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 compare archaea, eukaryote
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.
Example Sentences
Recent Examples on the Web So yes, the astonishing size of the bacterium is, well, big news. 
Caroline Delbert, Popular Mechanics, 12 July 2022 Climate change is similarly suspected to be behind the geographic expansion of a dangerous bacterium, Vibrio vulnificus, which can cause flesh-eating infections known as necrotizing fasciitis. Elisha Fieldstadt, NBC News, 12 July 2022 The procedure has made the biggest strides in treating recurring infections of a deadly bacterium called Clostridioides difficile, or C. diff. Ryan Cross, BostonGlobe.com, 6 July 2022 Marmots living in the area today have fleas that carry a strain of the bacterium—and the researchers say that this strain is likely related to the ancient strain. Sarah Kuta, Smithsonian Magazine, 17 June 2022 In 2011, scientists first sequenced the genome of the plague bacterium -- Yersina pestis -- found in two plague victims buried in a pit in London. Katie Hunt, CNN, 15 June 2022 Each condition is caused by bacteria and can be cured with antibiotics (though drug-resistant strains of the bacterium that causes gonorrhea are on the rise). New York Times, 17 May 2022 At just five nanometers across—one 200th the length of a typical bacterium—fluorescent nanoantennas can bind to and interact with proteins on a molecular level. Joanna Thompson, Scientific American, 30 Mar. 2022 Rayner said his lab has not yet received a tick that tested positive for the bacterium that causes Lyme Disease. al, 13 June 2022 See More
Caroline Delbert, Popular Mechanics, 12 July 2022 Climate change is similarly suspected to be behind the geographic expansion of a dangerous bacterium, Vibrio vulnificus, which can cause flesh-eating infections known as necrotizing fasciitis. Elisha Fieldstadt, NBC News, 12 July 2022 The procedure has made the biggest strides in treating recurring infections of a deadly bacterium called Clostridioides difficile, or C. diff. Ryan Cross, BostonGlobe.com, 6 July 2022 Marmots living in the area today have fleas that carry a strain of the bacterium—and the researchers say that this strain is likely related to the ancient strain. Sarah Kuta, Smithsonian Magazine, 17 June 2022 In 2011, scientists first sequenced the genome of the plague bacterium -- Yersina pestis -- found in two plague victims buried in a pit in London. Katie Hunt, CNN, 15 June 2022 Each condition is caused by bacteria and can be cured with antibiotics (though drug-resistant strains of the bacterium that causes gonorrhea are on the rise). New York Times, 17 May 2022 At just five nanometers across—one 200th the length of a typical bacterium—fluorescent nanoantennas can bind to and interact with proteins on a molecular level. Joanna Thompson, Scientific American, 30 Mar. 2022 Rayner said his lab has not yet received a tick that tested positive for the bacterium that causes Lyme Disease. al, 13 June 2022 See More Word History
Etymology
New Latin, from Greek baktērion staff
First Known Use
1835, in the meaning defined above
Phrases Containing bacterium
Kids Definition
bacterium
noun
bac·te·ri·um bak-ˈtir-ē-əm
plural bacteria
-ē-ə
: any of a group of single-celled microscopic organisms that are important because of their chemical activities and as causes of disease
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