bac·​te·​ria | \ bak-ˈtir-ē-ə How to pronounce bacteria (audio) \

Definition of bacteria

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).

Keep scrolling for more

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 Antibiotics do not treat Covid, of course; but their presence in the body of a patient receiving them might allow other bacteria to develop resistance against the drugs. Maryn Mckenna, Wired, 10 Sep. 2021 Much of the discussion around pollution in the Chesapeake Bay centers on loads of nitrogen and phosphorous — nutrients capable of breeding oxygen-sucking algae blooms — and on water clarity and bacteria levels. Christine Condon,, 9 Sep. 2021 Simply put, vinegar comes from anything that has alcohol in it; bacteria turn the alcohol into acetic acid. Washington Post, 8 Sep. 2021 Scientists says this medical condition—which occurs when bacteria changes in response to the medicines used to treat infections—is detectable among brown bears in Scandinavia. David Kindy, Smithsonian Magazine, 4 Sep. 2021 For extra protection, use an antibacterial cleaner to help combat smelly bacteria buildup. Kristina Mcguirk, Better Homes & Gardens, 3 Sep. 2021 Notably, not every dog who comes into contact with Listeria bacteria will develop symptoms. Yoni Heisler, BGR, 31 Aug. 2021 While these bacteria build up an infant's gut microbiome and are overall harmless, Matson recommended patients first seek medical attention for any infection before self-treating with breast milk. Miriam Fauzia, USA TODAY, 31 Aug. 2021 To emphasize his point about rampant bureaucratic growth, Parkinson provides a series of equations, of the type an ecologist might use to model the replication of a bacteria colony. Cal Newport, The New Yorker, 30 Aug. 2021

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'bacteria.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

See More

First Known Use of bacteria

1864, in the meaning defined above

History and Etymology for bacteria

plural of bacterium

Keep scrolling for more

Learn More About bacteria

Time Traveler for bacteria

Time Traveler

The first known use of bacteria was in 1864

See more words from the same year

Dictionary Entries Near bacteria




See More Nearby Entries 

Statistics for bacteria

Last Updated

14 Sep 2021

Cite this Entry

“Bacteria.” Dictionary, Merriam-Webster, Accessed 24 Sep. 2021.

Style: MLA
MLACheck Mark Icon ChicagoCheck Mark Icon APACheck Mark Icon Merriam-WebsterCheck Mark Icon

Keep scrolling for more

More Definitions for bacteria


Medical Definition of bacteria

 (Entry 1 of 2)

plural of bacterium


bac·​te·​ria | \ bak-ˈtir-ē-ə How to pronounce bacteria (audio) \

Medical Definition of bacteria (Entry 2 of 2)

1 : bacterium not usually used technically caused by a bacteria borne by certain tiny ticksWall 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

More from Merriam-Webster on bacteria

Nglish: Translation of bacteria for Spanish Speakers

Britannica English: Translation of bacteria for Arabic Speakers Encyclopedia article about bacteria


Test Your Vocabulary

Dog Words Quiz

  • shiba puppy more or less demanding cuddles
  • Which of the following animals has a dog in its etymology?
How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

Universal Daily Crossword

A daily challenge for crossword fanatics.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!