This is a two part process and you'll want to be sure and do both to get rid of all of the smell. The solution - a pair of my favorites: Baking soda and white vinegar.
The first thing you want to do is to wash the towels in hot water adding 2 cups of white vinegar to the wash cycle.
The vinegar does two things, one it kills the bacteria and second it strips away detergent and fabric softener build-up from the towels.
Next, run the towels through a second hot wash cycle. This time add a cup of baking soda to the wash cycle.
The baking soda absorbs odors and softens the fabric so that the towels come out fluffy and soft and odor free!!
An easy solution to a stinky problem! I'm Mrs. Fixit and it's just that simple!