisms) – this is also known as gut flora.  Within those microorganisms, the gut encodes over 3 million genes – to put that into perspective, the human genome contains only 23 000 genes in comparison to the gut microbiota. Gut microbiota are composed of different bacteria species that are classified by genus, family, order, and phyla (many groups within groups within groups etc.). Over the past few years, new technology has allowed scientists to culture bacteria from stool samples to learn about what bacteria is present in the gut. So far, we know that bacteria that are in the Phylum ‘Firmicutes’ and ‘Bacteriodetes’ make up 90% of our gut microbiota, amongst many others. We also know that there are variations within individuals due to age, full-term or pre-term birth, diet, antibiotic use and more. Everyone’s microbiome is unique – however there are certain combinations and groups of bacteria that are commonly found within ‘healthy’ individuals (Bacteroidales and Bifidobacteriales). This does not mean however that there is only one ‘optimal’ composition as there are endless variations. The general rule is the more diverse, the better.

This microbiome is built by bacteria entering your gastrointestinal tract (GIT) – often via your mouth. However, this doesn’t mean the microbiome is exclusively developed via food! Other determining factors include mode of food delivery (fingers, spoons, via mouth or tube etc.), age and environmental exposure. The healthy development of microbiota has potential lifelong implications on your health, so how is this important environment developed in babies?

Where does the microbiome begin?

There is new research suggesting the initial introduction of bacteria to babies is via the placenta or embryotic fluid. Within the scientific community there has been a long-held belief that babies were born completely sterile. This new evidence suggests the possibility of bacteria introduced prior to birth – very exciting. Confirmation of this theory, ‘healthy’ bacteria in the womb during pregnancy, could lead to research being able to determine certain microbial profiles that cause immune conditions, or those associated with preterm birth (previously it was believed any bacteria in the womb was indicative of infection).

What we do know about vaginal birth is that babies delivered via this method, have a gut microbiota that reflect the environment of the vaginal canal of the mother which has been shown to be favourable for the development of the microbiome. Caesarean section deliveries have been shown to develop microbiomes with less Bacteroidales and Bifidobacteriales, as well as pathogens that are associated with hospital environments. This is due to the initial contact caesarean delivered babies have with hospital staff and their surroundings. A study published in October 2020, looked at the effects of conducting a maternal feacal microbiota transplantation in babies born via C-section (Korpela et al., 2020). They found that at the three month mark following administration of faecal samples via bottle-fed milk at birth, these same babies had a microbiome that reflected that of a baby born via vaginal birth. Amazing, right?!

Another factor that may impact babies’ microbiome development, is the use of antibiotics during labour. To decrease the chance of GBS (Group B Strep) being passed on to babies from GBS positive mothers, it is common practice to use antibiotics via IV during labour. Mothers that don’t receive antibiotics during labour, that are GBS positive, have a low chance of passing it on to their baby (1-2%). However, babies that develop GBS can experience very serious issues such as meningitis, sepsis and pneumonia. Unfortunately, it has been shown antibiotics like penicillin can have serious effects on the gut microbiome diversity of babies delivered via vaginal birth. The antibiotics given during labour to the mother can cause ‘good’ bacteria to be reduced along with the ‘bad’ GBS bacteria – meaning the good bacteria is less likely to be passed on to the baby. No mother or doctor wants to place the foetus at risk, yet the use of antibiotics may produce knock-on effects that cause issues later in life. More research to come on this topic.

Breastfeeding and breast milk

Breast milk is a significant source of exposure to new bacteria. Considering bacteria is often introduced via the entry to the GIT (the mouth), the choice of nutrients/food for babies is a major determinant of the composition of their microbiome. As a mother, you have the opportunity to maintain a diverse and healthy microbiome, which will then positively influence the microbiota composition in breastmilk. Babies who are breastfed often have a more complex Bifidobacterium (of the Phyla Actinobacteria) – a genus (along with Lactobacillus) that makes up a large majority of  ingredients that are used in common to encourage re-colonisation of healthy bacteria. These are known to be beneficial bacteria to possess. As probiotics aren’t commonly absorbed into circulation, there is a low chance of their effects reaching the breastmilk if taken while breastfeeding. Breastmilk is already extremely rich in pre- and probiotics to help your baby’s microbiome develop. Formula-fed infants were found to have higher rates of E coli, C difficile, and Bacteroides than breast-fed infants. These groups can be responsible for ‘taking up space’ in the microbiome, preventing other bacteria from forming to create a more diverse microbiome.

First 1000 days

The first 1000 days, like many physiological developments, is vital to develop the gut microbiota. By the age of 2-3 years old (~1000 days from conception), a child’s microbiome has developed to a point that will be similar to their microbiome for the rest of their life! The microbiome influences many functions that are related to digestion, metabolism and other factors like the development of the immune system. This is why it is crucial to provide children with a varied and nutrient rich diet as early as possible – from breastfeeding through to introduction of solids. There have been many studies that link how the early postnatal environment determines susceptibility to chronic diseases and immune disorders. If a healthy and diverse microbiome is developed in the first 3 years of life, it is likely to have major benefits to that child when they’re an adult. The mysteries of the microbiome are being continuously investigated, and in the scheme of things, it is still a very new topic in the science world. For now, we know that breastfeeding, as well as a diverse and healthy diet in both the mother and the child (as solids are introduced around 6 months of age) is the best way to nourish a healthy microbiome.

Image: Paul Rogers https://www.nytimes.com/2018/02/05/well/live/infant-microbiome-cesarean-childbirth-breastfeeding.html

References

1. What is the Healthy Gut Microbiota Composition? A Changing Ecosystem across Age, Environment, Diet, and Diseases https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6351938/
2. More than just a gut instinct–the potential interplay between a baby’s nutrition, its gut microbiome, and the epigenome https://journals.physiology.org/doi/full/10.1152/ajpregu.00551.2012
3. Association Between Breast Milk Bacterial Communities and Establishment and Development of the Infant Gut Microbiome https://jamanetwork.com/journals/jamapediatrics/article-abstract/2625334
4. Factors Influencing the Composition of the Intestinal Microbiota in Early Infancy https://pediatrics.aappublications.org/content/118/2/511?ijkey=2cc79961ce6741c3d6df2caffac17d48a7ea2726&keytype2=tf_ipsecsha
5. Bifidobacteria and Their Role as Members of the Human Gut Microbiota https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4908950/
6. Can gut bacteria improve your health? https://www.health.harvard.edu/staying-healthy/can-gut-bacteria-improve-your-health
7. Good or bad: gut bacteria in human health and diseases https://www.tandfonline.com/doi/full/10.1080/13102818.2018.1481350
8. What is the Healthy Gut Microbiota Composition? A Changing Ecosystem across Age, Environment, Diet, and Diseases (2019) https://www.mdpi.com/2076-2607/7/1/14/htm#B13-microorganisms-07-00014
9. Impact of intrapartum and postnatal antibiotics on the gut microbiome and emergence of antimicrobial resistance in infants https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6650395/
10. Group B Strep and Pregnancy https://www.acog.org/patient-resources/faqs/pregnancy/group-b-strep-and-pregnancy
11. Developmental microbial ecology of the neonatal gastrointestinal tract https://academic.oup.com/ajcn/article/69/5/1035s/4714919
12. Maternal Fecal Microbiota Transplantation in Cesarean-Born Infants Rapidly Restores Normal Gut Microbial Development: A Proof-of-Concept Study https://www.cell.com/cell/fulltext/S0092-8674(20)31089-8?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0092867420310898%3Fshowall%3Dtrue