bacterium[bak tir′ē əm]
- Any of various prokaryotic microorganisms of the domain Bacteria that may be free-living, saprophytic, commensal, or pathogenic and that vary widely in terms of morphology, oxygen tolerance, nutritional and temperature requirements, and motility. Also called eubacterium.
- Any of the prokaryotic organisms, such as an archaeon. Not in scientific use.
Origin of bacteriumNew Latin bactērium, from Greek baktērion, diminutive of baktron, rod; see bak- in Indo-European roots.
top: rod-shaped bacterium
bottom: spiral-shaped bacterium
- 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 incorrect.
Variant of bacteria
plural nounsing. bacterium or bacteria
Origin of bacteriaModern Latin plural of bacterium ; from Classical Greek baktērion, diminutive of baktron, a staff: see bacillus