I had this recently and I believe it's due to the fact we don't wash as hot as we used therefore the water isn't getting hot enough to kill the bacteria.
I googled and got told to try a bottle of white vinegar poured in the soap drawer then put it on the hotest wash your machine will go. This didn't work for me.
Someone then told me to put half a tub of bircarbonate of soda in the soap dish and again, run an empty machine on the hottest wash you can (I did 90deg wash) and this did the trick. I've also been told that if I do a very hot wash every few weeks say, with tea towels or something, this should be enough to keep the smells at bay.
Hope this helps.
Dianne
May 2011