Cragie tube

The Cragie tube or Craigie tube is a method used in microbiology^[1][2] for determining bacterial motility.

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.

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.

• Kauffman-White classification

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