The scientific approach to studies of antibacterial clay relies on observation, hypothesis formulation and hypothesis testing. The work that led to identifying the mechanism of certain antibacterial clays started with the careful observations of Line Brunet de Courssou, a French philanthropist who photographically documented the healing of Buruli ulcer, a mycobacterial skin infection (click here for info - Warning: graphic images). Therefore, any information or photo-documentation on the use of clays in healing topical infevtctions would be appreciated.

Feel free to request a  sample and send input to antibacterialclays@gmail.com.

Samples come in one-ounce tubs and might last months to years, depending on frequency of use. We suggest adding a little water to the container, smushing it around, and then applying a thin layer of the paste.

In 2002, Line Brunet de Courssou, a philanthropist working in Cote d’Ivoire, Africa, observed that French Green clays killed Buruli ulcer. This infection, by Mycobacterium ulcerans, is a flesh-eating disease that attacks the subcutaneous lipids causing flesh removal over large areas of the body. Courssou had presented to the World Health Organization (WHO), photo-documentation of her treatment of over a hundred people with the disease. Using daily applications of the green clay poultice (mud), she healed infections that did not respond to any known antibiotic, and normally required excision or amputation for advanced cases.

Our decade of research on clays that kill human pathogens, including antibiotic resistant strains such as methicillin resistant S. aureus (MRSA), has since documented their common characteristics. Having tested dozens of clays worldwide, similar to the French green clay, about 10% have shown antibacterial effects on model Gram positive and Gram negative pathogens. Common among the antibacterial clays are that they each contain phases with reduced iron (e.g., pyrite, magnetite, jarosite) and phyllosilicates including dominantly illite-smectite. However, the mineralogy alone does not define antibacterial clay. Another common characteristic is the dominance of nanometric particle sizes. Testing various size fractions of clay has shown that the finest fraction (<0.1µm) is antibacterial, whereas the coarser fractions are not. Furthermore, oxidation of the clay removes the antibacterial effect.

Critically important is the role of the clay mineral surface in buffering the water pH to conditions <4 or >10, where Al and Fe dissolve from various minerals in the clay. Because of the enormous surface area of expandable clays (smectites), metals adsorb to their interlayer surfaces. When the clays are taken out of their natural environment and mixed with de-ionized water for a medicinal poultice, cation exchange and mineral dissolution releases reduced metals that become oxidized, generating hydroxyl radicals that damage organic compounds in the bacterial cell and cause metabolic malfunction in the bacteria. Different modes of action have been documented for different clay mineralogies, but in each case the role of the clay is either to flood pathogens with toxic metals (e.g., Fe, Al), or to rob bacteria of essential nutrients (Ca, Mg, P). Lessons learned will drive the design of new treatments for antibiotic resistant bacteria.

 The discovery and development of novel antibacterial agents is essential to address the rising health concern over antibiotic resistant bacteria. This research investigated the antibacterial activity of a natural clay deposit near Crater Lake, Oregon, that is effective at killing antibiotic resistant human pathogens. The primary rock types in the deposit are andesitic pyroclastic materials, which have been hydrothermally altered into argillic clay zones. High-sulfidation (acidic) alteration produced clay zones with elevated pyrite (18%), illite-smectite (I-S) (70% illite), elemental sulfur, kaolinite and carbonates. Low-sulfidation alteration at neutral pH generated clay zones with lower pyrite concentrations (4-6%), the mixed-layered I-S clay rectorite (R1, I-S) and quartz.

Antibacterial susceptibility testing reveals that hydrated clays containing pyrite and I-S are effective at killing (100%) of the model pathogens tested (e.g., E. coli and S. epidermidis) when pH (< 4.2) and Eh (> 450 mV) promote pyrite oxidation and mineral dissolution, releasing > 1 mM concentrations of Fe2+, Fe3+ and Al3+. However, certain oxidized clay zones containing no pyrite still inhibited bacterial growth. These clays buffered solutions to low pH (< 4.7) and oxidizing Eh (> 400 mV) conditions, releasing lower amounts (< 1 mM) of Fe and Al. The presence of carbonate in the clays eliminated antibacterial activity due to increases in pH, which lower pyrite oxidation and mineral dissolution rates.

The antibacterial mechanism of these natural clays was explored using metal toxicity and genetic assays, along with advanced bioimaging techniques. Antibacterial clays provide a continuous reservoir of Fe2+, Fe3+ and Al3+ that synergistically attack pathogens while generating hydrogen peroxide (H2O2). Results show that dissolved Fe2+ and Al3+ are adsorbed to bacterial envelopes, causing protein misfolding and oxidation in the outer membrane. Only Fe2+ is taken up by the interior of the cells, generating oxidative stress that damages DNA and proteins. Excess Fe2+ oxidizes inside the cell and precipitates Fe3+ oxides, marking the sites of hydroxyl radical (•OH) generation. Recognition of this novel geochemical antibacterial process should inform designs of new mineral-based antibacterial agents and could provide a new economic industry for such clays.