bacterium

/bækˈtɪriəm/

/bækˈtiriəm/

Use the word bacterium when you're talking about a single-celled organism. Your uncle's bad case of pneumonia might be caused by a bacterium.

You're more likely to be familiar with the plural form of bacterium, bacteria. A bacterium is frequently the cause of diseases, specifically those known as bacterial illnesses. In biology, a bacterium is simply a microorganism, or a very tiny living thing, with cell walls but no distinct nucleus. The word itself comes from the Greek word bakterion, "small stick or rod," which describes a bacterium's shape when seen under a microscope.

Definitions of bacterium

1. noun

   (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 to be plants
   synonyms: bacteria

   types:

   acidophil, acidophile

   an organism that thrives in a relatively acid environment

   probiotic, probiotic bacterium, probiotic flora, probiotic microflora

   a beneficial bacterium found in the intestinal tract of healthy mammals; often considered to be a plant

   bacteroid

   a rodlike bacterium (especially any of the rod-shaped or branched bacteria in the root nodules of nitrogen-fixing plants)

   eubacteria, eubacterium, true bacteria

   a large group of bacteria having rigid cell walls; motile types have flagella

   Calymmatobacterium, genus Calymmatobacterium

   a genus of bacterial rods containing only the one species that causes granuloma inguinale

   Francisella, genus Francisella

   a genus of Gram-negative aerobic bacteria that occur as pathogens and parasite in many animals (including humans)

   Neisseria gonorrhoeae, gonococcus

   the pus-producing bacterium that causes gonorrhea

   Legionella pneumophilia, legionella

   the motile aerobic rod-shaped Gram-negative bacterium that thrives in central heating and air conditioning systems and can cause Legionnaires' disease

   nitrobacterium

   any of the bacteria in the soil that take part in the nitrogen cycle; they oxidize ammonium compounds into nitrites or oxidize nitrites into nitrates

   penicillin-resistant bacteria

   bacteria that are unaffected by penicillin

   pus-forming bacteria

   bacteria that produce pus

   rod

   any rod-shaped bacterium

   diplococcus

   Gram-positive bacteria usually occurring in pairs

   superbug

   a strain of bacteria that is resistant to all antibiotics

   B, bacillus

   aerobic rod-shaped spore-producing bacterium; often occurring in chainlike formations; found primarily in soil

   cocci, coccus

   any spherical or nearly spherical bacteria

   coccobacillus

   a bacterial cell intermediate in morphology between a coccus and a bacillus; a very short bacillus

   spirilla, spirillum

   any flagellated aerobic bacteria having a spirally twisted rodlike form

   clostridia, clostridium

   spindle-shaped bacterial cell especially one swollen at the center by an endospore

   Clostridium botulinum, botulinum, botulinus

   anaerobic bacterium producing botulin the toxin that causes botulism

   clostridium perfringens

   anaerobic Gram-positive rod bacterium that produces epsilon toxin; can be used as a bioweapon

   blue-green algae, cyanobacteria

   predominantly photosynthetic prokaryotic organisms containing a blue pigment in addition to chlorophyll; occur singly or in colonies in diverse habitats; important as phytoplankton

   phototrophic bacteria, phototropic bacteria

   green and purple bacteria; energy for growth is derived from sunlight; carbon is derived from carbon dioxide or organic carbon

   pseudomonad

   bacteria usually producing greenish fluorescent water-soluble pigment; some pathogenic for plants and animals

   xanthomonad

   bacteria producing yellow non-water-soluble pigments; some pathogenic for plants

   nitric bacteria, nitrobacteria

   soil bacteria that convert nitrites to nitrates

   nitrosobacteria, nitrous bacteria

   soil bacteria that oxidize ammonia to nitrites

   thiobacillus

   small rod-shaped bacteria living in sewage or soil and oxidizing sulfur

   spirillum

   spirally twisted elongate rodlike bacteria usually living in stagnant water

   vibrio, vibrion

   curved rodlike motile bacterium

   corynebacterium

   any species of the genus Corynebacterium

   listeria

   any species of the genus Listeria, a bacteria that can contaminate food and make people very sick

   enteric bacteria, enterics, enterobacteria, entric

   rod-shaped Gram-negative bacteria; most occur normally or pathogenically in intestines of humans and other animals

   endospore-forming bacteria

   a group of true bacteria

   rickettsia

   any of a group of very small rod-shaped bacteria that live in biting arthropods (as ticks and mites) and cause disease in vertebrate hosts; they cause typhus and other febrile diseases in human beings

   chlamydia

   coccoid rickettsia infesting birds and mammals; cause infections of eyes and lungs and genitourinary tract

   mycoplasma

   any of a group of small parasitic bacteria that lack cell walls and can survive without oxygen; can cause pneumonia and urinary tract infection

   nitrate bacterium, nitric bacterium

   any of the nitrobacteria that oxidize nitrites into nitrates

   nitrite bacterium, nitrous bacterium

   any of the nitrobacteria that oxidize ammonia into nitrites

   actinomycete

   any bacteria (some of which are pathogenic for humans and animals) belonging to the order Actinomycetales

   actinomyces

   soil-inhabiting saprophytes and disease-producing plant and animal parasites

   mycobacteria, mycobacterium

   rod-shaped bacteria some saprophytic or causing diseases

   streptobacillus

   any of various rod-shaped Gram-negative bacteria

   gliding bacteria, myxobacter, myxobacteria, myxobacterium, slime bacteria

   bacteria that form colonies in self-produced slime; inhabit moist soils or decaying plant matter or animal waste

   lactobacillus

   a Gram-positive rod-shaped bacterium that produces lactic acid (especially in milk)

   Lactobacillus acidophilus, acidophilus

   a bacterium that is used to make yogurt and to supplement probiotics

   Diplococcus pneumoniae, pneumococcus

   bacterium causing pneumonia in mice and humans

   strep, streptococci, streptococcus

   spherical Gram-positive bacteria occurring in pairs or chains; cause e.g. scarlet fever and tonsillitis

   spirochaete, spirochete

   parasitic or free-living bacteria; many pathogenic to humans and other animals

   type of:

   micro-organism, microorganism

   any living thing that is too small to be seen with the naked eye