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 The Westin Bonaventure’s main kitchen hadn’t been inspected for eight months when an outbreak of Shigella, a bacterium that can spread through infected food, hit late last August. Andrew J. Campa, Los Angeles Times, 17 Mar. 2024 The disease is caused by the bacterium Salmonella typhi, which was well-described and identifiable with diagnostic tests by the 1890s. Sabrina Sholts, Smithsonian Magazine, 12 Mar. 2024 This little remnant of a bacterium might be the source of some tools eukaryotic cells use to kill themselves. Quanta Magazine, 6 Mar. 2024 Botox is an injection of the botulinum toxin, made by the bacterium Clostridium botulinum, which blocks nerve signals and in turn, forces the muscles to relax. Korin Miller, Health, 26 Feb. 2024 The bubonic plague is caused by Yersinia pestis, a bacterium that was likely first introduced in North America around 1900 from rats on ships coming from South Asia, according to Timothy Brewer, M.D., professor of medicine and epidemiology at UCLA. Melissa Rudy, Fox News, 16 Feb. 2024 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

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 28 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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