This biofilm shows the diverse and abundant microbes living on a single epithelial cell from the surface of the human tongue. Researchers are starting to understand how often the cells in our microbiomes are acquired from other people.
Our bodies consist of about 30 trillion human cells, but they also host about 39 trillion microbial cells. These teeming communities of bacteria, viruses, protozoa and fungi in our guts, in our mouths, on our skin and elsewhere — collectively called the human microbiome — don’t only consist of freeloaders and lurking pathogens. Instead, as scientists increasingly appreciate, these microbes form ecosystems essential to our health. A growing body of research aims to understand how disruptions of these delicate systems can rob us of nutrients we need, interfere with the digestion of our food, and possibly trigger afflictions of our bodies and minds.
But we still know so little about our microbiome that we are just starting to answer a much more fundamental question: Where do these microbes come from? Can they spread from other people like a cold virus or a stomach bug?