How blue and green clay kills bacteria.

Since prehistoric times, clay have been used by people for medicinal purposes. Whether by eating it, soaking in a mud bath, or using it to stop bleeding from wounds, clay has long been part of keeping humans healthy. Now scientists have discovered the two key ingredients that give some natural clays the power to kill even antibiotic-resistant microbes. A new discovery by Arizona State University scientists shows exactly how two specific metallic elements in the right kinds of clay can kill troublesome bacteria that infect humans and animals."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 patients in the African country of Cote d'Ivoire (Ivory Coast). The research include testing dozens of samples, Williams and her team identified a blue-colored clay from the Oregon Cascades that proved to be highly antibacterial. The research reported in the paper shows that it works against a broad spectrum of human pathogens, including antibiotic-resistant strains such as methicillin-resistant Staphylococcus aureus (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. source; science daily.