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MacConkey Agar is a specialized growth medium commonly used in microbiology laboratories to cultivate and differentiate gram-negative bacteria. It contains specific indicators that distinguish between lactose fermenters and non-fermenters. In this guide, we will walk you through the preparation of MacConkey Agar as per the protocols used at Heredity Biosciences Student Laboratory.

Materials Required:

1. MacConkey Agar powder
2. Distilled water
3. Conical flask
4. Autoclave
5. pH meter
6. Measuring cylinder
7. Stirring rod
8. Bunsen burner
9. Petri dishes

Procedure:

1. Weighing the MacConkey Agar Powder:
   • Start by weighing the appropriate amount of MacConkey Agar powder according to the manufacturer’s instructions. The typical ratio is 54 grams of MacConkey Agar powder per liter of distilled water. Adjust the quantity as needed.
2. Mixing with Distilled Water:
   • Pour the measured MacConkey Agar powder into a clean conical flask.
   • Add distilled water in the required volume (typically 1 liter for 54 grams of MacConkey Agar powder). The water should be at room temperature.
   • Stir the mixture using a sterile stirring rod until the powder is completely dissolved in the water.
3. Adjusting pH:
   • Use a pH meter to check the pH level of the solution. The optimal pH for MacConkey Agar is around 7.1.
   • If the pH is not within the desired range, adjust it by adding small amounts of 1N sodium hydroxide (NaOH) or 1N hydrochloric acid (HCl) as needed.
4. Autoclaving:
   • Pour the prepared MacConkey Agar solution into appropriate containers, such as conical flasks or bottles.
   • Cover the containers with aluminum foil or cotton plugs.
   • Autoclave the containers at 121°C for 15 minutes to sterilize the agar medium. Ensure that the pressure and temperature are suitable for sterilization.
5. Cooling and Pouring Agar Plates:
   • After autoclaving, allow the MacConkey Agar solution to cool to approximately 45-50°C. It should still be in a liquid state.
   • Pour the sterile MacConkey Agar into sterile Petri dishes to create agar plates. It’s crucial to maintain aseptic conditions during this step.
6. Solidification:
   • Let the poured agar plates sit undisturbed until they solidify at room temperature.
7. Storage:
   • Store the prepared MacConkey Agar plates in a refrigerator or at a temperature suitable for maintaining their integrity until they are ready for use.

Note: It’s essential to follow aseptic techniques throughout the preparation process to prevent contamination of the medium.

By preparing MacConkey Agar following these protocols, students at Heredity Biosciences can conduct experiments and studies in microbiology, contributing to their understanding of bacterial growth and differentiation.

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