Cragie tube

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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.


  1. ^ Textbook of Microbiology by Prof. C P Baveja, ISBN 81-7855-266-3
  2. ^ Textbook of Microbiology by Ananthanarayan and Panikar, ISBN 81-250-2808-0

See also[edit]