‘Leprosy’ is caused by

The correct option is Mycobacterium.

Leprosy, also known as Hansen's disease, is a chronic infectious disease primarily affecting the skin, peripheral nerves, mucosal surfaces of the upper respiratory tract, and the eyes. It is caused by the bacterium Mycobacterium leprae (and less commonly, Mycobacterium lepromatosis).

To understand why this is the correct answer, we can analyze the options provided:
1. Mycobacterium: The genus of actinobacteria that includes Mycobacterium leprae, the causative agent of leprosy. This matches the correct option.
2. Salmonella: A genus of rod-shaped Gram-negative bacteria that primarily causes illnesses like typhoid fever and food poisoning (salmonellosis), not leprosy.
3. TMV (Tobacco Mosaic Virus): A plant virus that infects a wide range of plants, especially tobacco, causing characteristic patterns (mottling and discoloration) on the leaves. It does not infect humans.
4. Monocystis: A genus of unicellular protozoan parasites that live in the seminal vesicles of earthworms, having no role in human diseases.

Therefore, leprosy is caused by the bacterium belonging to the genus Mycobacterium.