Working in tandem, chemically reduced iron (Fe2+) and aluminum (Al3+) in blue clays can kill pathogenic bacteria, such as these E. coli cells. Credit: ASU
“We think of this mechanism like the Trojan horse attack in ancient Greece,” said Lynda Williams, a clay-mineral scientist at ASU’s School of Earth and Space Exploration (SESE). “Two elements in the clay work in tandem to kill bacteria.”
She explained, “One metallic element – chemically reduced iron, which in small amounts is required by a bacterial cell for nutrition – tricks the cell into opening its wall. Then another element – aluminum – props the cell wall open, allowing a flood of iron to enter the cell. This overabundance of iron then poisons the cell, killing it as the reduced iron becomes oxidized.”
A chance discovery of a medicinal clay from Europe caught Williams’ attention and put her on the track. A French philanthropist with clinical experience in Africa told her about a particular green-hued clay found near the philanthropist’s childhood home in France. The philanthropist, Line Brunet de Courssou, had taken samples of the clay to Africa, where she documented its cure for Buruli ulcer, a flesh-eating skin disease, in Cote d’Ivoire (Ivory Coast).
Williams attempted to locate the site of the green clay deposit, which was in the French Massif Central region. When the search proved unsuccessful, she systematically tested clays sold online as “healing clays.” After testing dozens of samples, Williams and her team identified a blue-colored clay from the Oregon Cascades that proved to be highly antibacterial, against a broad spectrum of human pathogens, including antibiotic-resistant strains such as MRSA.
The colors of the clays reflect their origins, Williams said. The greens and blues of antibacterial clays come from having a high content of chemically reduced iron (Fe2+), as opposed to oxidized iron (Fe3+), which gives the familiar red color of rust (Fe-oxide), often associated with many clays. Reduced clays are common in many parts of the world, typically forming in volcanic ash layers as rocks become altered by water that is oxygen-deprived and hydrogen-rich.
Because blue and green clays are found abundantly in nature, Williams said, this discovery of how their antibacterial action works should lead to alternative ways of treating infections and diseases that are persistent and hard to heal with antibiotics. Williams said, “Discovery of how natural clays kill human pathogens may lead to a new economic use of such clays and also to new drug designs.” http://asunow.asu.edu/20160106-asu-scientists-discover-how-blue-and-green-clays-kill-bacteria
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