The phrase "microbial cells" refers to very tiny living organisms that cannot be seen with the naked eye. They are made up of a single cell and include bacteria, viruses, and fungi. Full definition
In fact, there are over 10 times more microbial cells in our bodies than human cells. (mindbodygreen.com)
They are so common that for every human cell of your body, there are 10 microbial cells living in and on you. (healthyeating.sfgate.com)
In recent years, research has shown that what people commonly think of as «their» bodies contain roughly 10 microbial cells for each genetically human one. (sciencenews.org)