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).

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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 That's like a kitchen sink cookie of bacteria-attracting, dead skin-collecting grossness. Kaitlyn Yarborough, Southern Living, "How Often Should You Be Cleaning Your Makeup Brushes? Here's the Gross Truth," 30 Apr. 2021 Several tick species found in Connecticut can spread bacteria that cause illness, according to the state Department of Public Health website ( Jesse Leavenworth,, "Connecticut facing a bad year for ticks, with more species and more diseases," 29 Apr. 2021 The Sliver Ion Sterilization filter to kill bacteria. Jim Rossman, Dallas News, "Proscenic A9 air purifier is stylish, powerful and quiet," 29 Apr. 2021 In 2017, the district experimented with an approach in which Aedes aegypti were infected with a naturally-occurring bacteria called Wolbachia that renders mosquitoes infertile and unable to carry disease. Karen Weintraub, USA TODAY, "The first genetically modified mosquitoes released in the U.S. to buzz in the Florida Keys," 29 Apr. 2021 Other important details to look out for include rubber soles, which ensure a sturdy and stabilizing stride, and antimicrobial footbeds to repel odors and bacteria. Emily Belfiore,, "The 13 Best Sandals With Arch Support for Walking Around All Day," 28 Apr. 2021 His discovery of thermophile bacteria at Yellowstone National Park in 1966 revolutionized biology and eventually enabled the development of tests for DNA traces and COVID-19. David Bressan, Forbes, "Yellowstone Supervolcano‘s Surprising Connection To Fighting Coronavirus," 28 Apr. 2021 The products could be contaminated with listeria, a bacteria that can cause foodborne illness, according to a Food and Drug Administration (FDA) announcement. Carolyn L. Todd, SELF, "Velvet Ice Cream Recall Issued For Potential Listeria Contamination," 28 Apr. 2021 With each finding, the evidence mounted: living organisms produced an innate bacteria-fighting agent. Claudia Kalb, Scientific American, "Penicillin Wasn’t Alexander Fleming’s First Major Discovery," 27 Apr. 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.

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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

Time Traveler

The first known use of bacteria was in 1864

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Statistics for bacteria

Last Updated

5 May 2021

Cite this Entry

“Bacteria.” Dictionary, Merriam-Webster, Accessed 11 May. 2021.

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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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