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bacteriochlorophyll
bacteriol.
bacteriology
bacteriolysis
bacteriophage
bacterioplankton
bacteriostasis
bacteriostat
bacterium
bacteriuria
Bactria
Bactrian camel
baculiform
bad
bad actor
bad apple
bad blood
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bacterium

bac·te·ri·um [ bak tree əm ] (plural bac·te·ri·a [ bak tree ə ])


noun 
Definition:
 
microscopic life form: a single-celled, often parasitic microorganism without distinct nuclei or organized cell structures. Various species are responsible for decay, fermentation, nitrogen fixation, and many plant and animal diseases. Kingdom Eubacteria.

[Mid-19th century. < Greek baktērion "little rod" (because the first ones discovered were rod-shaped) < baktron "rod"]

bac·te·roid [ báktə ròyd ] adjective

Word Usage
bacterium or bacteria?

Bacterium is singular and bacteria is plural. The word is more commonly found in the plural, which can lead to its being wrongly treated as a singular noun taking a singular verb.

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