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

There’s also the potential for the bacterium itself to fight cancer cells. —Lauryn Higgins, Health, 9 Apr. 2024

Key Takeaways Fusobacterium nucleatum, an oral bacterium, is linked to the development of colorectal cancer. —Claire Bugos, Verywell Health, 8 Apr. 2024

Diagnosis of the fungi or bacteria responsible is difficult because sometimes the fungal pathogen or bacterium found in the wounded cane is not the pathogen that caused the canker, but a secondary invader. —Rita Perwich, San Diego Union-Tribune, 6 Apr. 2024

In this trial, researchers are evaluating the safety and efficacy of providing HMOs, in combination with the bacterium B. infantis, to adult patients with blood cancers who are undergoing stem cell transplantation. —Deborah Balthazar, STAT, 29 Mar. 2024

According to the team on this study, the main cause of death for the ants is an infection from the bacterium Pseudomonas aeruginosa (P. aeruginosa). —Laura Baisas, Popular Science, 3 Jan. 2024

Courtesy Bea Amma The bacterium is also often connected to cosmetic procedures that involve injections if the equipment is not sterilized properly, said Dr. Claire Brown, an infectious disease expert at UCLA. —Erika Edwards, NBC News, 1 Jan. 2024

Barr was by then known for her superior laboratory skills, having worked on the bacterium that causes Hansen’s disease, commonly called leprosy, as well as other projects. —Delthia Ricks, New York Times, 21 Mar. 2024

The same study also showed that tamanu oil may inhibit the growth of propionibacterium acnes and propionibacterium granulosum, two bacterium that are implicated with acne. —Sophia Panych, Allure, 29 Feb. 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