Question

Mac-Conkey medium is an example of

• A. Transport medium
• B. Enrichment medium
• C. Differential medium
• D. Selective Medium

Hint:

Mac-Conkey medium is used to differentiate Gram-negative bacteria based on their ability to ferment lactose, which changes the color of the medium.

Answer 1

The Correct Option is C

Mac-Conkey medium contains lactose along with neutral red as a pH indicator, so lactose-fermenting bacteria produce acidic byproducts that turn their colonies pink to red, while non-fermenters remain pale or colorless. This visible distinction between colony types based on a biochemical property is what defines a differential medium, which is the classification being tested in this question, separate from its additional (but secondary, in this context) selective properties from bile salts and crystal violet.

Therefore, the correct answer is Differential medium.

Answer 2

Another way to approach this is to focus specifically on what changes are observed on the plate itself, rather than which organisms are permitted to grow.

1. Transport medium: This classification concerns keeping a specimen viable during transport, a purpose unrelated to what is observed on a Mac-Conkey plate.
2. Enrichment medium: This classification concerns boosting the numbers of a target organism in a liquid culture before it is even plated, which is a different step from what Mac-Conkey medium is used for.
3. Differential medium: Since colonies on Mac-Conkey medium change color based on lactose fermentation, allowing different bacterial types to be visually told apart on the same plate, this matches the classification being tested.
4. Selective Medium: While true that certain organisms are inhibited on this medium, the question is emphasizing the ability to tell colony types apart by appearance, which is the differential function specifically.

Focusing on the visual colony differences rather than growth inhibition points to the differential classification.

Therefore, the correct answer is Differential medium.