Killer Clays! Natural antibacterial clay minerals

Clay minerals have been used in medicinal applications since Aboriginal times (Carretaro, 2002; Wilson, 2003). Clay poultices are used to heal wounds; people eat clays to coat stomach linings and soothe indigestion; animals eat clay containing trace elements (e.g., As) that can kill worms. The reasons that various clay minerals are effective as medicines may be as variable as the ailment, but by studying the mechanisms by which clay minerals heal, we may gain insight to a variety of diseases and potential cures. The Romans first recorded studies on medicinal uses of clay minerals in 60 BC (Carretero, 2002) and Aristotle first mentioned the practice of eating clays (Mahaney et al., 2000). Most early research focused on the physical properties of clay minerals, which benefit digestion or protect and cleanse the skin. Smectite clay minerals can adsorb dissolved and suspended substances such as toxins, bacteria and viruses, while kaolinite and palygorskite are primarily used to soothe the digestive tract (Carretero, 2002). The physical adsorption of water and organic matter is the most common attribute of the healing properties of clays, however the chemical interaction of clay minerals with bacteria has received less attention. We have only begun to investigate the clay chemical properties that may be important in medicine, but our results indicate that particular natural clay minerals can have striking and very specific effects on microbial populations. The effects can range from enhanced microbial growth to