What's the most unsanitary item in your house? The toilet? Nope, think again. It's your trusty, well-used kitchen sponge. Sponges are germ vectors. Think about it; all those holes, the dampness, the bits of food ... perfect real estate for microorganisms to move into and throw a party. You could bleach the sponges, but we generally feel that less bleach in the environment is a better thing.
What kinds of microorganisms can be found in sponges? Well, the five major causes of food-borne illness such as salmonella, E.coli, campylobacter, clostridium perfringens, and staphylococcus are commonly found on sponges. And we wash our dishes and wipe down our counters with these? Ew!
So, what to do? Easy: zap them in the microwave! The heat generated by microwaving a sponge for two minutes kills 99% of the microbes. Please microwave sponges when they are wet, and never microwave them dry; they become fire hazards.