23 / 92
350
YEARS
OF
SCIENCE
23
© Gérard Eberl - Institut Pasteur
The intestinal microbiota
structures a small community, protected from the external environment, that is called a biofilm. Such
biofilms may be found everywhere in nature, but also on some parts of our bodies – teeth, in particular – in
some industrial structures – such as water pipes – or, also, on some prostheses or catheters in the medical
setting. In these biofilms, bacteria may stay for several years, sheltered from antibiotics and detergents,
which raises serious medical and industrial concerns.
Other microbial assemblies, of a much larger size, may form in symbiosis with any living organism, and they
are beginning to be extremely well-documented: these are microbiota. Who hasn’t heard of the intestinal
microbiota, formerly called the gut flora? Progress achieved in genomics and transcriptomics has enabled
us to remarkably improve our understanding of how a crucial role this flora plays. It is now well established
that in an organism, a microbiota harboring a great diversity of species is a signal of good health and
that such diversity reduces
with age, that the microbiota
regulates our development
in general, and in particular
that of our immune system,
protects us from pathogens
and produces components
that may migrate to our brain
and affect our behaviour.
Microbiota
and
biofilms
are
bona fide
societies, in
which the members of a
same species talk to each
other in a specific chemical
language,
perceived
by
receptors that enable bacteria
to appreciate the number of
their sieblings present in their
close environment and with
which they can act together.
This phenomenon is called
quorum sensing
: the objective
of the group is to act together
if the quorum is reached!
For instance, a pathogen
bacterium only produces its toxins if enough bacteria of the same species are present and have a good
chance of succeeding an infection and subvert the immune defenses of the infected host. Bacteria are like
academicians, they take important decisions only if they have a quorum!