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

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Etymology

Origin of microorganism

First recorded in 1875–80; micro- + organism

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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

If these enzymes are attached directly to the outside of a bacterium, they could allow the microorganism to digest the surrounding material while remaining in close contact with it.

From Science Daily ● Oct. 16, 2026

Yet this everyday microorganism may also offer insight into a far bigger question: how life might endure the extreme conditions found beyond Earth.

From Science Daily ● Feb. 8, 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

"You couldn't expect a microorganism to evolve here that was capable of feeding on Earth-type tissues; they would have starved to death long ago."

From Islands of Space by John Wood Campbell

Landfills often record elevated underground temperatures that happen when microorganisms break down waste.

From Los Angeles Times ● Oct. 29, 2026

Macrophages, the white blood cells responsible for engulfing and destroying harmful microorganisms, attempt to consume these particles.

From Science Daily ● Oct. 23, 2026

However, antibiotics that target a wide range of bacteria can upset the delicate balance of microorganisms in the gut.

From Science Daily ● Oct. 20, 2026

This procedure aims to restore a healthier balance of gut microorganisms, but it can be complicated to perform and unpleasant for patients.

From Science Daily ● Oct. 20, 2026

On the other hand, it was argued that, on so windy a planet as Mars, microorganisms should be everywhere if they are anywhere.

From "Cosmos" by Carl Sagan

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Related Words

• bacterium
• microbe
• pathogen
• virus

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