Demonstration of Bacterial Motility by Stab culture Method

Stab culture method is an indirect way to demonstrate bacterial true motility.  In this method, semisolid agar is used to cultivate the bacteria which allow the movement of the organisms in the medium.

Aim

To demonstrate the bacterial motility by Stab culture method.

Principle

Semisolid nutrient agar is poured into a test tube and allowed to set by keeping in upright position. Broth culture of organism is inoculated to the media by stabbing the culture.  If the organism is motile, it moves through the media and shows growth on the different parts of the media in addition to the line of stab. If non motile, growth can be seen only in the stabbed region of the tube.

Requirements

24 hr culture of E. coli and Staphylococcus spp.

Test tubes, Bunsen burner, straight inoculation needle etc.

Procedure

Prepare nutrient agar with 0.2 % agar concentration, heat to dissolve.

Pour agar approximately up to 10 mm height of the test tubes.

Put the cotton plug and sterilize the medium at 121^o C for 15 min. After sterilization, allow the medium to set in the upright position.

Inoculate the given microorganisms into the agar by stab method with the inoculation needle.

Incubate the tubes at 37^o C for 24 hrs.

Observations

E. coli showed growth throughout the inoculated medium, indicating that the organism is motile.  Staphylococcus sp. showed growth only in the stabbed region of the medium, indicating that it is non motile.

  

Result

In the given cultures, E. coli is motile which showed true motility and Staphylococcus sp. is non motile.