Natural Antibacterial Clay Mineralogy ~ Medical Geology ~ Clélia Tommi & Dr. Lynda Williams School of Earth & Space Exploration

Why do Antibacterial Clay Research? - Overuse of antibiotics around the world - Proliferation of antimicrobial resistance strains - Identification of new antibacterial agents - What makes a natural clay antibacterial? 1 MRSA Staphylococcus Buruli

First, let’s define what are clays? Common misconceptions between CLAY SIZE & CLAY MINERALOGY Clays are a fine grained particle size less than 2 µm diameter The mineralogy of clay deposits is variable but mostly composed of phyllosilicate minerals.

What makes the structure of clays so important? - Interlayer cations can exchange when hydrated TETRAHEDRAL OCTAHEDRAL TETRAHEDRAL Interlayer CATIONS TETRAHEDRAL OCTAHEDRAL TETRAHEDRAL

What makes the structure of clays so important?

Electron Microscopy of Clay Minerals

How does clay interact with the bacteria? - Metals have been used as antimicrobial agents since antiquity - Studies indicate that different metals cause discrete and distinct types of cell damage

Experimental Methods In Vitro Antibacterial Testing - Bacterial Plate Counting - Disk Diffusion Testing clays for their antibacterial properties Rhodes Clays, North Carolina OMT Clays, Oregon Greeney’s Clays, New York Walker’s Clays, Nevada Mineral Analysis -X-Ray Diffraction -RockJock Analysis

In Vitro Antibacterial Susceptibility Testing - Bacterial Plate Counts Summary of bar graph showing E.coli growth in sample incubated with clay minerals

- Disk Diffusion In Vitro Antibacterial Susceptibility Testing Petri dishes showing the zone of inhibition for the OMT clay (24 mm), compared to the Rhodes clay that is not antibacterial Petri dishes showing zone of inhibition - 0 mm Rhodes - 0 mm Greeney - 24 mm OMT - 50 mm Walker

XRD Mineral Analysis -Random powder X-Ray Diffraction pattern of the Greeney Clays Sample name:Greeney Full pattern degree of fit: MineralWeight % NON-CLAYS Quartz59.0 Kspar (ordered Microcline) 3.0 Plagioclase (albite, var. cleavelandite) 8.5 Calcite (Mg-rich)0.2 Halite0.0 Gypsum0.0 Total non-clays70.8 CLAYS Smectite (Na-Kinney)3.9 Illite (1Md)4.3 Chlorite (Mg; Luzenac)2.2 Muscovite (2M1)5.2 Illite (R0; 5%I)4.3 Total clays19.9 TOTAL90.7

XRD Mineral Analysis Fit With QuartzWalker Full pattern degree of fit: MineralWeight % NON-CLAYS Quartz10.7 Plagioclase (albite, var.)5.0 Plagioclase (oligoclase)8.8 Gypsum3.7 Jarosite (Mex)9.1 Total non-clays37.3 CLAYS Kaolinite (disordered)6.0 Smectite (Na-Kinney)53.3 Chlorite (CMM)3.4 Chlorite (Mg; Luzenac)0.0 Total clays62.7 TOTAL Random powder X-Ray Diffraction pattern of the Walker Clay

Conclusions - Antibacterial testing showed that the Rhodes and the Greeney clay are not antibacterial, but the OMT and Walker clay are. - XRD shows the presence of goethite and anhydrite in the Rhodes and Greeney clay, suggesting oxidation. Other minerals are igneous and metamorphic assemblages. - The antibacterial clays (OMT and Walker) are hydrothermally altered deposits that contain reduced metals (e.g., pyrite). - The oxidation state (Eh) and acidity (pH) of the clays equilibrated with water is important to the antibacterial effect.

Questions? - Disk Diffusion Thank you!