bacterium
/bakˈtɪərɪəm
/- The pneumococcal bacterium is the second most common cause of bacterial meningitis.
- Typhoid fever is a serious infection caused by the bacterium Salmonella typhi.
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, as they grow easily and reproduce rapidly in laboratory cultures.
Usage
Bacteria is the plural form (derived from Latin) of bacterium. Like any other plural it should be used with the plural form of the verb: the bacteria causing salmonella are killed by thorough cooking, not the bacteria causing salmonella is killed by thorough cooking. However, the unfamiliarity of the form means that bacteria is sometimes mistakenly treated as a singular form, as in the example above.
Origin
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.