Cragie tube

The Cragie tube or Craigie tube is a method used in microbiology for determining bacterial motility.

Technique

A hollow tube with some culture medium is placed in semi-solid agar inside a bottle. A sample of the bacterium to be tested is inoculated into the medium in the hollow tube and the setup is incubated at 37°C overnight.

Observation

On examining the areas where bacterial growth has occurred there are several observations to be made:

• the colonies of the non-motile bacteria remain confined within the tube at the site of inoculation
• the motile bacteria swim out from the bottom of the tube and colonize the surrounding medium as well

Confirmation may be obtained by subculture and retesting.

See also

• Kauffman-White classification