Certified Ophthalmic Assistant Practice Exam

Which medium is commonly used to culture microorganisms?

1. Liquid broth

2. Potato dextrose agar

3. Agar

4. Gelatin

The correct answer is: Agar

Agar is a versatile and widely used medium for culturing microorganisms. It serves as a solidifying agent that provides a stable gel-like surface on which bacteria, fungi, and other microorganisms can grow. The composition of agar allows for easy manipulation when adding nutrients, antibiotics, or specific substances needed for the growth of different organisms. Liquid broth is also a medium used for culturing microorganisms, but it does not provide the solid substrate that agar does, which is essential for isolating colonies. Potato dextrose agar is a specific type of agar that is used primarily for fungi and yeast, but it is a subgroup of the broader category of agar media. Gelatin can also be used as a medium; however, it is less common in many laboratory settings compared to agar due to its tendency to melt at higher temperatures and its susceptibility to bacterial digestion. Thus, agar is recognized as the standard solid medium for microbial culture, favored for its effectiveness and the variety of formulations available.