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, eukaryote

Examples of bacterium in a Sentence

Recent Examples on the Web

Listeria is a common and stubbornly persistent type of bacterium that thrives in the cool, damp conditions found in processing plants, unlike many other foodborne pathogens. —Andrea Chang, Los Angeles Times, 24 Oct. 2024

The type of antibiotic used depends on the bacterium causing the infection.12 The Risk of Antibiotic Resistance Some bacteria become antibiotic resistant, meaning the drugs designed to kill them are less effective or do not work at all against them. —Angelica Bottaro, Verywell Health, 13 Oct. 2024

The cosmetic drug Botox is derived from a bacterium. —Benji Jones, Vox, 20 Sep. 2024

His lungs seemed to be infected with methicillin-resistant Staphylococcus aureus (MRSA), a bacterium so hardy that few drugs can kill it. —Dhruv Khullar, The New Yorker, 2 Sep. 2024

Word History

Etymology

New Latin, from Greek baktērion staff

First Known Use

1835, in the meaning defined above

Phrases Containing bacterium

• flesh-eating bacterium
• sulfur bacterium

Kids 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