Imagine a busy train station in the morning rush, with thousands of people moving in different directions to get on and off their trains. If you would investigate a microscope of the trillions of microorganisms in the body, it will be similar to what you just imagined. All these different species of bacteria are collectively what we call the microbiome.
What is the Microbiome?
In a healthy microbiome, all these different microorganisms live in symbiosis. The microbiome is in many ways crucial to our health and is therefore called a supporting organ . A healthy microbiota will work as a protection from pathogenic microorganisms that enter the body through food or drink by breaking the organisms down . The microbiome is found throughout the body, with the biggest part in the intestine . In the human gastrointestinal tract (GIT), there are 10 times more bacterial cells than human cells .
The microbiome is as unique as our DNA, and it’s the DNA that determines the microbiota from the beginning . In the microbiome, you will find helpful microbes, but also a few pathogenic ones. If the microbiome is healthy, there is a symbiosis within all the microbes, even the pathogenic ones. Sometimes there could be a shift in the microbiome which can cause dysbiosis. This can be caused by infectious illness, a specific diet, or the use of antibiotics. Consequently, the body might be more receptive to disease .
The most common bacterial families in the gut are Prevotella, Ruminococcos, Bacteroides, and Firmicutes. The colon is a low-oxygen environment, where anaerobic bacteria thrive like Peptostreptococcus, Bifidobacterium, Lactobacillus, and Clostridium . These bacteria might keep the level of harmful bacteria down by outliving them and taking the nutrients and attachment sites to the mucus membrane of the gut. The colon is crucial due to the immune activity taking place there, and due to the production of antimicrobial proteins .
How is the microbiota established?
The first time an infant is introduced to microorganisms is in the birth canal during the delivery and then through the breast milk . Before that, i.e. in fetal life, it is claimed that the intestine of the infant contains a small number of microbes. The infant’s intestinal microbiota is influenced by the microorganisms it is exposed to, and often has similar colonization as the vaginal microbiota of the mother .
After birth, the GIT of the infant is colonized quickly . There can be changes in the microbiome depending on the microorganisms in the surroundings and diet. This shift can be towards a healthy microbiome or a microbiome that can cause diseases . During the first year of life, there is a big change in diet when the infant is going from breast milk or formula to a more solid-based food. From the beginning, the gut microbiota is simpler and can be very individual. It is said that the infant’s initial gut colonization is crucial when establishing the adult microbiota. So, there seem to be both host-related and external factors when the microbiota is established .
The microbiome of a foetus could imitate the train station before opening. There are almost no people there yet, only a few train staff. When the station opens early in the morning, a few people will catch the first trains. As the morning continues, there will be an increase in people getting to the station. During rush-hour, it will be crowded at the train station, and this could represent a healthy and well-established microbiome.