mi·​cro·​or·​gan·​ism ˌmī-krō-ˈȯr-gə-ˌni-zəm How to pronounce microorganism (audio)
: an organism (such as a bacterium or protozoan) of microscopic or ultramicroscopic size

Examples of microorganism in a Sentence

Recent Examples on the Web In extreme cases, antibiotics kill so much of the good bacteria that keeps the gut balanced that the bad, fermenting-capable fungi and microorganisms flourish. Irene Wright, Miami Herald, 3 June 2024 Gut health includes the internal ecosystem known as the gut microbiome, which is made of trillions of live microorganisms that line the gastrointestinal tract. Suzie Finkel Ms, Rd, Cdn, Health, 26 May 2024 Antimicrobial resistance occurs when the microorganisms that cause infections become resistant to antibiotics and antifungals, according to the Mayo Clinic. Sabienna Bowman, Peoplemag, 16 May 2024 Composting Process: Solid waste begins to decompose inside the composting chamber, aided by aerobic bacteria and microorganisms that break down the waste into compost. Debbie Wolfe, Popular Science, 15 May 2024 See all Example Sentences for microorganism 

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'microorganism.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


International Scientific Vocabulary

First Known Use

1880, in the meaning defined above

Time Traveler
The first known use of microorganism was in 1880

Dictionary Entries Near microorganism

Cite this Entry

“Microorganism.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/microorganism. Accessed 22 Jun. 2024.

Kids Definition


mi·​cro·​or·​gan·​ism ˌmī-krō-ˈȯr-gə-ˌniz-əm How to pronounce microorganism (audio)
: an organism (as a bacterium) of microscopic or less than microscopic size

Medical Definition


mi·​cro·​or·​gan·​ism -ˈȯr-gə-ˌniz-əm How to pronounce microorganism (audio)
: an organism of microscopic or ultramicroscopic size

More from Merriam-Webster on microorganism

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