Microscopic organisms (also referred to as microbes) that exist in their single-celled form or in a colony of cells. These organisms, which cannot be seen with the naked eye, include bacteria, archaea, viruses, algae, protozoa, and fungi.

Microorganisms are so small they generally require a microscope to see. The vast majority of them pose no real threat to humans, plants, or animals. In fact, many co-evolved with us and serve beneficial functions we couldn’t thrive without.