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[mahy-kroh-awr-guh-niz-uh m] /ˌmaɪ kroʊˈɔr gəˌnɪz əm/
any organism too small to be viewed by the unaided eye, as bacteria, protozoa, and some fungi and algae.
Origin of microorganism
First recorded in 1875-80; micro- + organism
Related forms
[mahy-kroh-awr-gan-ik] /ˌmaɪ kroʊ ɔrˈgæn ɪk/ (Show IPA),
microorganismal, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for microorganisms
Contemporary Examples
Historical Examples
  • All such very small plants and animals are known as microorganisms.

    General Science Bertha M. Clark
  • The virulence is not great enough to kill a sufficiently high percentage of rats that eat food containing the microorganisms.

    House Rats and Mice David E. Lantz
  • The diseases resulting from the microorganisms are not contagious and do not spread by contact of diseased with healthy animals.

    House Rats and Mice David E. Lantz
  • However, very few experiments have been performed to determine the importance, if any, of these microorganisms to the host.

  • The passage of microorganisms through the digestive tract of Blaberus craniifer mounted under controlled conditions.

  • Phagocytosis: the destruction or devouring of bacteria or other microorganisms by phagocytes.

  • Ameba are microorganisms of the simplest structure—a protoplasm which is constantly changing in shape.

  • The destructive effect of microorganisms both in the interior of the cheese and upon its surface is rapid.

    The Book of Cheese

    Charles Thom and Walter Warner Fisk
British Dictionary definitions for microorganisms


any organism, such as a bacterium, protozoan, or virus, of microscopic size
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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microorganisms in Medicine

microorganism mi·cro·or·gan·ism (mī'krō-ôr'gə-nĭz'əm)
An organism of microscopic or submicroscopic size, especially a bacterium or protozoan.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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microorganisms in Science
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 © 2002. Published by Houghton Mifflin. All rights reserved.
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microorganisms in Culture

microorganisms definition

Organisms so small that they can be seen only through a microscope. (See bacteria, protozoa, and viruses.)

The New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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