Siderophores are bacterial proteins that compete with the host's:

a. iron-transport proteins.

b. antibodies.

c. red blood cells.

d. white blood cells.

e. receptors.

a. iron-transport proteins.

Explanation:

The bacteria require iron for the growth where iron acts as a cofactor of various enzymes, as an integral part of various structures.

The bacteria when facing low iron in them, they produce some low molecular weight molecule called chelators which are known to bring the iron of the host by competing with the iron transport proteins.

These chelators are known as the siderophores which show high affinity for the ferric ionic state of iron.

Thus, option-A is correct.