I have found if the surfaces can handle it. Almost all bathroom tiles can. You can use straight chlorine bleach in a sprayer with caution. (bleach can be very harsh read labeling on bottle) and spray on the mold or mildew. Let this set for about two or three minutes and then thoroughly rinse. If it is indeed mold it should kill it and loosen it so regular cleaning methods should remove it. (Scotch bright, or green back of kitchen sponges work well but make sure it doesn't damage you finish).