by Karly Forker
Fun Rating: 3/5
Difficulty Rating: 1/5
What is the general purpose?
Solid media plates provide a nutrient-dense surface that supports bacterial growth. Scientists use these plates to separate different types of bacteria and study them in the lab. Often scientists can separate bacteria by using a certain antibiotic to kill bacteria they are not interested in.
Why do we use it?
Solid media helps scientists grow bacteria in a controlled way, making them easier to study. Scientists can collect samples from patients and culture bacteria on plates to test for illness-causing bacteria, research antibiotic resistance, or continue researching bacteria in future experiments. Solid media also provides a carbon and nitrogen source necessary for bacteria to grow and reproduce.
Figure 1. Making solid media plates. Image created by author in BioRender.
How does it work?
Mixing the ingredients
Making solid media is like following a recipe for baking a cake. First you mix the ingredients. Just as there are different flavors of cake, there are different types of solid media, all of which have a different ratio of ingredients. The main components in solid media are salts for cell signaling and protein function, vitamins for metabolism and growth and other nutrients for energy and other cellular processes. Next, you add agar, which allows the mixture to turn into a Jello-O-like substance when heated. All ingredients are dissolved in water.
Sterilization
After dissolving the ingredients, the plates must be kept free from contaminants. To sterilize the media, it is placed in a special high-pressure oven called an autoclave. After autoclaving, the media should be free of germs.
Pouring the plates
Once the media is out of the autoclave and has cooled slightly, it is poured into petri dishes and allowed to harden to the Jello-like thickness. Sometimes, antibiotics are added to select for a certain type of bacteria.
Drying and storage
The plates are typically allowed to cool and set overnight. The next day, they are placed upside down in the fridge to prevent moisture build-up or contamination. Now your plates are ready for use!
