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As we fire up our summertime grills, I wonder: Why do different foods have to be cooked to different temperatures to be safe? Does a bacterium have different heat thresholds in beef versus chicken? —Mary Mallon
Congrats, Mary, on one of the subtler pseudonyms to come across this desk. Come, let us smugly watch as the others Google it.
As most of us are now aware, everything in the world, including our own bodies, is lousy with bacteria. It was once believed the average person's body contained 10 times as many free-riding bacterial cells as actual human cells.
Recent estimates are more conservative, and it's now generally held that the number of bacterial cells you're carrying and the number of human cells you're made of are roughly the same.
The vast majority of these bacterial cells hang out in the contents of your gastrointestinal tract, which has led one wag to observe that the question of whether you're outnumbered by your bacteria depends mostly on how recently you've had a bowel movement. So remember: If you're ever planning to have some kind of election in your body, make sure to take a big poop first.
I say all this, not merely to fill space, but also to stress the fact that bacteria are inescapable. And if you think you're full of them, you should see the animals we raise for food.
That said, different animals present different hazards. Poultry is well-known for carrying salmonella, as well as an equally unpleasant pathogen called Campylobacter. Both of these bacteria are found throughout the host's tissues, meaning you need to bring every part of your bird to 165 degrees to make sure you're not eating any live ones.
With cattle, the main worry is E. coli. This bacterium confines itself to the cow's gut—it isn't found in muscle tissue, which is why a rare steak with a cool red center won't kill you.
That said, slaughterhouses are messy places, and once they start cutting an animal up, its gut flora get everywhere, which is why ground beef, like chicken, also needs to be cooked to a temperature of 165 degrees—it probably has at least a little cowshit in it. Happy Fourth of July!