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).

Is bacteria singular or plural?: Usage Guide

In its established and uncontroversial uses, bacteria is the plural of bacterium.

… many of the bacteria isolated from these deep environments are anaerobic …

—Stephen Jay Gould

In speech and in some, typically nontechnical, journalistic writing, it also occurs in a singular sense, synonymous with bacterium.

Lyme disease is a potentially serious arthritis-like ailment caused by a bacteria borne by certain tiny ticks.

—The Wall Street Journal

… this bacteria is closely associated with poor health and, in old people, frailty …

—Leah Hardy

Although the singular use of bacteria is often identified as an error to be avoided, it is common in published writing. The plural form bacterias is also seen but is relatively rare.

The bacteria seems to prefer living in water and is more resistant to chlorine and elevated water temperatures than other bacterias.

—Allan Bruckheim

Examples of bacteria in a Sentence

Recent Examples on the Web

The presence of chemosynthetic bacteria in an underground, anoxic environment supports the idea that early life may have originated in similar settings. —Scott Travers, Forbes, 2 Mar. 2025

Some reasons a food recall might be issued is due to undeclared allergens or the presence of bacteria. —Dan Perry, Newsweek, 2 Mar. 2025

People who regularly ate citrus were shown to have beneficial gut bacteria that may boost the production of serotonin and dopamine. —Emily Kay Votruba, EverydayHealth.com, 28 Feb. 2025

Part of this is due to the ecosystems surrounding cancerous tumors, which possess their own microbial communities that include fungi, viruses, and bacteria. —Andrew Paul, Popular Science, 27 Feb. 2025

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 archaebacteria or archaea compare eubacteria