Researchers have uncovered potent antimicrobial activity in a natural clay deposit found on the central coast of British Columbia, Canada. The research, published this week in mBio, an online open-access journal of the American Society for Microbiology, shows that the clay can kill members of the ESKAPE group of bacterial pathogens, the culprits behind some of the deadliest and most antibiotic-resistant hospital-acquired infections.
Kisameet clay, named for a nearby bay, has been used by the indigenous Heiltsuk First Nation people for several centuries to treat both internal and skin ailments. In the 1940s, doctors in Vancouver used the clay to successfully treat a variety of ailments such as ulcerative colitis, duodenal ulcer, arthritis, and burns. But, after antibiotics became widely available, the natural remedy was largely forgotten.
"We clearly need new antimicrobial agents," says Julian Davies, a microbiologist at University of British Columbia in Vancouver and senior researcher on the study. "Very few novel agents have been developed in recent years and we have increasingly multi-drug resistant strains appearing because of antibiotic overuse and misuse."
The ESKAPE group of bacteria includes pathogens such as MRSA, as well as those that cause pneumonia, urinary tract infections and septicemia. "These bacteria were identified as the leading problems in hospital-acquired infections because they are resistant to most antibiotics and are extremely difficult to treat," says Davies.
Davies and his graduate student Shekooh Behroozian wanted to determine if the clay harbored activity that could fight microbes in the lab. "When we started, we thought it was folk medicine, but it turned out to be much more than that," says Davies.
Using a collection of 16 bacterial strains mostly from local hospitals, Behroozian tested a diluted suspension of the clay for antibacterial activity against the strains. Incubating the bacteria with the clay suspension for 24-48 hours, the team showed that the clay had a strong antibacterial activity that killed all 16 strains.
Both water-based and solvent-based extracts of the clay also exhibit antibacterial activity. Extracts also killed Candida albicans, a pathogenic yeast, and prevented the formation of biofilms produced by two ESKAPE members, Staphylococcus aureus and Pseudomonas aeruginosa.
The exact mechanisms of how the clay kills bacteria and yeast are unknown, says Davies, largely because clay is a complicated mixture. Kisameet clay is about 24% by weight clay minerals, which are aluminum silicates with metal ions interspersed through their layers. Like soil, the clay also contains a complex microbial community. The clay's physical, chemical, and microbial properties are likely to contribute to its antimicrobial activity and may do so synergistically.
"It would be a dream to find isolates [from the clay] to make a new antibiotic," says Davies. But first, the clay and its extracts must be tested in animal models of bacterial infections to find out how it works and if it is a safe and effective treatment for moving forward to human trials.
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