How do I kill mold in my car?

I don't know if it was there when I bought the car last august, or if my husband lied about spilling something when he borrowed it for an out of state trip a couple months after. It is on the floor in the back seat right under where the floor mat goes. I keep cleaning it, but it keeps coming back and it is making my car smell like mildew!!!!! It just keeps coming back. I don't put the floor mat on it. I try to let it air out as much as I can after cleaning, but it rains a lot here and I don't have a garage. Everyone keeps telling me to put bleach onit, but that will bleach the carpet! Or tear up the carpet and put bleach underneath. Ya cuz that's not gonna ruin it..... Please help!