Procedure for Preparation of Selective and Differential Medium

Now prepare the MacConkey agar medium following the steps given herewith:

1. Weigh and dissolve all ingredients except agar one by one in 500 ml of distilled water.

2. Make the volume to 1000 ml with distilled water and set the pH to 7.3.

3. Add agar and dissolve it by heating.

4. Autoclave the medium at 15 psi for 15-20 minutes.

5. After cooling to 45^oC, dispense the medium aseptically into sterile petri plates.

6. Allow to solidify and then inoculate with the given cultures.

For inoculation, divide the plate into different sections by marking the bottom of the dish. Label each section with the name of the organism to be inoculated. Inoculate the plate with different organisms by making a single line of inoculation of each organism at appropriate section/place as shown in margin Figure.

7. Incubate the plates in inverted position for 24 hours at 37^oC and then record observations.