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

Step 1: Understanding Mac-Conkey medium.
Mac-Conkey medium is both selective and differential. It is selective for Gram-negative bacteria and differentiates bacteria based on their ability to ferment lactose, turning the medium from yellow to red.
Step 2: Analyzing the options.
(1) Transport medium: Incorrect, Mac-Conkey medium is not used for transporting samples.
(2) Enrichment medium: Incorrect, Mac-Conkey medium is not an enrichment medium.
(3) Differential medium: Correct — Mac-Conkey medium is a differential medium, differentiating bacteria based on lactose fermentation.
(4) Selective Medium: Incorrect, although it has selective properties, it is not primarily classified as a selective medium.
Step 3: Conclusion.
Mac-Conkey medium is best described as a (3) Differential medium.

Answer 2

Microbiological culture media are classified by their intended function. Let's check each classification against what Mac-Conkey medium is used for.

1. Transport medium: Transport media are designed to preserve specimen viability during transit to a laboratory, which is not the purpose of Mac-Conkey medium.
2. Enrichment medium: Enrichment media are liquid formulations designed to boost the growth of a particular organism from a mixed sample before plating, which does not describe Mac-Conkey medium's solid-plate function.
3. Differential medium: Mac-Conkey medium contains lactose and a pH indicator, causing lactose-fermenting bacteria to produce visibly different (pink/red) colonies compared to non-fermenters (colorless), which is the defining feature of a differential medium.
4. Selective Medium: Mac-Conkey medium does contain bile salts and crystal violet that inhibit Gram-positive organisms, but the feature this question is testing is its ability to visually distinguish colony types, which is the differential property rather than the selective one.

The lactose-fermentation-based color differentiation is the property being tested here, pointing to the differential classification.

Therefore, the correct answer is Differential medium.