bacterium
noun
bac·te·ri·um
| \ bak-ˈtir-ē-əm
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\
plural bacteria\ bak-ˈtir-ē-ə
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\
Definition of bacterium
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, eukaryoteExamples of bacterium in a Sentence
Recent Examples on the Web
Participating neighborhoods are sprayed with a special tick-killing fungus, or dotted with bait boxes that trap tiny mammals, like white-footed mice, from which ticks acquire the Lyme bacterium. — Micah Hauser, The New Yorker, "Tickbusters on the Lookout for Lyme," 22 July 2019 Also, drug therapies that target toxic proteins released in the brain by bacterium may slow or halt the progression of Alzheimer’s. — Cindy Krischer Goodman, sun-sentinel.com, "New clues about why people get Alzheimer’s and how to fight it," 19 July 2019 The bacterium then uses these chemicals as food sources. — The Economist, "An enzyme that digests plastic could boost recycling," 16 Apr. 2018 Inside the insect, the bacterium releases a protein that causes the pest to die within a few days. — The Editors Of Organic Life, Good Housekeeping, "The 7 Best Organic Pest Control Techniques For Your Garden," 18 Dec. 2017 These mini-donut-sized Mosquito Dunks contain BTI, a bacterium that's lethal to mosquito larvae, black flies and fungus gnats for up to 30 days, but won't harm plants or animals (including humans). — Los Angeles Times, "Pollinators & predators in your garden: How to save one, kill the other," 17 July 2019 The main reason to do that is to cure a devastating, diarrhea-causing infection by Clostridioides difficile, the bacterium usually known as C. diff (and formerly called Clostridium difficile). — Maryn Mckenna, WIRED, "The Death of a Patient and the Future of Fecal Transplants," 11 July 2019 The infection is caused by the bacterium Mycoplasma gallisepticum, which is common in domestic turkeys and chickens. — Joan Morris, The Mercury News, "Contagious house finch eye disease reported in Walnut Creek area," 17 June 2019 The bacterium behind the outbreak was a particularly nasty strain of Shiga toxin-producing Escherichia coli O157:H7 that produces only Shiga toxin type 2 (Stx2), the more toxic of two types of toxins E. coli tends to carry. — Beth Mole, Ars Technica, "The poop of 100K cows may be to blame for that deadly romaine E. coli outbreak," 8 Aug. 2018These example sentences are selected automatically from various online news sources to reflect current usage of the word 'bacterium.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.
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More Definitions for bacterium
bacterium
noun
English Language Learners Definition of bacterium
: any one of a group of very small living things that often cause disease
See the full definition for bacterium in the English Language Learners Dictionary
bacterium
noun
bac·te·ri·um
| \ bak-ˈtir-ē-əm
\
\
plural bacteria\ -ē-ə \
Kids Definition of bacterium
: any of a group of single-celled microscopic organisms that are important to humans because of their chemical activities and as causes of disease
bacterium
noun
bac·te·ri·um
| \ bak-ˈtir-ē-əm
\
\
plural bacteria\ -ē-ə
\
\
Medical Definition of bacterium
: 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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