Microbiome role in the gut-brain axis, part I

Hi, my name is Dagmara Zlotkowska. I would like to tell you about the microbiome role in gut-brain axis. What is the microbiome? The studies of the human microbiome started with Antonie van Leeuwenhoek, who found creatures in drop of water. In early 80s of XVII century, he compared his own fecal and oral samples. He noted the striking differences between these two habitats. Even he found differences between individuals in different stages of health and disease, in both of these sites. There are two terms related to each other. They are used interchangeably, but they have different meaning. The “microbiota” is the microbial taxa associated with humans, animals or plants. The “microbiome” is the catalog of this microbes and their genomes.

So, the human microbiome is the collection of microbes living inside and outside the human body. The microbiome significantly influences how the body operates and even outnumber human

genes by a ratio of 100:1. Some researchers evaluate the microbiota make up at about 30­50 trillion cells, human body consists from about 37 trillion cells. Do not worry, it doesn’t mean that humans are a “kind of bacteria”. Bacterial cells range from 0.2-10 microns across when human cells range from 10-100. It is believed that we carry about 330 grams of bacteria just in the intestine. The bacteria are homing our skin, hair, mucosa, intestine, reproduction tract, etc. Anyway, the microbiota are important inhabitants of human body. The others say that the gut microbiome comprises the collective genome of roughly 100 trillion microorganisms residing in the gastrointestinal tract.

The most important information is that the gene repertoire of our gut bacteria contains 150 times more unique genes than the human genome. But we don’t get born with it, because all newborns are sterile. At the moment of the birth and the lactation time, the baby’s microbiome starts to form. It is generally agreed that first contact human body with microbiota is during the birth. Babies born vaginally are colonized mostly with the Bifidobacteria as well as Lactobacilli, Bacteroides, Proteobacteria and Actinobacteria. Newborns delivered by Caesarian section are exposed mostly to skin microbes like Staphylococcus, Corynebacterium, and Propionibacterium, have more Escherichia coli, as well as Clostridia and fewer Bacteroides and Bifidobacteria. It was found that those babies are more liable for allergic diseases.

Delivery environment, home or hospital has also influence on composition of the newborn baby microbiota. Microbiota change very dynamically. Five time points significantly changing the

babies’ microbiome where distinguished: Day 0, starting breast feeding, showed a higher abundance of Bifidobacteria, in comparison to formula‐fed infants. Day 92, infants get fever. Day 134, introduction cereals to the diet. Day 161, introduction formulas and table foods. Day 371, antibiotic treatment and adult diet start. The microbes, which live in our body are determined by what we are exposed to and the colonies are instantly influx. Geography, health status, age, gender and everything we touch determine the composition of our microbiota. So it is no surprise, that the microbiome is some kind of our identification personal number, because everyone is different. Each of us has a unique microbiota and a unique microbiome.