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Death by a thousand cuts: how antibacterial clays kill JANUARY 25, 2016 ~ BETTY

Posted by Shawna Rothery on


By now most of you will have heard that more and more bacteria are becoming impervious to the many life-saving antibiotics on which we’ve come to rely. In November, scientists in China sampling bacteria from meat and hospitalized patients found a new gene called MCR-1 that confers resistance to colistin, a drug that is currently used as a last resort when all other antibiotics have failed. This report was the latest in a series of increasingly worrisome news that have spurred researchers to look for new ways to combat antimicrobial resistance. While some scientists are exploring futuristic ideas like light-activated nanoparticles, others are looking to nature and literally digging up dirt for inspiration.

In a paper published recently in Scientific Reports, researchers have revealed for the first time the mechanism behind the antibacterial properties of medicinal clay.

“People have been eating clays for thousands of years,” says Dr. Keith Morrison, the report’s lead author and now a postdoctoral fellow at the Lawrence Livermore National Laboratory. The purported benefits of eating clay relate to its ability to grab heavy metals and other “toxins” and expel them from your body. However, the scientific evidence supporting this idea (and the idea that our bodies need any detoxing at all) is lacking.

As a PhD student at Arizona State University, Morrison was interested in another curious property of some medicinal clays—their ability to kill bacteria. While the use of clay to treat wounds and skin infections can be traced back to the 19th century, the scientific study of these antibacterial clays is a fairly new field.

Dr. Lynda Williams was Morrison’s PhD supervisor and one of the first people to apply the rigours of scientific testing to antibacterial clays. In a 2008 paper,Williams and her team tested the antibacterial activities of two types of French green clay against a diverse group of bacterial pathogens. Despite the fact that both clay minerals had been used to treat Buruli ulcers, a flesh eating disease caused by the bacteria Mycobacterium ulcerans, only one type of clay was able to kill bacteria in the lab. “Lynda’s lab was the only lab out there doing anything like this,” says Morrison. “I saw it and immediately knew that’s what I wanted to work on.”

Their study of the French green clays prompted them to look for other deposits of antibacterial clays. In the clay deposits near Crater Lake in the Cascade Mountains of Oregon, they struck pay dirt. In a 2014 paper, Morrison and Williams showed that the blue clays in the deposit, which is an estimated 20 to 30 million years old, effectively killed cultures of Escherichia coli andStaphylococcus epidermidis. Further testing showed that the clays were also 100% effective in killing other human pathogens including antibiotic resistant bacteria like methicillin resistant Staphylococcus aureus (MRSA).

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