bacterium

noun

bac·​te·​ri·​um bak-ˈtir-ē-əm How to pronounce bacterium (audio)
plural bacteria bak-ˈtir-ē-ə How to pronounce bacterium (audio)
biology : any of a domain (Bacteria) (see domain sense 8) of chiefly round, spiral, or rod-shaped single-celled prokaryotic microorganisms that typically live in soil, water, organic matter, or the bodies of plants and animals, that make their own food especially from sunlight or are saprophytic or parasitic, are often motile by means of flagella, reproduce especially by binary fission, and include many important pathogens
broadly : prokaryote

Note: Bacteria lack a nuclear membrane or membrane-bound organelles and are categorized as gram-positive or gram-negative when a cell wall is present. While many bacteria are aerobic requiring the presence of oxygen to survive, others are anaerobic and are able to survive only in the absence of oxygen.

compare archaea, eukaryote

Examples of bacterium in a Sentence

Recent Examples on the Web According to a report completed by Badger Labs in August, neither bacterium was present. Quinn Clark, Journal Sentinel, 19 Feb. 2024 The bacterium in question, Listeria monocytogenes, can cause listeriosis, a foodborne infection that is often innocuous but occasionally lethal. Jon Healey, Los Angeles Times, 15 Feb. 2024 Instead, many new cases are found in people with chronic acid reflux or infections with a bacterium called Helicobacter pylori, which can cause inflammation in the stomach. Aria Bendix, NBC News, 6 Feb. 2024 Plague is a highly deadly disease caused by infection with the bacterium Yersinia pestis. Mark Kortepeter, Forbes, 20 Feb. 2024 There is a Yersinia pestis vaccine, but Moorjani said it is recommended only for high-risk people like scientists who work directly with the bacterium. Jacqueline Howard, CNN, 13 Feb. 2024 Humans are most commonly exposed to plague from the bites of fleas carrying Yersinia pestis, the bacterium that causes the disease. Aria Bendix, NBC News, 9 Feb. 2024 According to the Centers for Disease Control and Prevention, listeria is a serious infection usually caused by eating food contaminated with the bacterium Listeria monocytogenes. Emily Deletter, USA TODAY, 19 Jan. 2024 The infant developed sepsis from the bacterium in the probiotic product—Evivo with MCT Oil made by Infinant Health—and subsequently died. Eric Berger, Ars Technica, 3 Oct. 2023

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

Word History

Etymology

New Latin, from Greek baktērion staff

First Known Use

1835, in the meaning defined above

Time Traveler
The first known use of bacterium was in 1835

Dictionary Entries Near bacterium

Cite this Entry

“Bacterium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/bacterium. Accessed 19 Mar. 2024.

Kids Definition

bacterium

noun
bac·​te·​ri·​um bak-ˈtir-ē-əm How to pronounce bacterium (audio)
plural bacteria
-ē-ə
: any of a group of single-celled microorganisms that live in soil, water, the bodies of plants and animals, or matter obtained from living things and are important because of their chemical effects and disease-causing abilities

Medical Definition

bacterium

noun
bac·​te·​ri·​um bak-ˈtir-ē-əm How to pronounce bacterium (audio)
plural bacteria -ē-ə How to pronounce bacterium (audio)
: any of a domain (Bacteria) of prokaryotic round, spiral, or rod-shaped single-celled microorganisms that may lack cell walls or are gram-positive or gram-negative if they have cell walls, that are often aggregated into colonies or motile by means of flagella, that typically live in soil, water, organic matter, or the bodies of plants and animals, that are usually autotrophic, saprophytic, or parasitic in nutrition, and that are noted for their biochemical effects and pathogenicity
broadly : prokaryote

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