**Question:** Selective media for N. gonorrhoeae:

A. Chocolate agar with catalase test
B. MacConkey agar
C. Thayer-Martin agar
D. Blood agar

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

**Core Concept:** Selective media are specially prepared agar plates used for isolating and growing specific microorganisms while suppressing the growth of other microorganisms present in the sample.

**Why the Correct Answer is Right:** Thayer-Martin agar is a selective medium used for the isolation and cultivation of Neisseria gonorrhoeae, the bacterium responsible for gonorrhoea. It is particularly useful for isolating gonococci from clinical samples like vaginal swabs, urethral swabs, and cervical smears. The medium is designed to inhibit the growth of other common contaminants like Staphylococcus aureus and Escherichia coli while promoting the growth of N. gonorrhoeae.

**Why Each Wrong Option is Incorrect:**

A. Chocolate agar with catalase test: While chocolate agar is a rich medium that supports the growth of various bacteria, the catalase test is used to identify and differentiate between Neisseria species. However, it does not specifically select for N. gonorrhoeae.

B. MacConkey agar: MacConkey agar is a differential medium used for the differentiation between lactose-fermenting and non-lactose-fermenting bacteria. It does not specifically select for N. gonorrhoeae.

D. Blood agar: Blood agar is a rich medium used for the growth of aerobic Gram-positive and Gram-negative organisms. It does not specifically select for N. gonorrhoeae.

**Clinical Pearl:** Selective media are essential in microbiology for isolating and identifying specific microorganisms from complex microbial mixtures in clinical samples. Thayer-Martin agar is a widely used selective medium for the isolation of N. gonorrhoeae, ensuring accurate diagnosis and treatment of gonorrhoea infections.