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

MRSAStaphylococcus

Buruli

First, let’s define what are clays?

Common misconceptions between

CLAY SIZE & CLAY MINERALOGY

Clays are a fine grained particlesize less than 2 µm diameter

The mineralogy of claydeposits 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 agentssince antiquity

- Studies indicate that different metals cause discrete and distinct types of cell damage

http://www.nature.com/nrmicro/journal/v11/n6/full/nrmicro3028.html

Experimental Methods

In Vitro Antibacterial Testing

- Bacterial Plate Counting

- Disk Diffusion

Testing clays for their antibacterial properties

Rhodes Clays, North CarolinaOMT Clays, Oregon

Greeney’s Clays, New YorkWalker’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: 0.2121

Mineral Weight %

NON-CLAYS  

Quartz 59.0Kspar (ordered Microcline)

3.0

Plagioclase (albite, var. cleavelandite)

8.5

Calcite (Mg-rich) 0.2

Halite 0.0

Gypsum 0.0

   

Total non-clays 70.8

   

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 clays 19.9

TOTAL 90.7

XRD Mineral Analysis

Fit With Quartz Walker

Full pattern degree of fit: 0.1974

Mineral Weight %

NON-CLAYS  Quartz 10.7Plagioclase (albite, var.) 5.0Plagioclase (oligoclase) 8.8Gypsum 3.7Jarosite (Mex) 9.1   Total non-clays 37.3   

CLAYS  Kaolinite (disordered) 6.0Smectite (Na-Kinney) 53.3Chlorite (CMM) 3.4Chlorite (Mg; Luzenac) 0.0   Total clays 62.7   

TOTAL 100.0

- 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!