Explain the Procedure for Preparation of Culture Media?

Now carry out the exercise following the steps given herewith:

1. To prepare potato dextrose medium, first, peel off and chop 200 gms of potato tubers and then boil in a beaker containing 500 ml of distilled water for 20 minutes.

2. Filter the potato extract with muslin cloth and collect the filtrate.

3. Mix potato extract with other ingredients, i.e., peptone and dextrose and make the volume 1000 ml by distilled water. Adjust the pH by adding 1 N NaOH / 1 N HCl drop-wise.

4. Add 15 gm of agar and dissolve it by heating.  Finally,  pour it into 3 or 4 Erlenmeyer flasks of 500 ml capacity.  Close the mouth of flasks by cotton plugs and then cover it with brown paper or aluminium foil.

5. Sterilize the medium by autoclaving at 15 psi for 15-20 minutes.

6. When the medium cools to 45-50°C, pour it in sterile petri plates for agar plates and in sterile test tubes for slants. Allow it to solidify.

7. For point inoculation, hold the inoculating needle in right hand and sterilize it red hot by keeping it in bunsen burner.

8. Hold the culture tube in left hand and take out the cotton plug with little finger of right hand. Sterilize the mouth of the tube by passing through the flame. Take out the small quantity of the inoculum with sterile inoculating needle after cooling it by touching to the uninoculated medium.

9. Handle the PDA plate in left hand and open the petri plate slightly with the help of thumb. Inoculate it at one point in the centre of the medium. Close the lid and keep the plate for incubation at 28 ± 2°C. Repeat the process for other fungal cultures. Observe after 3-5 days.