## **Core Concept**
The question tests knowledge of microbiological media used for culturing specific bacteria, in this case, *Neisseria meningitidis*, the causative agent of meningococcal infections. Selective media are used to inhibit the growth of unwanted bacteria while allowing the growth of desired bacteria.

## **Why the Correct Answer is Right**
Thayer-Martin agar is a selective medium specifically designed for the isolation of *Neisseria meningitidis*. It contains antibiotics (like vancomycin, colistin, nystatin, and sometimes trimethoprim lactate) to inhibit the growth of other bacteria, and it is enriched with nutrients to support the growth of *N. meningitidis*. This medium takes advantage of the fact that *N. meningitidis* is relatively resistant to the antibiotics used.

## **Why Each Wrong Option is Incorrect**
* **Option A:** Chocolate agar is an enriched medium used for growing *Haemophilus* and *Neisseria* species but is not selective. It does not contain antibiotics to inhibit other bacteria.
* **Option B:** Blood agar is a non-selective, enriched medium that supports the growth of a wide range of bacteria. It does not inhibit the growth of unwanted bacteria.
* **Option D:** Sabouraud agar is a selective and differential medium primarily used for fungi, especially yeast and molds. It is not suitable for culturing *N. meningitidis*.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that for the isolation of *Neisseria meningitidis*, a specimen should ideally be taken from a sterile site, and the sample should be transported and processed rapidly, as the organism is sensitive to drying and temperature changes. Thayer-Martin agar is a critical tool in the microbiological diagnosis of meningococcal infections.

## **Correct Answer:** . Thayer-Martin agar