Who is responsible for bathtub caulk replacement?

[Chetan C.]

Hi folks,

Who is responsible for removing mold from the caulking around the bathtub when the tenant is leaving after a 1-year lease? This was when it was provided in good condition during move in? I had mentioned it to the tenant twice during the 2 walk throughs and they didn't fix it. The contract is charged $300 to remove the old caulk and apply new. 

Chetan