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 team successfully isolated the nitrogenase directly from the microorganism and found that it was unusually resistant to heat.

From Science Daily ● Sep. 19, 2026

A growing number of studies have demonstrated the positive effects on the human immune system, moods and the microbiome, as the microorganism population of the body is known.

From Science Daily ● Nov. 15, 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

"No microorganisms linked to the young woman's professional work were found in her biological samples," he said.

From Barron's ● Oct. 6, 2026

Kobzev, the governor of Irkutsk, said that specialists had carried out extensive laboratory analyses of the woman’s body, and that “their results show that no microorganisms connected to her professional activities were found.”

From The Wall Street Journal ● Oct. 5, 2026

He said on Telegram that Russia's consumer and health watchdog Rospotrebnadzor had determined, following tests, that "no microorganisms linked to the young woman's professional work were found in her biological samples".

From Barron's ● Oct. 5, 2026

The gut microbiota refers to the enormous community of bacteria and other microorganisms living in the digestive tract.

From Science Daily ● Sep. 20, 2026

Might Martian microorganisms returned to Earth pose a public health hazard?

From "Cosmos" by Carl Sagan

Related Words

• bacterium
• microbe
• pathogen
• virus