First dry everything thoroughly.
Then as Auggie suggested. Bleach, bleach and more bleach. You have to kill the lingering mold spores.
If the problem keeps on recurring, you may want to consider re-painting the bathroom with mildew-resistant paint.
Another thing to get in the habit of doing is opening the bathroom window(s) for awhile after showering to allow adequate drying out. Dampness is the friend of mold.