The bacteria in our body outnumber our own cells by about 10 to 1, with most of them found in our gut. Over the last few years, it has become clear that the bacterial ecosystem in our body – our microbiome – is essential for developing and maintaining a healthy immune system.
Our gut bugs also help to prevent germs from invading our bodies, and help to absorb nutrients from food.
A baby gets its first major dose of bacteria in life as it passes through its mother's birth canal. En route, the baby ingests the mother's vaginal microbes, which begin to colonise the newborn's gut.