Iron-bearing clay shows antimicrobial, anti-biofilm effects
Researchers have identified some naturally-occurring clays that demonstrate antimicrobial properties, including some that kill many antibiotic-resistant pathogens. That is a finding they say could be an avenue to new approaches to wound treatment.
Published online ahead of print in International Journal of Antimicrobial Agents (Aug. 1, 2018), the study evaluated the effects of an iron-bearing clay found in Oregon against staphylococci, streptococci, Enterobacteriaceae and non-fermenting Gram-negative bacilli.
“Working with Mayo Clinic (Rochester, Minn.), we showed that these clays also diminish populations of bacterial biofilms, as well as bacteria common in wounds that are more resistant to drugs,” said study co-author Lynda Williams, PhD, in a press release. Dr. Williams is a biogeochemist at Arizona State University in Phoenix. “The results support our efforts to design new antibacterial drugs using natural clays.”
Researchers unearth a natural clay deposit with antibacterial activity. Photo by: Lynda Williams, Arizona State University
In the study, the clay and its aqueous leachate were evaluated against the bacteria in biofilm and planktonic states. Investigators used time-kill studies to assess the antimicrobial activity against the microbes in their planktonic. Biofilms on medical-grade Teflon discs were treated with a hydrated clay suspension or leachate.
The researchers found that both the clay and the leachate exhibited bactericidal activity against almost all the microbial strains in their planktonic state, with the exceptions of the leachate not showing activity against either S. aureus IDRL-6169 or S. aureus USA300.
All but two of the microbial strains treated with clay suspension and leachate resulted in statistically significant biofilm population reductions compared with controls, with the exceptions again being S. aureus IDRL-6169 and S. aureus USA300 (p<0.05).
In the press release the authors note that biofilms occur in two-thirds of wounds seen by healthcare providers, and increase the resistance of the involved bacteria to antibiotics.
“We showed, however, that this reduced iron-bearing clay can kill some strains of bacteria under the laboratory conditions used, including bacteria grown as biofilms, which can be particularly challenging to treat,” said lead author Dr. Robin Patel, in the release. Dr. Patel is an infectious disease physician and clinical microbiologist at the Mayo Clinic in Rochester, Minn.
The investigators emphasize that this research is preliminary, and they only tested one concentration of the clay suspension. They also say that not all types of clay are beneficial.
These lab tests are just one step in simulating the complex environment of an infected wound. More research is needed to identify and reproduce the properties of clays that are antibacterial, with the goal of synthesizing a consistent compound of the clay minerals under quality control, investigators note in the release.
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