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

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

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

Moreover, this approach has facilitated the investigation into molecular mechanisms underlying electrical conductivity in Shewanella oneidensis MR-1, a model electrogenic microorganism.

From Science Daily ● Feb. 29, 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.

Cold-adapted microorganisms can function at temperatures that would slow or stop many other species.

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

The team detected several human mitochondrial DNA lineages, as well as a diverse microbiome made up of bacteria, fungi and salt-loving microorganisms.

From Science Daily ● Aug. 4, 2026

These measurements reveal how much CO2 microorganisms have released after consuming organic material.

From Science Daily ● Aug. 3, 2026

The medical community didn't know that microorganisms transmitted by mosquitoes, which thrive in wet areas, produce malaria.

From "Ambushed!" by Gail Jarrow

Related Words

• bacterium
• microbe
• pathogen
• virus