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).

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 Abbott Laboratories in February recalled several brands and shut down a plant in Michigan after complaints that four infants fell severely ill with a dangerous bacteria after ingesting its powdered formula. The Editorial Board, WSJ, 13 May 2022 Peas: Peas should be inoculated with nitrogen-fixing bacteria known as Rhizobium to perform better. Jeff Lowenfels, Anchorage Daily News, 12 May 2022 Sellers may dilute breast milk with water or cow’s milk; the milk can also be tainted with bacteria or other dangerous contaminants that milk banks stringently monitor for. Elizabeth Chuck, NBC News, 12 May 2022 Some are even watering down formula or turning to recalled batches contaminated with dangerous bacteria. Beth Mole, Ars Technica, 11 May 2022 Food and drink recalls often involve the presence of an undeclared ingredient or contamination with dangerous bacteria or foreign material. Chris Smith, BGR, 3 May 2022 State wildlife officials are warning dog owners of the dangers of their dogs consuming salmon, steelhead, trout and other freshwater fish that are infected with potentially fatal bacteria primarily found in Northern California waters. Lauren Hernández, San Francisco Chronicle, 13 Apr. 2022 But any type of pet food, including treats, can be potentially contaminated with harmful bacteria, such as salmonella and listeria, which can lead to foodborne illnesses. Serena Coady, SELF, 9 Apr. 2022 Infections with the cronobacter bacteria are rare but can be fatal in babies. Matthew Perrone, Detroit Free Press, 25 Mar. 2022 See More

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.

First Known Use of bacteria

1864, in the meaning defined above

History and Etymology for bacteria

plural of bacterium

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Time Traveler for bacteria

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The first known use of bacteria was in 1864

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Last Updated

17 May 2022

Cite this Entry

“Bacteria.” Dictionary, Merriam-Webster, Accessed 26 May. 2022.

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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


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