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Clays hold promise in fight against infections

April 07, 2008

Mud may be coming to a medicine cabinet or pharmacy near you.

Scientists from Arizona State University report that minerals from clay could provide inexpensive, highly-effective antimicrobials to fight methicillin-resistant Staphylococcus aureus (MRSA) infections that are moving out of health care settings and into the community. These “superbugs” are increasingly resistant to multiple antibiotics and cause thousands of deaths each year.

Unlike conventional antibiotics routinely administered by injection or pills, the so-called “healing clays” could be applied as rub-on creams or ointments to keep MRSA infections from spreading, according to researchers in ASU’s College of Liberal Arts and Sciences. The clays also show promise against a wide range of other harmful bacteria, including those that cause skin infections and food poisoning, they add. Their study, one of the first to explore the antimicrobial activity of natural clays in detail, was presented at the 235th national meeting of the American Chemical Society, the world’s largest scientific society.

Clays have been used for thousands of years as a remedy for infected wounds, indigestion, and other health problems, either by applying clay to the skin or eating it. Cleopatra’s famed beauty has been credited to her use of clay facials. Today, clays are still commonly used at health spas in the form of facials and mud baths. However, armed with new investigative tools, researchers Shelley Haydel and Lynda Williams are putting the clays to the test, scientifically.

“Clays are little chemical drug-stores in a packet,” says study co-leader Williams, a geochemist in the School of Earth and Space Exploration. “They contain literally hundreds of elements. Some of these compounds are beneficial but others aren’t. Our goal is to find out what nature is doing and see if we can find a better way to kill harmful bacteria.”

In their latest study, funded by the National Institutes of Health, Williams, Haydel and their colleagues collected more than 20 different clay samples from around the world to investigate their antibacterial activities. Study co-leader Haydel, a microbiologist in ASU’s School of Life Sciences and a researcher in ASU’s Biodesign Institute, tested each of the clays against bacteria known to cause human diseases. These bacteria include MRSA, Mycobacterium ulcerans (a microbe related to the tuberculosis bacterium that causes a flesh-eating disease known as Buruli ulcer), as well as E. coli and Salmonella (which cause food poisoning). The researchers identified at least two clays from the United States that kill or significantly reduce the growth of these bacteria, in addition to the one French green clay that launched their research in 2005. The antibacterial effect of the French clay was documented this year in the Journal of Antimicrobial Chemotherapy, with co-author Christine Remenih.

Identifying what specific compounds make these clays effective antibacterial agents presents a challenge, researchers say, but they credit their combined perspectives, coming as they do from two very different scientific disciplines, for their successes. Haydel and Williams note too that tools like electron and ion microscopy might also reveal how these antibacterial clays may interact with the cell membranes or cellular physiology of the bacteria to kill.

Williams and Haydel continue to test new clay samples from around the world to determine their germ-fighting potential. They hope that the more promising clays will be developed into a skin ointment or pill to fight a variety of bacterial infections or possibly as an agricultural wash to prevent food poisoning. Several companies have expressed interest in forming partnerships to develop the clays as antimicrobial agents, the scientists say.

But ordinary mud can contain dangerous bacteria as well as toxic minerals like arsenic and mercury, the researchers point out. Until healing clays are developed that are scientifically proven, which could take several years, they say that hand washing and other proper hygiene techniques may be the best bet for keeping MRSA and other harmful bacteria at bay.

To hear Williams and Haydel discuss their research, go to ASU School of Life Sciences podcast (#2), Science Studio: