If you think the smell has an organic source (smelly feet, urine, micro-organisms etc.) you might try one of the enzyme solutions available at pet stores which are made for getting urine and other pet odors out of carpeting and upholstery.

I don't if it will work in your case, but it probably can't hurt, other than the money it will cost.

Of course, something like unsalted meat tenderizer (enzyme based) might work just as well.