bac·te·ria | \ bak-ˈtir-ē-ə \
plural bacteria also bacterias

Definition of bacteria 

: bacterium not usually used technically

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Is bacteria singular or plural?: Usage Guide

Bacteria is regularly a plural in scientific and pedagogical use; in speech and in journalism it is also used as a singular, and it is sometimes pluralized as bacterias. caused by a bacteria borne by certain tiny ticks Wall Street Journal more resistant to chlorine and elevated water temperatures than other bacterias —Allan Bruckheim, M.D., Chicago Tribune These journalistic uses are found in British as well as American sources.

Did You Know?

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 whip-like 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).

Examples of bacteria in a Sentence

Recent Examples on the Web

Legionnaires’ disease is a type of pneumonia that is caused by the bacteria Legionella, which grows in warm water. Carl Campanile, Fox News, "Legionnaires' outbreak sickens 8 in NYC," 13 July 2018 Of 633 outbreaks nationwide caused by bacteria, viruses or other things floating around, nearly 80 percent of them were traced to water that was treated with chlorine or other chemicals in swimming pools, hot tubs or wading pools. Glenn Howatt,, "Swimming pools, hot tubs are more likely than lakes to make you sick, studies find," 11 July 2018 The overuse of antibiotics is being blamed for contributing to the rise of life-threatening human infections caused by antibiotic-resistant bacteria. Alexa Imani Spencer, USA TODAY, "Pizza Hut flaps about eliminating antibiotics from chicken wings, toppings by 2022," 19 June 2018 He was later felled by a flesh-eating bacteria that could have cost him his life. Steve Helling,, "Naked and Alone: How Matt Wright Survived the Most Dangerous Discovery Channel Challenge Ever," 17 June 2018 The plague is a serious disease caused by bacteria often found in fleas, according to the Centers for Disease Control and Prevention (CDC). Sarah Jacoby, SELF, "A Child in Idaho Is Recovering From a Rare Human Case of the Plague," 15 June 2018 The data released Tuesday showed increases in several illnesses in 2017 that could have been linked to the storm: Cases of sepsis, a serious bloodstream infection usually caused by bacteria, rose from 708 in 2016 to 835 last year. Time, "Puerto Rico Has Released New Data Detailing Deaths in the Wake of Hurricane Maria," 14 June 2018 The data released Tuesday showed increases in several illnesses in 2017 that could have been linked to the storm: Cases of sepsis, a serious bloodstream infection usually caused by bacteria, rose from 708 in 2016 to 835 last year. NBC News, "Puerto Rico issues new data on Hurricane Maria deaths," 13 June 2018 The Geosmin’s earthy, musty taste and smell is produced by bacteria in soil and algae found on surface water, according to Stephen Pratt, Manager of Laboratory Services at the MDC. Mikaela Porter,, "Despite Taste And Odor, MDC Says Water In Area Towns Safe To Drink," 8 June 2018

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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Statistics for bacteria

Last Updated

18 Sep 2018

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Time Traveler for bacteria

The first known use of bacteria was in 1864

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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 \

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

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