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

"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

Scientists had long assumed that only microorganisms could break down these natural plastics.

From Science Daily ● Aug. 17, 2026

Researchers used multiple sampling techniques to determine which microorganisms lived inside Ötzi during his lifetime and which arrived after his death.

From Science Daily ● Aug. 7, 2026

This combination suggests that the microorganisms are not simply biological remains from the distant past.

From Science Daily ● Aug. 7, 2026

Candidatus Velamenicoccus archaeovorus feeds on microorganisms that convert limonene, the compound responsible for the scent of oranges, into methane and carbon dioxide.

From Science Daily ● Aug. 5, 2026

Bacteria and a host of other microorganisms could find their way into cultures from people’s unwashed hands, their breath, and dust particles floating through the air, and destroy them.

From "The Immortal Life of Henrietta Lacks" by Rebecca Skloot

Related Words

• bacterium
• microbe
• pathogen
• virus