Well, I sure hate to give up my sponges, but....(from a recent health article)

A sponge is like the back row in study hall -- it attracts all the bad elements. So here’s what you should do with it:
Toss it, suggest YOU docs Mehmet Oz, MD, and Michael Roizen, MD. Instead, buy 10 cheap dishcloths and 2 buckets. Put the clean cloths in one bucket and the dirty cloths in the other bucket along with some diluted bleach. Wash all the cloths once a week.

More Sanitary Solutions
Sponges actually grow bacteria. But if you simply can’t part with your sponges, run them through the dishwasher once a week. You can also microwave damp sponges for a minute to kill germs. But use extreme caution: Wet the sponge thoroughly, and use tongs to take it out of the microwave. (Find out why your faucet beats hand wipes.)