**Question:** Least chances of infective endocarditis is associated with:-

A. Prosthetic valves
B. Healthy individuals
C. Mitral valve
D. Transthoracic echocardiography

**Core Concept:**
Infective endocarditis (IE) is an infection of the cardiac valves or endocardial surface. The infection can be caused by bacteria, fungi, or viruses. Risk factors for developing IE include:
1. Valvular abnormalities (e.g., congenital heart disease, prosthetic valves)
2. Immunosuppression
3. Previous IE or other heart disease
4. Central venous catheterization or other invasive procedures
5. Drug addiction or intravenous drug use
6. Age over 60 years

**Why the Correct Answer is Right:**
The correct answer is **A. Prosthetic valves**.
Prosthetic valves are at higher risk for IE due to the foreign surface, which facilitates bacterial adhesion and colonization. The bacteria can then invade the valve tissue and grow, leading to IE. In comparison, healthy individuals have a lower risk because their immune systems are better equipped to fight off infections.

**Why Each Wrong Option is Incorrect:**

**Option B. Healthy individuals:**
This option is incorrect because despite having a healthy heart, an individual can still develop IE due to other risk factors such as intravenous drug use, central venous catheterization, or invasive procedures. Healthy individuals might also have a genetic predisposition to IE.

**Option C. Mitral valve:**
This option is incorrect because the risk of IE depends on the presence of underlying heart disease, not the valve itself. Mitral valve may be involved in IE, but other valves (e.g., aortic, tricuspid) can also be affected.

**Option D. Transthoracic echocardiography:**
This option is incorrect because an imaging test like transthoracic echocardiography is used to diagnose IE, not determine its risk. Risk factors and presence of valvular abnormalities are the main determinants of IE risk.

**Clinical Pearl:**
Prosthetic valves are a significant risk factor for infective endocarditis due to the foreign surface that allows bacteria to adhere and colonize. Even healthy individuals can develop IE through other risk factors or predisposing conditions. The risk is not solely determined by the valve itself but by the presence of underlying heart disease, invasive procedures, and other risk factors.