Question

Which type of medium allows for the differentiation of microorganisms based on their metabolic characteristics?

• A. Defined medium
• B. Complex medium
• C. Selective medium
• D. Differential medium

Hint:

• Selective media: Favor the growth of particular microorganisms while inhibiting others. (e.g., media with antibiotics).
• Differential media: Distinguish between different groups of microorganisms based on visible characteristics (e.g., colony color, precipitation) due to their metabolic reactions. (e.g., MacConkey agar, Blood agar).
• Some media can be both selective and differential.
• Defined media have known compositions; complex media have some unknown components.

Answer 1

The Correct Option is D

Microbiological culture media can be classified based on their composition and purpose:

• Defined Medium (Synthetic Medium): All chemical components and their exact concentrations are known. Used when the precise nutritional requirements of an organism are known.
• Complex Medium (Undefined Medium): Contains at least one ingredient whose chemical composition is not precisely known (e.g., yeast extract, peptone, beef extract). Supports the growth of a wide variety of microorganisms.
• Selective Medium: Contains components that inhibit the growth of certain microorganisms while allowing others to grow. Used to isolate specific types of microbes from a mixed population.
• Differential Medium: Contains specific ingredients or indicators (e.g., pH indicators, substrates for specific enzymes) that allow microbiologists to distinguish between different types of microorganisms growing on the same plate based on visible differences in their growth (e.g., colony color, changes in the medium around colonies). These differences often reflect variations in metabolic characteristics, such as the ability to ferment a particular sugar or produce a specific enzyme.

For example, MacConkey agar is both selective (inhibits Gram-positive bacteria) and differential (differentiates lactose fermenters, which appear pink, from non-lactose fermenters, which appear colorless, based on acid production and a pH indicator). Therefore, a differential medium is designed to distinguish microorganisms based on their metabolic activities. \[ \boxed{\text{Differential medium}} \]