Phenylethanol agar (PEA) is a selective medium used to isolate gram-positive bacteria, especially staphylococci and streptococci. It contains the following components:

1. Base:

* Trypticase Soy Agar (TSA): Provides essential nutrients for bacterial growth.

2. Selective Agent:

* Phenylethanol: This is the key ingredient that inhibits the growth of most gram-negative bacteria. It does this by disrupting their cell membranes.

3. Other Ingredients:

* Sodium chloride: Provides electrolytes for bacterial growth.

* Agar: A solidifying agent.

Here's a typical recipe for Phenylethanol agar:

* Trypticase Soy Agar (TSA) - 38.5 g

* Phenylethanol - 2.5 g

* Sodium chloride - 2.5 g

* Distilled water - 1 liter

Preparation:

1. Suspend the ingredients in 1 liter of distilled water.

2. Heat the mixture gently while stirring until the agar dissolves completely.

3. Sterilize the medium in an autoclave at 121°C for 15 minutes.

4. Pour the sterile medium into petri dishes and allow them to solidify.

Note: Phenylethanol agar is often used in conjunction with other selective media, like blood agar, to enhance the isolation and identification of specific bacteria.