 If you're wondering why is mold forming there, it's because mold will grow on dust. And it's also an area where you get a lot of dust that sticks to the bottom of the refrigerator and sticks to the baseboard. So if you had the dust, which is sort of the mold food, and you had the moisture, that's what's going on there. You don't necessarily need to have a leak to get mold to grow. But what I would do is I'd pull the refrigerator out. I'd spray that area, saturate it with a 50-50 mix of bleach and water.