microorganism

American  

[mahy-kroh-awr-guh-niz-uhm] / ˌmaɪ kroʊˈɔr gəˌnɪz əm /

noun

microorganisms plural

1. any organism too small to be viewed by the unaided eye, as bacteria, protozoa, and some fungi and algae.

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microorganism British  

/ ˌmaɪkrəʊˈɔːɡəˌnɪzəm /

noun

1. any organism, such as a bacterium, protozoan, or virus, of microscopic size

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microorganism Scientific  

/ mī′krō-ôr′gə-nĭz′əm /

1. 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.

2. See Note at germ

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Other Word Forms

Derived Forms

• microorganic
  adjective
• microorganismal
  adjective

Inflected Forms

Nouns

• microorganisms
  plural

Etymology

Origin of microorganism

First recorded in 1875–80; micro- + organism

Explanation

A microorganism is a living thing that is too small to see with the naked eye. Bacteria and amoebas are microorganisms, and while not technically "alive," viruses are also considered microorganisms. The only way to see a microorganism is through a microscope, an instrument used to magnify images of very small things. Microorganisms are fundamental to life on Earth. They decompose dead things, recycle nutrients, aid in digestion, and strengthen our immune systems. They are a key part of biotechnology: Microorganisms are used to treat sewage, clean up pollution, and create medicines. Microorganisms are also used in making foods like bread and cheese. On the negative side, a few microorganisms are harmful, as they can cause disease. Another word for microorganism is microbe.

Example Sentences

See Examples For:

microorganism microorganisms

This microorganism is frequently used in laboratory studies because it possesses an extremely small genome.

From Science Daily ● Mar. 14, 2026

“The presence of terrestrial microorganism within a sample of Ryugu underlines that microorganisms are the world's greatest colonizers and adept at circumventing contamination controls,” the authors conclude.

From Salon ● Nov. 24, 2024

Mr. Gutman is the founder of Primer’s Yeast, a company that sells ancient strains of the microorganism.

From New York Times ● Jun. 20, 2024

The microorganism also been connected to non-fatal, but sight-threatening, eye infections, sometimes through contaminated contact lens solution.

From Seattle Times ● Mar. 13, 2024

And the same thing happens when a Venerian is attacked by an Earthly microorganism.

From Islands of Space by Campbell, John Wood

One possible factor is the gut microbiome, the enormous community of bacteria and other microorganisms living in the digestive system.

From Science Daily ● Jul. 17, 2026

This exposed the animals to the wide variety of viruses and microorganisms found in their normal environment.

From Science Daily ● Jun. 30, 2026

That suit, which was joined by 31 states, alleged that Abbott had a “culture of concealment” at Sturgis and “withheld information from FDA related to the presence of microorganisms in the Sturgis facility.”

From The Wall Street Journal ● Jun. 29, 2026

Unlike their chemical counterparts, biofertilisers contain live microorganisms that help plants access nutrients already present in the soil.

From Barron's ● Jun. 16, 2026

I pulled out my phone and searched “human microbiome” to reread Wikipedia’s introduction to the trillions of microorganisms currently inside me.

From "Turtles All the Way Down" by John Green

Related Words

• bacterium
• microbe
• pathogen
• virus