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3D diagram of a bacterium
Shapes of bacteria


From New Latin bactērium, from Ancient Greek βακτήριον (baktḗrion, small staff), from βακτηρία (baktēría).


  • IPA(key): /bækˈtɪəɹ.ɪəm/
  • (file)
  • Rhymes: -ɪəɹiəm


bacterium (plural bacteria or (uncommon, possibly nonstandard) bacteriums)

  1. (microbiology) A single-celled organism with cell walls but no nucleus or organelles.
    • 2013 July 20, “Welcome to the plastisphere”, in The Economist, volume 408, number 8845:
      Plastics are energy-rich substances, which is why many of them burn so readily. Any organism that could unlock and use that energy would do well in the Anthropocene. Terrestrial bacteria and fungi which can manage this trick are already familiar to experts in the field.

Usage notes[edit]

  • In most formal writing, bacterium is the singular form of the noun, and bacteria the plural form. This is in accord with the word's Latin etymology. However, in ordinary speech, some speakers use bacteria as a singular, with plural either bacteria or bacterias. This is usually considered nonstandard.



Derived terms[edit]


The translations below need to be checked and inserted above into the appropriate translation tables. See instructions at Wiktionary:Entry layout § Translations.

Further reading[edit]

See also[edit]


Latin Wikipedia has an article on:
Wikipedia la

Alternative forms[edit]


From Ancient Greek βακτήριον (baktḗrion, small staff), from βακτηρία (baktēría).



bactērium n (genitive bactēriī); second declension

  1. (Late Latin, Medieval Latin) cane, walking-stick; staff (of a shepherd)
  2. (New Latin, microbiology) bacterium


Second-declension noun (neuter).

Case Singular Plural
Nominative bactērium bactēria
Genitive bactēriī bactēriōrum
Dative bactēriō bactēriīs
Accusative bactērium bactēria
Ablative bactēriō bactēriīs
Vocative bactērium bactēria


  • bacterium in Charles du Fresne du Cange’s Glossarium Mediæ et Infimæ Latinitatis (augmented edition with additions by D. P. Carpenterius, Adelungius and others, edited by Léopold Favre, 1883–1887)
  • bacterium in Gaffiot, Félix (1934) Dictionnaire illustré latin-français, Hachette
  • bacterium in Bayerische Akademie der Wissenschaften (1967– ) Mittellateinisches Wörterbuch, Munich: C.H. Beck
  • Niermeyer, Jan Frederik (1976), “bacterius”, in Mediae Latinitatis Lexicon Minus, Leiden, Boston: E. J. Brill, page 76