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The Collaborative International Dictionary

Bacterium \Bac*te"ri*um\ (b[a^]k*t[=e]"r[i^]*[u^]m), n.; pl. Bacteria (b[a^]k*t[=e]"r[i^]*[.a]). [NL., fr. Gr. bakth`rion, ba`ktron, a staff: cf. F. bact['e]rie.] (Biol.) A microscopic single-celled organism having no distinguishable nucleus, belonging to the kingdom Monera. Bacteria have varying shapes, usually taking the form of a jointed rodlike filament, or a small sphere, but also in certain cases having a branched form. Bacteria are destitute of chlorophyll, but in those members of the phylum Cyanophyta (the blue-green algae) other light-absorbing pigments are present. They are the smallest of microscopic organisms which have their own metabolic processes carried on within cell membranes, viruses being smaller but not capable of living freely. The bacteria are very widely diffused in nature, and multiply with marvelous rapidity, both by fission and by spores. Bacteria may require oxygen for their energy-producing metabolism, and these are called aerobes; or may multiply in the absence of oxygen, these forms being anaerobes. Certain species are active agents in fermentation, while others appear to be the cause of certain infectious diseases. The branch of science with studies bacteria is bacteriology, being a division of microbiology. See Bacillus.

Douglas Harper's Etymology Dictionary

c.1848, singular of bacteria (q.v.).


n. (context microbiology English) A single celled organism with cell walls but no nucleus or organelles.


n. (microbiology) single-celled or noncellular spherical or spiral or rod-shaped organisms lacking chlorophyll that reproduce by fission; important as pathogens and for biochemical properties; taxonomy is difficult; often considered plants [syn: bacteria]

Bacterium (genus)

The genus Bacterium was a taxon described in 1828 by Christian Gottfried Ehrenberg. The type species was later changed from Bacterium triloculare to Bacterium coli (now Escherichia coli) as it was lost. In 1951 and then in 1954 it was recognised as a nomen generum rejiciendum, which means a generic name to be rejected, this also applied to its family Bacteriaceae.

This genus included non-spore forming rods whose relation to other species was obscure (a "taxonomy dumping group"). This is different from the genus Bacillus, whose members were spore forming rods (sensu Cohn 1872).

Bacterium (disambiguation)

Bacterium may refer to:

  • Singular form of bacteria
  • Bacterium (genus)
  • Bacterium (film), a 2006 film

Usage examples of "bacterium".

Terrorists have used anthrax bacteria to infect, to kill, and to terrorize innocent people.

Our assumptions had been based principally on how the anthrax bacterium acted in settings that were almost preindustrial--before most buildings were air conditioned, before technology allowed us to sort mail with the force of air, and before we had advanced medical technologies to help us stabilize patients and make more definitive diagnoses.

If fitted correctly--and this is harder than it sounds--respirators can reduce exposure to anthrax bacteria and other harmful agents.

The anthrax bacterium grows naturally throughout the world, including the United States.

In the inhalational anthrax cases following September 11, the average time from exposure to the bacteria to the onset of symptoms was four days.

But experts believe that illness may occur as long as sixty days after exposure to anthrax spores, because observations have shown that the spores can take that long to change to active bacteria.

First, only certain strains of anthrax bacteria are exceptionally deadly.

Nor does smallpox have the ability to form spores, the hard shells that protect anthrax and botulism bacteria indefinitely in a state of suspended animation.

Like anthrax, the bacterium Clostridium botulinum forms a hard shell, called a spore, to protect itself when the environment turns inhospitable.

There are many parallels between the bacteria that cause anthrax and botulism: Both form spores and come naturally from the soil.

The antibody coating seemed to stiffen and tighten and the bacterium within writhed.

Once trapped in the node, the bacterium is handled by antibodies or, if that fails, by white cells mobilized for battle.

A bacterium, moving blindly through a cloud of hovering antibodies, seemed to attract them, to pull them in to itself.

In appearance they are not very different from conventional bacteria, but at high magnification, or rather, at a relatively high magnification, the highest magnification a conventional school microscope is capable of, if you look very carefully you could see some particles inside that have regular geometric shapes.

Some of the bacteria were marked with a felt pen circles, and inside those one could indeed see some rectangles and geometrically perfect spheres that were interconnected by some strings and pipes.