What is the microbiota?

Microbiota means « little living » and is the recent name given to the entire microbial community living in symbiosis with our body. It comprises mainly what was further called the gut flora but does not restrict to it. Microorganisms can be found on every surface and in every cavity of our body. Even straight out of the shower, we are carrying 10 times more bacteria that the total number of our human cells, that is hundreds of billions, which sums up for 1 to 2 kg of our body weight.

WHAT IS THE ROLE OF MICROBIOTA?
This entire little world is essential for the function of human body. In particular, it:
•    helps us digest food ingredients,
•    synthesizes some vitamins such as folic acid (B12) and vitamin K.
•    maintains the integrity of the gut mucosa, which functions as a selective filter
•    prevents the settling of pathogenic microbes
•    contributes to the maturation of the immune system.

THE METAGENOME : OUR SECOND GENOME
The recent development of new genomics technologies has allowed the first insights into the genetic material of the microbiota, which contains about 150 times more genes than the human genome and is called metagenome (the Greek prefix meta stands for « on top of ») (1). The first results have shown that, despite the high variability of the bacterial mix from one individual to another, there is an important core set of common genes, which are involved in metabolic pathways. Metagenomics is also allowing us to look at differences in the microbiota composition according to populations, age, food habits, diseases or specific environmental exposures.

ALTERATIONS OF THE MICROBIOTA THROUGH LIFE
The first contact with the microbiota occurs at birth, when the newborn passes through the genital tract of the mother. Until 2 years of age, when it is considered mature, the microbiota is getting more and more complex. During adult life, changes are rather scares in healthy individuals. However, in elderly people, alterations are progressively implementing themselves, mainly due to nutritional changes, increased incidence of diseases and higher intake of medication (2, 3). Some bacterial species are declining, probably leading to immune frailty (4).

MICROBIOTA AND MEABOLIC DISEASES
Microbial balance and integrity of the intestinal walls are crucial for good health. A loss of balance (dysibiosis) can trigger digestive dysfunctions, allergies in children and chronic conditions including obesity and inflammatory diseases (5). In particular, comparative studies have shown that obese people present a composition of microbiota, different from the lean ones (6).

WHEN OUR MICROBES TALK TO OUR BRAIN
The microbiota seems to be in constant dialog with our brain, so that researchers are beginning to gather some clues that it could actually affect our behavior (7, 8).

HOW CAN WE INFLUENCE ON OUR MICROBIOTA?
Innovative insights into the microbial world offer a promising perspective for the development of active bioingredients, specifically aiming at maintaining a healthy gut microbiota. To date, the ingredients able to influence on the microbiota are either probiotics or prebiotics, as well as their combinations (synbiotics).

Probiotics are live microorganisms capable of restoring a balanced microbiota when given at adequate doses.
Prebiotics are non-digestible food ingredients able to specifically stimulate the growth or activity of some gut bacteria.

Although some feeding trial have already shown promising results with these supplements (for overview see (9)), further longer-term investigations are required to substantiate their use in elderly healthcare fields.