bacteria

noun

bac·​te·​ria bak-ˈtir-ē-ə 

plural of bacterium

diseases caused by bacteria

Overprescribing antibiotics can contribute to the development of antibiotic-resistant bacteria.

—Maanvi Singh

Note: Microscopic single-celled organisms lacking a distinct nucleus are known as bacteria. They may be shaped like spheres, rods, or spirals. They inhabit virtually all environments, including soil, water, organic matter, and the bodies of animals. Many bacteria swim by means of long whiplike structures called flagella. The DNA of most bacteria is found in a single, circular chromosome, and is distributed throughout the cytoplasm rather than contained within a membrane-enclosed nucleus. Though some bacteria can cause food poisoning and infectious diseases in humans, most are harmless and many are beneficial. They are used in various industrial processes, especially in the food industry (for example, in the production of yogurt, cheeses, and pickles).

About Viruses and Bacteria: Usage Guide

Viruses differ from bacteria in several important ways. Viruses are not living organisms; they can only replicate in the cells of a host. By contrast, bacteria are single-celled organisms that can reproduce on their own and are many times larger than viruses. While both viruses and bacteria can cause disease, most bacteria are harmless and many are beneficial.

Examples of bacteria in a Sentence

Recent Examples on the Web

Moisture and bacteria buildup in drains are common sources of odors that regular cleaning can prevent. —Kate Van Pelt, The Spruce, 22 Jan. 2026

The study notes that dragon’s blood can inhibit the growth of certain bacteria and fungi for both the tree itself and for humans who use it medicinally. —Scott Travers, Forbes.com, 21 Jan. 2026

First, yeast turns the sugar in apple cider into alcohol, then bacteria turn that alcohol into acetic acid, the main component of vinegar. —Kirsten Nunez, Martha Stewart, 21 Jan. 2026

While the research is limited at the moment, our experts agreed that high-frequency wands have the potential to reduce acne-causing bacteria in skin (thus minimizing breakouts), calm redness and inflammation, and enhance circulation. —Deanna Pai, Vogue, 20 Jan. 2026

Word History

Etymology

plural of bacterium

First Known Use

1864, in the meaning defined above

Rhymes for bacteria

• arteria
• criteria
• diphtheria
• egeria
• listeria
• neisseria
• wisteria
• cafeteria
• cyanobacteria
• mycobacteria

Kids Definition

bacteria

plural of bacterium

Medical Definition

bacteria

1 of 2

plural of bacterium

bacteria

2 of 2 noun

bac·​te·​ria bak-ˈtir-ē-ə 

1

: bacterium

—not usually used technically

caused by a bacteria borne by certain tiny ticks

—Wall Street Journal

a single bacteria—there are roughly 200 in each cough—apparently can infect a person

—Cheryl Clark

2

plural capitalized : a domain in the system of classification dividing all organisms into three major domains of life that includes the prokaryotes that are bacteria but not those that are archaea compare eubacteria