bacterium
Americannoun
noun
plural
bacteria-
Any of a large group of one-celled organisms that lack a cell nucleus, reproduce by fission or by forming spores, and in some cases cause disease. They are the most abundant lifeforms on Earth, and are found in all living things and in all of the Earth's environments. Bacteria usually live off other organisms. Bacteria make up most of the kingdom of prokaryotes (Monera or Prokaryota), with one group (the archaea) sometimes classified as a separate kingdom.
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See also archaeon prokaryote
Usage
It is important to remember that bacteria is the plural of bacterium, and that saying a bacteria is incorrect. It is correct to say The soil sample contains millions of bacteria, and Tetanus is caused by a bacterium.
Etymology
Origin of bacterium
1840–50; < New Latin < Greek baktḗrion, diminutive of baktēría staff; akin to báktron stick, Latin baculum, bacillum
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
So a lot of the focus is on changes to the bacterium and whether people have less immunity.
From BBC • Mar. 27, 2026
Does the explanation for its scale and speed lie solely in the bacterium itself or did other factors play a role?
From BBC • Mar. 20, 2026
An initial genetic analysis of the bacterium causing the outbreak was concluded on Thursday.
From BBC • Mar. 20, 2026
This is partly because the bacterium forms spores that can survive treatment and later grow into new bacteria.
From Science Daily • Mar. 11, 2026
Allys begins her discussion with some review of the manipulation of the Bt bacterium to create pest-resistant crops, and the introduction of transgenic animals into the food supply decades ago.
From "The Adoration of Jenna Fox" by Mary E. Pearson
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
