The Potential use of Clay as a Biological Weapon in the War Against Superbugs

Antibiotics discovered between the 1930s-1960s are some of the most significant, life saving discoveries in the history of medicine. However, we have failed to keep pace with the ability of many pathogens to develop resistance to antibiotics. Clinical isolates of many pathogenic bacterial species are now resistant to antibiotics. Although improved global surveillance and control practices can prevent acquisition and transmission of resistance, the desperate need for novel antibacterial agents cannot be overstated.

Previous research had shown that natural mineral clay (French Green Clay) may be promising in the battle against the antibiotic-resistant Buruli ulcer. We previously reported identification of antibacterial activity in several natural clays using an E.Coli growth inhibition assay. Of the six natural clays tested, Magnesium Bentonite Clay (MBC) exhibited the highest anti-bacterial activity.  Building on these findings, the current study focused on characterizing the antibacterial properties in MBC. The goal was to investigate the mechanism and the spectrum of MBC’s antibacterial activity.

To characterize MBC’s antibacterial properties, a experiment was designed to test if the property was associated with a soluble element. Clay was suspended in water and the soluble fraction was collected following centrifugation. This clear and soluble fraction was then evaluated for potential antibacterial activity and compared to the bacterial growth inhibition by Ampicillin. Colony forming assays demonstrated that the antibacterial properties of MBC tracked with the soluble fraction. 

To investigate if the antibacterial property of MBC was associated with small molecules, 100 mg of clay was suspended in water and placed in a dialysis tubing. This semipermeable membrane selectively allowed diffusion of molecules smaller than 12kDa. When this dialysis tubing containing clay was placed in a suspension of E.coli (gram-negative, a resident of small intestine, pathogenic) , the bacterial growth was strongly inhibited as assessed by CFU counts. This antibacterial effect however, was susceptible to the presence of EDTA, a reagent that chelates divalent metal ions. Remarkably, MBC’s antibacterial property was only partially blunted by EDTA, suggesting that other soluble small molecules in clay contributed to MBC’s antibacterial effects. Additional experiments revealed that MBC also inhibited the growth of Staphylococcus epidermidis, a gram-positive skin commensal, thereby demonstrating its broad-spectrum activity.  

These findings raise more questions than answered, setting the stage for additional research.  What is the biological mechanism underlying clay’s antibacterial properties? Is the antibacterial effect bacteriostatic or bactericidal? Immediate expansion of this project would focus on identifying metal-independent molecules in clay that exhibit antibacterial properties. This has a potential of identifying new molecules desperately needed for our war against superbugs.