- any organism too small to be viewed by the unaided eye, as bacteria, protozoa, and some fungi and algae.
Origin of microorganism
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
Examples from the Web for microorganism
The disease is caused by a microorganism and several bacteria have been suspected of being responsible.Special Report on Diseases of the Horse
United States Department of Agriculture
Staphylococcus pyogenes aureus—a microorganism producing yellow pus.
Staphylococcus pyogenes citreus—a microorganism producing lemon-colored pus.
Staphylococcus pyogenes albus—a microorganism producing white pus.
This disease is caused by a microorganism known as the spirochaeta pallida or treponema pallidum of Schaudinn and Hoffmann.
- any organism, such as a bacterium, protozoan, or virus, of microscopic size
- An organism of microscopic or submicroscopic size, especially a bacterium or protozoan.
- An organism that can be seen only with the aid of a microscope and that typically consists of only a single cell. Microorganisms include bacteria, protozoans, and certain algae and fungi. See Note at germ.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.