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If eggs could talk, they might say it's not their fault. Eggs get contaminated because the hen that is laying them is infected. Eggs themselves, if they come from a healthy bird, are remarkably resistant to contamination, as Anna Vigran reports.

ANNA VIGRAN: John Ingraham's backyard is pretty typical for suburban Sacramento, except for the large chicken coop tucked in-between the clothesline and the gleaming pool. Its 13 residents strut proudly and keep John up to date with their news.

(Soundbite of chicken clucking)

Mr. JOHN INGRAHAM (Microbiologist): It means they've laid an egg and they're cackling. Isn't it curious that they would announce to the world that they've laid an egg rather than keep it a secret?

VIGRAN: John is my grandfather, and he's also a microbiologist. He spent years exploring the world of tiny organisms. And so-called retirement hasn't changed that.

He says there are very few places in the world that are naturally germ-free, but eggs from a healthy bird are one of them.�

Mr. INGRAHAM: The reason they stay germ free is because of their chemical defenses.

VIGRAN: Bacteria may get through a crack in the shell or the membrane underneath, but then the egg white fights back.

Mr. INGRAHAM: And inside there's three proteins that are very effective antibacterial agents.

VIGRAN: One is called lysozyme. It isn't just in egg whites - it's in tears, saliva and the drippy stuff that comes out of your nose.

Mr. INGRAHAM: And lysozyme has the honor of being discovered by Sir Alexander Fleming, who also discovered penicillin.

VIGRAN: Fleming happened to notice that when drips from his nose dropped onto certain bacteria, they died.

Mr. INGRAHAM: The lysozyme kills bacteria by breaking down their cell wall.

VIGRAN: Lysozyme doesn't work on everything, but it can pop a lot of bacteria. And the egg white has two other ways to kill invaders. There's a protein that prevents bacteria from getting an essential vitamin. And another, called conalbumin, that deprives microbes of iron, which they need to grow.

It's a pretty effective system, though John says there was an incident several years ago when a certain egg processor suddenly had all their eggs go bad.

Mr. INGRAHAM: No one could figure out why, and it turned out they were washing their eggs in iron pans.

VIGRAN: Which meant there was just more iron than the conalbumin could mop up, leaving plenty for the microbes.

Mr. INGRAHAM: Hi, ladies. Hi, ladies. Uh-huh. Yeah. We've got two, uh-huh - one for each of us if we want one for breakfast.

VIGRAN: John reaches into the nest box and pulls them out. I know these are probably the most spoiled chickens ever, but looking at their living quarters, I'm pretty glad to know their eggs have ways to keep microbes out. And John says the eggs will stay microbe-free for several weeks, even at room temperature.

But wait a minute. I thought we were told to keep eggs in the fridge and not to eat raw eggs or things with raw eggs in them, because of salmonella. John says if the eggs come from healthy chickens like his, there's no problem. But as the current recall shows...

Dr. INGRAHAM: Chickens tend to be notoriously susceptible to infection to salmonella.

VIGRAN: And if the chicken that's laying the egg is infected with salmonella, it's likely its eggs will be infected, too, which is why you're told to cook eggs, to be on the safe side, since most chickens don't get to live in the backyard.

(Soundbite of a knock)

Dr. INGRAHAM: So then, break an egg.

VIGRAN: But I'm about to get a surprise.

(Soundbite of a cracking of egg)

Dr. INGRAHAM: Even a broken egg will last quite a while if it's not cooked, but a cooked egg won't last very long, because you've inactivated the proteins.

VIGRAN: So, no hard-boiling eggs unless you're planning on eating them right away. And if you've got eggs from super healthy chickens like my grandfather's, why not eat them right away? They taste wonderful.

Dr. INGRAHAM: Mm. Mm-hmm. That is some good egg.

(Soundbite of laughter)

VIGRAN: For NPR News, this is Anna Vigran.

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