Do microwave ovens kill bacteria?

[jeffl]

http://www.straightdope.com/columns/...-kill-bacteria

The question here:
"If I take a piece of pizza that's been sitting on the table awhile and microwave it for one minute, would that kill bacteria and decrease the chance of food poisoning, or am I just eating nice hot bacteria?"

I found the answer to this question to be completely ineffective. The science was there, but the correct answer is not. Microwaving long enough may kill bacteria, but it is not bacteria that causes food poisoning, it is the toxins created by the bacteria. You can microwave toxins all you want, but it won't get rid of them. Thus, while your microwave may kill off the bacteria, it will not achieve the desired result of preventing food poisoning.

[Bozuit]

I'm not a doctor or anything even vaguely medical, but I'm pretty sure you're wrong and food poisoning can be caused by eating toxins or eating live bacteria (or viruses, parasites etc.) which then make you sick in their own way.

Also, the specific question does seem to imply that the pizza is not old enough to have a lot of toxins in it. It was never specified that it wasn't old, but I think it's reasonable to assume the food is not at that point if it's not explicitly mentioned either way.

Finally, the question asked if it will "reduce" chances of food poisoning. The chances of that will surely always be reduced by killing bacteria that can cause it, unless the chance is already at 100%.

[jeffl]

If it wasn't obvious, I meant that it's not just bacteria, but also toxins that can cause illness.

The question asks about pizza that has been sitting out for a while--not four hours, not 10 hours, but an ambiguous "while."

Just because something isn't explicitly mentioned, doesn't mean it should be disregarded. As any question asked, the assumptions you make should revolve around the inquirer's concern. In this case, he was concerned about food poisoning from pizza that could have been left out. If you're going to assume that the pizza wasn't left out long enough to produce toxins, there's no reason you should assume that any of the various bacterias are harmful without toxins. Often, it is the case that they are completely harmless without toxins. So why are you even microwaving it then?

I'm pretty sure he would have liked to know about the toxins, and I'm pretty sure that Cecil left them out because he didn't know about them. If the inquirer simply wanted to reduce the chances of food poisoning, the more appropriate answer would have been to slam the slice of pizza on a clean plate upside down. That would save you both time and energy!

[Crazyhorse]

Originally Posted by jeffl

The question asks about pizza that has been sitting out for a while--not four hours, not 10 hours, but an ambiguous "while."

The question was:

If I take a piece of pizza that's been sitting on the table awhile and microwave it for one minute, would that kill bacteria and decrease the chance of food poisoning, or am I just eating nice hot bacteria?

The answer was yes, the heat from microwaving it sufficiently would kill at least some bacteria and therefore at least somewhat decrease the chance of food poisoning.

I don't disagree that food poisoning by toxins could have been added as pertinent supplemental information. It is an important thing to consider in the general question of food poisoning and cooking, but the question was answered accurately in the frame of how it was asked. But the vast majority of food poisoning is caused by live bacterial infection or viruses. According to this guide there are only three species of bacteria that create toxins sufficient for causing illness without live bacteria.

Only three bacterial species are considered important causes of the intoxication type of food poisoning. These are Bacillus cereus, Clostridium botulinum and Staphylococcus aureus, all of which are capable of causing illness by producing toxins in food. There are several other species of Bacillus and Clostridium that have been reported to produce pre-formed toxins in food, such as B. licheniformis and Cl. butyricum, but these are uncommon and not considered further here.

Out of those three, about half of the toxins they might produce are not heat-stable and the toxin would be neutralized by cooking heat. But you are correct that out of those few toxins remaining that are heat-stable (among the thousands of other ways one might get food poisoning) their mere presence on the pizza pie in question would make the questioner sick even after being heated.

[Bozuit]

Originally Posted by jeffl

If it wasn't obvious, I meant that it's not just bacteria, but also toxins that can cause illness.

Well, no it wasn't obvious because you clearly said it's "not bacteria" that cause it.

I think the most you can argue with about Cecil's reply is that he didn't mention that killing bacteria will not remove toxins if they're already present. But since the question was essentially "will microwaving a piece of pizza for one minute kill the bacteria in it?" I think it was a reasonable answer.

[Fear Itself]

Some bacteria produce toxins that are destroyed by heat. Clostridium botulinum toxin is destroyed if boiled for ten minutes.

[janeslogin]

I got a degree in medical microbiology many decades ago.

A question I have long mused is will microwaving kill spores of the gram positive rods that may cause food poisoning. I could look it up I suppose. I've just never bothered to research it as I have never used microwaving as a tool to produce safe food.

BTW, in the laboratory back there and back then we always had a time and temperature specification for sterilizing. Safe food probably, perhaps usually, means something less than sterile.

[janeslogin]

[One time bump to see if the weekday participants have any opinion on my musings above.] " ... will microwaving kill spores of the gram positive rods that may cause food poisoning." ?

[Ethilrist]

My assumption would be that even if it is possible for microwaving to kill bad stuff, the microwaves I have used had dead spots in them that wouldn't heat the food evenly.

So, use a toaster oven.

[TriPolar]

Heat, the by product of microwaves, will kill some bacteria and break down some toxins. So in some narrow range of conditions, microwaving a slice of pizza will decrease the chance of food poisoning. In a much broader range of conditions microwaving won't help. But probably the conditions for a slice of pizza sitting on a table for a while are already within the safe range to start with.

That also assumes that pizza is not a magic food which never goes bad.