**Core Concept**
Selective media for Mycobacterium refers to specialized growth mediums that allow the isolation and cultivation of these bacteria while inhibiting the growth of other microorganisms. This is crucial for laboratory diagnosis of mycobacterial infections, such as tuberculosis.

**Why the Correct Answer is Right**
The correct answer is based on the use of a medium that contains a specific ingredient which inhibits the growth of competing bacteria. Mycobacteria require a nutrient-poor environment to grow, making it ideal to use a medium that restricts the growth of other microorganisms. Löwenstein-Jensen medium is a classic example of selective media for mycobacteria, which contains ingredients like glycerol, asparagine, and pyruvate. The medium's pH is also adjusted to favor the growth of mycobacteria.

**Why Each Wrong Option is Incorrect**
* **Option A:** MacConkey agar is a selective medium for gram-negative bacteria, particularly enteric pathogens, and is not suitable for mycobacteria.
* **Option B:** Blood agar is a general-purpose medium that supports the growth of a wide range of bacteria, including mycobacteria, but it does not provide the selective conditions required for isolation.
* **Option C:** Sabouraud dextrose agar is a medium used for the cultivation of fungi, not mycobacteria.

**Clinical Pearl / High-Yield Fact**
Remember that mycobacteria require a longer incubation period (typically 4-6 weeks) compared to other bacteria, which is why selective media are essential for their isolation and cultivation.

**Correct Answer:** C. Sabouraud dextrose agar is not used for mycobacteria.