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

The authors contend that no facility currently operating on Earth can guarantee complete containment, elimination, or control of an unknown alien microorganism if an accident were to occur.

From Science Daily ● Jul. 6, 2026

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

This microorganism is transmitted to the healthy birds by the feed, or water becoming contaminated with the discharges from the diseased birds.

From Common Diseases of Farm Animals by R. A. Craig, D.V.M.

The microorganisms transform them into new food components, including proteins, fats, and acids.

From Science Daily ● Sep. 13, 2026

Using microorganisms to manufacture useful substances is already well established.

From Science Daily ● Sep. 13, 2026

The result is a patchwork of shadowed areas that can stay extremely cold, preserve water, and protect delicate molecules and potential microorganisms from damaging radiation.

From Science Daily ● Aug. 25, 2026

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

From Science Daily ● Aug. 17, 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