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Syllabification: bac·te·ri·um
Pronunciation: /ˌbakˈtirēəm

Definition of bacterium in English:

noun (plural bacteria /-ˈti(ə)rēə/)

A member of a large group of unicellular microorganisms that have cell walls but lack organelles and an organized nucleus, including some that can cause disease.

Bacteria are widely distributed in soil, water, and air, and on or in the tissues of plants and animals. Formerly included in the plant kingdom, they are now classified separately (as prokaryotes). They play a vital role in global ecology, as the chemical changes they bring about include those of organic decay and nitrogen fixation. Much modern biochemical knowledge has been gained from the study of bacteria because they grow easily and reproduce rapidly in laboratory cultures

Example sentences
  • A urine test can also be used to confirm that the bacteria are the Legionella bacteria.
  • The pneumococcal bacterium is the second most common cause of bacterial meningitis.
  • Typhoid fever is a serious infection caused by the bacterium Salmonella typhi.


mid 19th century: modern Latin, from Greek baktērion, diminutive of baktēria 'staff, cane' (because the first ones to be discovered were rod-shaped). Compare with bacillus.

  • This modern Latin term is formed from Greek baktērion ‘little staff’; the first bacteria to be discovered were rod-shaped. The word bacillus (late 19th century), a pathogenic bacterium, also meant ‘little rod’ in late Latin. Bacillus is also behind the French word debacle, adopted into English in the early 19th century. It literally means an unbarring and was first used of the breaking of ice or other blockage in a river and its effects, and then transferred to human behaviour.



Pronunciation: /-ˈti(ə)rēəl/
Example sentences
  • Nevertheless, some viable bacterial cells and bacterial and fungal spores are present.
  • Vaccines are made from killed bacteria, detoxified bacterial toxins, or modified viruses.
  • Some illnesses, such as ear infections and diarrhoea, may be either bacterial or viral.

Definition of bacterium in:

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