what can a bacterium do to respond to high levels of transferrin?

Answer 1

They can secrete siderophores that capture iron, and can then be transported back inside the bacteria.

Here's a link to an article about the battle between bacteria and host organism for iron.

Answer 2

I'm not sure the question makes sense. Transferrin is the iron transport protein in mammals. High levels of transferrin arent toxic to bacteria. High levels of iron, however, can stimulate bacterial growth. If the bacteria could denature transferrin and release the bound iron, bacterial growth and survival would be enhanced.