The antibiotic properties of certain clays have been explained, hopefully leading the way to the production of more reliable antibiotic-resistant treatments for wounds.
Clays have a long tradition of medicinal use, including to treat wounds. The success of such folk medicines is mixed, but scientific testing has shown that some clays do have powerful antibiotic properties. With so many different sorts of clay in the world, however, just going into your back garden and digging some up is not a wise way to prevent infection.
Professor Lynda Williams of Arizona State University is identifying which clays work, and shedding light on why.
Sixteen years ago Williams got a message from Line Brunet de Courssou, who described her success in treating residents of Ivory Coast suffering from Buruli ulcers using French green clay.
Courssou's marriage to a French diplomat had brought her to Africa, and while there she became disturbed at the frequency of the ulcers, caused by Mycobacterium ulcerans. Given the limited access to modern antibiotics in one of the poorest countries on Earth, Courssou turned to a family remedy. The clay worked, but Courssou didn't know why and emailed clay researchers around the world in the hope of getting an explanation.
After years of research, Williams concluded Courssou's success was part luck. When Williams tested two French green clays she found one was indeed a potent killer of M. ulcerans, but the other actually promoted the growth of the bacteria. If Courssou had used the wrong clay she could have made things significantly worse.
This inspired Williams to test a range of clays from around the world, reporting in 2013 that blue clays collected from Crater Lake, Oregon, were the most effective she could find. At the time she attributed the effectiveness to a combination of the clay making the wound environment too acidic for the bacteria, and iron oxidation.