Frogs Could Provide Big Leap in Antibiotics

A bit of old Russian folk wisdom could produce a crop of new antibiotics.

With drug-resistant bacteria a growing public health threat worldwide, a type of frog Russians have used to keep milk fresh could provide a fresh source of germ fighters.

Moscow State University chemist Albert Lebedev grew up in a rural part of Russia, where many people kept their own cows. In the days before refrigeration, it was a challenge to keep milk from spoiling.

So people enlisted the help of the local amphibians.

“[For] small portions of milk to drink, they used to put [a] frog inside," he says. "A small frog over there could prevent the milk from being spoiled.”

It turns out that putting a frog in your milk is not as crazy as it might sound.

Frog surgery

To explain, let’s go back about 25 years, to another surprising discovery about amphibians.

The eggs of African horned frogs are a popular tool for scientists studying the innermost workings of cells. In the late 1980s, Michael Zasloff was surgically removing frog ovaries for his research at the National Institutes of Health.

Zasloff noticed that when he put the frogs back in their slimy aquarium homes, without the benefit of antibiotics, “The frogs healed after surgery without exhibiting any signs of infection or inflammation.”

Zasloff and his colleagues discovered that’s because the skin of the African horned frog produces unique anti-microbial compounds.

Potent cocktails

Then they discovered that other species of frog also produce potent cocktails of antibiotics.

“What is amazing is that no two frogs have the same cocktail," he says. "They’re all different, and all beautifully tuned to deal with the microbes that these animals face.”

And for frogs, dealing with microbes on their skin is a matter of life and death. They breathe and drink through their skin, and spend much of their time in waters teeming with microbes.

Moscow State University’s Albert Lebedev says the more scientists looked, the more kinds of chemicals they found coming out of the skins of amphibians.

“They can be antifungal, antiviral, antibacterial, antitumor, neuropeptides, analgesics," and so on," he says. "So, a lot of various functions.”

Milk preservatives

All of these functions are performed by chemicals known as peptides.

When Lebedev studied the frogs Russians used to keep their milk fresh, “We found something like 80 peptides," he says.

And each one is apparently responsible for something.

"We don’t know now exactly what every peptide is for,” he says, "but they do know that several of them kill Staph bacteria, a kind of germ responsible for serious skin infections; and Salmonella, which causes food poisoning.

That would explain why a frog in the milk keeps it fresh.

Lebedev says the frog chemicals work at very, very low concentrations, “which is fantastic. This is the scale of activity of very potent antibiotics.”

It will be years before these antibiotics find their way into doctor’s offices and hospitals, if they ever do. Lebedev says developing peptide drugs is expensive and difficult.

But some are in development. Michael Zasloff, now at Georgetown University, has been working on a drug to treat diabetic foot infections, based on one of the African horned frog peptides.