The human gastrointestinal tract represents one of themost densely
populated microbial ecosystems detected to date. Although this microbial
group has been recognized to have a crucial impact on human
health, its precise composition in the first period of life is still subject
to intense investigation. Before birth, the gastrointestinal tract of the
fetus is sterile, and only during the initiation of the delivery process
and thereafter, acquisition of microbes is ongoing and time-dependent