2007 GSA Denver Annual Meeting (28–31 October 2007)
Paper No. 109-8
Presentation Time: 3:45 PM-4:00 PM


WILLIAMS, Lynda B., School of Earth and Space Exploration, Arizona State University, Box 871404, Tempe, AZ 85287-1404, lynda.williams@asu.edu, HAYDEL, Shelley E., School of Life Sciences & Biodesign Inst, Arizona State University, Box 875401, Tempe, AZ 85287-5401, EBERL, Dennis D., U.S. Geological Survey, 3215 Marine St, Boulder, CO 80303-1066, and BLUM, Alex E., U.S. Geol Survey, M.S. 964 Box 25046 Denver Federal Center, Denver, CO 80225-0046

Natural clay minerals have been used to heal skin infections since the earliest recorded history. French green clays have recently been shown to heal Buruli ulcer, a ‘flesh-eating' infection by Mycobacterium ulcerans. These clays may reveal an antibacterial mechanism that could provide an inexpensive treatment for this and other skin infections.

In attempt to scientifically substantiate the observed effect of the French green clays on bacteria, we have examined the mineralogy and chemical composition of two different French green clays used in the treatment of Buruli ulcer. Tests of the affect of the two clays on a broad-spectrum of bacterial pathogens showed that one clay (CsAr02) promotes bacterial growth while another (CsAg02) kills bacteria.

Analyses of mineralogy (by X-ray diffraction), major element chemistry (by electron microprobe), trace element chemistry (by ICP-MS), and textural relationships (by high resolution SEM) were used to deduce that the killing mechanism is not physical (attraction between clay and bacteria), but by a chemical transfer. Mineralogically the two clays are similar, however their trace element chemistry differs. Cation exchange procedures remove the antibacterial component of the clay, and leachates are shown to effectively kill bacteria. Heating the clay to 900˚C destroys its structure and the oxidized product is no longer antibacterial. The pH of the clay and associated water is high (9.4-10), and may play an important role in the speciation of toxins.

We conclude that the chemistry of the water used to hydrate the clay poultices contains the critical antibacterial agent(s), and this chemistry is controlled by the clay mineral composition and surface properties. The clay that promotes bacterial growth (CsAr02) may have provoked the natural immune system of the patients infected with M. ulcerans. Treatment with the antibacterial clay (CsAg02) may then have sterilized the wound, promoting natural healing.

2007 GSA Denver Annual Meeting (28–31 October 2007)
General Information for this Meeting
Session No. 109
Positive and Beneficial Aspects of Earth Sciences in Public Health
Colorado Convention Center: 501
1:30 PM-5:30 PM, Monday, 29 October 2007

Geological Society of America Abstracts with Programs, Vol. 39, No. 6, p. 296

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