Antibiotics in ancient bones: tetracycline and glowing human remains

South of ancient Egypt was a land called Nubia, and archaeologists have made a surprising finding there too: signs that the Nubians were being exposed to antibiotics! Human bones recovered from the area glow green under UV light which is due to tetracycline, an antibiotic we use today, embedded in the bone. The University of Cambridge’s Tamsin O’Connell is an archaeological scientist, and she spoke with Eva Higginbotham to explain the story...

Tamsin - They were getting it from things that they were eating or drinking, and we think it's an accidental product that gets in there. So if they're consuming something like beer or bread made from grain that might have tetracycline in it, then that gets incorporated into their bones. And a long time later, we get to see it glowing under UV light.

Eva - Why might there be tetracycline in grains?

Tamsin - Tetracycline is a naturally occurring product of fungi, and it occurs naturally when fungi grow under certain conditions. And that can be when grain is stored in slightly damp environments. So if they're having a wheat harvest and then putting it in a big grain storage area and you have water that's kind of coming up and going down in the ground, then that could make the green at the bottom go slightly mouldy. It would still be good enough to eat, but it might contain kind of trace levels of tetracycline.

Eva - I see so if they then use that wheat to make beer or bread, then they're going to be accidentally eating tetracycline. So then how does the tetracycline get from being eaten as bread to being incorporated into bone?

Tamsin - So tetracycline, it's quite a big molecule and it's got a ring structure in it of carbon chains, and its structure loves to bond to calcium, and there's a lot of calcium in your bones. And so as bones are growing, as this calcium phosphate, which is in your bones, is being laid down, if there's something in your bloodstream that likes to bond to it, then it will just be kind of stuck in there and it will hang around forever.

Eva - So does that mean that if you've ever taken tetracycline, then you have some glowing bones?

Tamsin - Yes, pretty well. So the bits of your bones that were being remade, remodelled, turned over, when you were taking tetracycline or any similar sort of antibiotic, that includes things like doxycycline which is an anti-malarial, those bits of your bones will glow if you could get them out and look at them under UV light.

Eva - So maybe try to avoid that for now then! How do we know though that the tetracycline got into the bone because it was incorporated by the bone owner throughout their lifetime, rather than it got into the bone through some sort of contamination? Because it has been thousands of years.

Tamsin - That is a really good question. And whenever we find anything in archaeological samples, we have to question whether or not it's naturally occurring, if it came in during the individual's lifetime, or if it came in later on. And the shape of the glowing lines within the bones tells us that it looks like it's sort of on the growing face of a bone cell being formed rather than percolating in from contamination later on.

Eva - I see. So it's sort of just in the right place to mean, all right, this got in there because it was being incorporated officially as part of bone rather than randomly slapped on afterwards?

Tamsin - Yes. It's worth saying that tetracycline is used as a label in modern day studies of bone turnover and bone remodelling, so we know an awful lot about what it should look like when it's being taken up by living and growing bone. And so comparing the archaeological bones and the patterning, what we see there, with what we know we see in modern bones when tetracycline is being used as a bone label, gives us confidence that it is being laid down when these people were alive.

Eva - And do you think that it could have had some sort of health benefits? Is there enough tetracycline in there that it could have had a benefit to the person consuming it?

Tamsin - Having low grade antibiotics in your diet could have some benefit if people were having bacterial infections. But we really can't say that they knew that it was of health benefit to them. Although we do know from the texts that beer dregs are often included as an ingredient in medical prescriptions from a roundabout this time - 4,000 years ago. And so it's possible that they knew that there were some good things that they were accidentally getting in beer and bread.

Eva - So do we have any other evidence of ancient Egyptians or other civilisations taking antibiotics possibly on purpose?

Tamsin - Not that they're taking it on purpose, but we can see tetracycline in bones from other populations. So it's been found in people who were living in Herculaneum at the time of the eruption of Vesuvius. I would speculate that any population where grain has been stored and could have got mouldy, we'd be able to see some tetracycline in there