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

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

Originally discovered in extreme environments like hydrothermal vents, archaea, a single-celled microorganism, can also be found in the digestive systems of animals, including humans where they play a key role in gut health.

From Science Daily ● Mar. 6, 2024

The disease is caused by a microorganism and several bacteria have been suspected of being responsible.

From Special Report on Diseases of the Horse by Charles B. Michener

Using microorganisms to manufacture useful substances is already well established.

From Science Daily ● Sep. 13, 2026

Preliminary findings suggest that the therapies may reduce bacterial species associated with periodontal disease while increasing microorganisms linked to healthier gums.

From Science Daily ● Aug. 30, 2026

UV radiation is deadly enough to many microorganisms that hospitals routinely use it for sterilization.

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

It has recently been reported that the nucleic acid of chloroplasts is, in fact, homologous with that of certain photosynthetic microorganisms.

From "The Lives of a Cell" by Lewis Thomas

Related Words

• bacterium
• microbe
• pathogen
• virus