Does a microwave kill germs, e.g. on a kitchen sponge?
Would it matter if it were wet or dry?
I asked my microbiology professor a similar question once, and he told me that you would have to nuke it for quite awhile. The microwaves themselves are not going to do much immediate damage to the little critters, but if you nuke it long enough, you will cause the water in them to boil, thus killing them. As to if it is better for the sponge to be wet or dry? I don’t know.
If you are worried about keeping your sponge clean, soak it in a mild bleach solution overnight.
I have absolutely no backing for what I’m about to say, but I’ma gonna say it anyway.
I wash my sponges in the dishwasher. I tried nuking them, but found that I had to leave them in too long in order to get it hot enough all the way through.
I do, however, put my dishrags in the microwave for a minute or two. I soak them and lay them flat, which also helps clean the bottom of the microwave.
I regularly put the sponges in the microwave (wet of course!). I do not know what you would consider a long time but I put one in soaking wet for a couple of minutes at full blast (by that time the water is more than boiling) and another couple minutes at half blast and that should get rid of pretty much anything. It certainly takes away any bad smell. Just make sure there is plenty of water on it at all times.
Another trick I have used for sponges, kitchen cloths, tovels, etc. is to put them in the pressure cooker for a while. Now that’s disinfecting!
I learned somewhere to rinse sponges thoroughly in cold water and squeeze them pretty dry to prevent bacteria from growing. I don’t know about the bacteria, but they don’t stink like they used to. In fact, they don’t stink at all.
Maybe I’ll search for a cite on this. Doesn’t seem to make sense, now that I think about it.
How do you spell Heloise? 
Peace,
mangeorge
Dr. Dean was recently asked a question about nuking underwear to kill yeast (by a woman who had yeast infection problems). He said the microwave would probably kill the yeast, but that if you put dry things like underwear (and, presumably for this case, a dry sponge) in a microwave, it may very well start on fire. So be careful if you decide to try this.
Sailor: I wash my tovels in the svink ven I’m in Sveden and Norvay. How about you?
Seriously, how about the ionizing effects of microwaves? I’d think any penetrating radiation of that intensity would do a number on proteins, genetic material, etc. Is the rate of ionization caused by microwaves significant for our purposes? I’d test it myself, but looking for cancer in flies is kind of messy after they explode. 
That’s kind of what I was afraid of.
I don’t like bleach, because I have scaly hands from a chronic condition (I work in a gas station, and gasoline makes your skin crack)
Of course I have no scientific backing on this, but it was my understanding that bacteria can’t survive very long on a dry surface or object. It needs moisture to survive at all. I’ve heard it recommended that you let your sponges completely dry out because of that. So for that reason I always have 2 sponges going at once. I use one, one day. Then the next day I use a different one while the first one dries out. Then I switch back. And my sponges never, ever smell bad.
I was just paging through the most recent Consumer Reports (July) and there is an article about antibacterials and disinfectants that discusses what to do about sponges, dishcloths, and towels:
“Disinfect used sponges and dishcloths frequently–at least every few days, ideally every day–by tucking them amid the smaller items on the top rack of your dishwasher, or rinsing them thoroughly and then soaking them in a disinfecting product. Microwaving them for a minute will also work, so long as they’re damp when they go into the oven. Dishcloths and dish towels can also be adequately disinfected by machine washing and drying, preferably with a little added bleach. Keeping them open to dry out helps, too.”
I should note that I think when they talk about going through the dishwasher, they include the heated dry cycle (they discussed that elsewhere in the article).