bacterium
noun
bac·te·ri·um
bak-ˈtir-ē-əm 
plural bacteria
bak-ˈtir-ē-ə
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
Listeria is a particularly resilient bacterium that can cause severe health complications, particularly for pregnant women, the elderly, newborns and those with weakened immune systems.
—
David Faris, Newsweek, 3 Nov. 2024
One of the most serious risks of eating unheated deli meat during pregnancy is the possibility of developing listeriosis, an infection caused by the bacterium listeria monocytogenes, says Dr. Carolyn Cokes, MD, MPH, a board certified OB/GYN with the Metropolitan OB/GYN group.
—Caroline C. Boyle, USA TODAY, 26 Oct. 2024
But listeria, a common and stubbornly persistent type of bacterium, presents unique hurdles.
—Andrea Chang, Los Angeles Times, 24 Oct. 2024
Liber Pater wines are made on a tiny patch of land in the Graves region of Bordeaux, one of the few places unaffected by the phylloxera bacterium that destroyed vineyards across Europe in the mid-19th century.
—Matteo Atti, Forbes, 4 Oct. 2024
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David Faris, Newsweek, 3 Nov. 2024
One of the most serious risks of eating unheated deli meat during pregnancy is the possibility of developing listeriosis, an infection caused by the bacterium listeria monocytogenes, says Dr. Carolyn Cokes, MD, MPH, a board certified OB/GYN with the Metropolitan OB/GYN group.
—Caroline C. Boyle, USA TODAY, 26 Oct. 2024
But listeria, a common and stubbornly persistent type of bacterium, presents unique hurdles.
—Andrea Chang, Los Angeles Times, 24 Oct. 2024
Liber Pater wines are made on a tiny patch of land in the Graves region of Bordeaux, one of the few places unaffected by the phylloxera bacterium that destroyed vineyards across Europe in the mid-19th century.
—Matteo Atti, Forbes, 4 Oct. 2024
See all Example Sentences for bacterium
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Cite this Entry
“Bacterium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/bacterium. Accessed 30 Nov. 2024.
Copy CitationKids Definition
bacterium
noun
bac·te·ri·um
bak-ˈtir-ē-əm
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
plural bacteria
-ē-ə
: 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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