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Name: mike
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Do the microwaves in a microwave kill bacteria or is it the heat that kills the bacteria? I am wondering this because i have a science fair project and i am searching for a project dealing with bacteria.

As far as I'm aware it is the heat that kill bacteria in a microwave, and they need quite some time to be dead. The spores that some kind of bacteria make to survive harsh conditions do not contain much water and they might survive microwaves. I'm not sure what bacteria do that can survive high dosis of radiation, like Deinococcus radiodurans. They can do this by a very efficient repair system for their DNA. My guess is that they would also be killed by the heat generated in a microwave but I haven't found any data on this.

One word of warning: bacteria that spill food may be killed in a microwave, but the toxins that they produce are the actual substances that make us ill, and they are not destroyed by microwaves. So food that has gone off is not safe to eat after microwaving.

For your science project on bacteria, have a look at the Virtual Museum of Bacteria at

Dr. Wassenaar

It's the heat. Microwaves specifically excite molecular rotations; these do not have any direct effect on the integrity of living systems. However, the energy in these rotational modes of motion eventually becomes general heat released to the surroundings; if enough microwave energy is dumped into a system, it will get hot. Increased temperature does cause irreversible chemical changes in living systems, abd that is what kills them.

Richard E. Barrans Jr.

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