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TX (TA, TM, TG) Plates


2-3-5-triphenyl tetrazolium chloride (TTC) is a dye which turns red when reduced. Bacterial colonies that are expressing a certain biochemical activity can be identified by visual examination because they have a unique color on media containing a particular dye. In most cases the dye changes color when it is hydrolysed, or acts as a pH or redox indicator. TA (Tetrazolium Arabinose) are the most common plates used in this laboratory. We use TA agar for distinguishing Ara- and Ara+ strains in most competition assays. Colonies of Ara- strains typically appear red on TA agar, while those of Ara+ strains appear white/pink.

TX Agar

INGREDIENT1000 mL Flask2000 mL flask2000 mL flask
Total volume of media500 mL1000 mL1500 mL flask
Tryptone5 g10 g15 g
Yeast Extract0.5 g1 g1.5 g
Sodium Chloride2.5 g5 g7.5 g
Agar8 g16 g24 g
Distilled water400 mL800 mL1200 mL

TX Sugar

INGREDIENT250 mL Flask250 mL flask500 mL flask
Total volume of media500 mL1000 mL1500 mL flask
Sugar*5 g10 g15 g
Distilled water100 mL200 mL300 mL

*Sugar can be Arabinose (TA), Maltose (TM) or Glucose (TG).

  1. Prepare media in desired volumes.
  2. Carefully add a stir bar to flask and mix ingredients. Leave stir bar in while autoclaving.
  3. Autoclave on a liquid load for at least 45 minutes.
  4. After autoclaving, let cool to about 55°C (you should be able to place the back of your hand against the flask for a few seconds without it feeling too hot), add the arabinose and 1mL of sterile 5% TTC per liter of media and pour plates. Note: Plates should be poured immediately although agar can temporarily be stored in the 55°C oven. This should be avoided if possible due to potential bacterial contamination.
  5. Pour the plates.
  6. Allow Petri dishes to solidify for ~24 hours on the bench top before storing in the walk-in fridge. Cover the solidifying Petri dishes with a box or black garbage bag because TTC is light-sensitive.

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Original Recipe by: C. Eshelman Date: 26 July 12

Recipe Updated by: ___ Date: ___

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Page last modified on September 13, 2012, at 09:32 PM