Flavobacterium columnare is a thin Gram-negative

Gram-negative

Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...

 rod bacterium of the genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Flavobacterium

Flavobacterium

Flavobacterium is a genus of Gram-negative, non-motile and motile, rod-shaped bacteria that consists of ten recognized species, as well as three newly proposed species . Flavobacteria are found in soil and fresh water in a variety of environments...

. The name derives from the way in which the organism grows in rhizoid

Rhizoid

Rhizoids are thread-like growths from the base or bottom of a plant, found mainly in lower groups such as algae, fungi, bryophytes and pteridophytes, that function like roots of higher plants ....

 columnar formations.

The species was first described by Davis (1922), and the name was validated by Bernardet and Grimont (1989).

F. columnare can be identified in the laboratory by a five-step method that demonstrates:

1. the ability to grow on a medium containing neomycin
   Neomycin
   Neomycin is an aminoglycoside antibiotic that is found in many topical medications such as creams, ointments, and eyedrops. The discovery of Neomycin dates back to 1949. It was discovered in the lab of Selman Waksman, who was later awarded the Nobel Prize in Physiology and medicine in 1951...
   
    and polymyxin B
   Polymyxin B
   Polymyxin B is an antibiotic primarily used for resistant gram-negative infections. It is derived from the bacterium Bacillus polymyxa. Polymyxin B is a mixture of two closely related compounds, polymyxin B1 and polymyxin B2. It has a bactericidal action against almost all gram-negative bacilli...
   
   ;
2. production of yellow pigmented rhizoid (root-like in appearance) colonies;
3. production of a gelatin-degrading enzyme
   Enzyme
   Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
   
   ;
4. binding of Congo red dye to the colony; and
5. production of a chondroitin
   Chondroitin
   Chondroitin is a chondrin derivative.Types include:* Chondroitin sulfate* Dermatan sulfate...
   
    sulfate-degrading enzyme.

The species has been known previously as Flexibacter columnaris, Bacillus columnaris, and Cytophaga columnaris.

F. columnare is one of the oldest known diseases among warm water fish, and manifests itself as an infection commonly known as Columnaris

Columnaris

Columnaris is a symptom of disease in fish which results from an infection caused by the gram negative, aerobic, rod shaped bacterium Flavobacterium columnare. It was previously known by the names of bacillus columnaris, chondrococcus columnaris, cytophaga columnaris and flexibacter columnaris...

. Infections are the second leading cause of mortality in pond raised catfish

Catfish

Catfishes are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores...

in the southeastern United States.