What Causes Foul Smell From Infection On Foot In A Diabetic Patient?

I have been tending to my husbands diabetic foot for a couple of weeks under the VA and wound care. During tonights dressing change, I noticed a fowl smell. also, pai n. Should we go to the ER tomorrow? Could this be gangrene? WOW!! I guess nothing is for free. You should say that right up front!! Never mind. We ve got this.