**Question:** Tellurite stimulates growth of

A. Bacteria
B. Fungi
C. Protozoa
D. Viruses

**Correct Answer:** D. Viruses

**Core Concept:** Tellurite is an inorganic compound with antimicrobial properties. It is toxic to bacteria, fungi, and some viruses. In medicine, tellurite is used to selectively inhibit the growth of certain bacteria in culture media, allowing the growth of other microorganisms, primarily viruses.

**Why the Correct Answer is Right:** Tellurite exerts its antimicrobial activity primarily through inhibiting the enzyme ribonuclease, which is essential for the synthesis of RNA in bacteria, fungi, and some viruses. By inhibiting ribonuclease, tellurite interferes with the vital processes of these microorganisms, leading to their growth inhibition. In contrast, tellurite does not directly affect the RNA synthesis in viruses, allowing them to grow, despite the presence of tellurite in the culture media.

**Why Each Wrong Option is Incorrect:**

**A. Bacteria:** Bacteria are indeed inhibited by tellurite due to its effect on ribonuclease. However, the question asks for the microorganism that Tellurite stimulates growth of, not inhibits.

**B. Fungi:** Similar to bacteria, fungi have ribonuclease, which is inhibited by tellurite. However, the question specifically asks for the growth stimulant.

**C. Protozoa:** Protozoa are eukaryotic microorganisms that can also have ribonuclease, which is inhibited by tellurite. However, the question asks for the growth stimulant, not inhibitor.

**D. Viruses:** As mentioned earlier, viruses do not have their own ribonucleases and can grow in the presence of tellurite due to its lack of direct effect on their RNA synthesis.

**Clinical Pearl:** Tellurite is often used in virology research to study viral replication and pathogenesis, as well as to isolate and purify viruses.

**Explanation:** Tellurite is a useful tool in virology research, as it allows for selective growth of viruses while inhibiting the growth of bacteria, fungi, and protozoa. By understanding these principles, students can effectively utilize tellurite in virology studies and differentiate between viruses and other microorganisms in culture media.