Antibiotic resistance has been described by the World Health Organization as a “global health security threat.” In the United States alone, over 2 million people become infected with bacteria that are resistant to multiple drugs, known as “superbugs.” A recent study led by Lynda Williams of Arizona State University suggests that minerals found in clay deposits might be a good source of antibiotics that can combat superbugs. The findings were published in the journal Environmental Geochemistry and Health.

"As antibiotic-resistant bacterial strains emerge and pose increasing health risks," Williams stated in a press release, "new antibacterial agents are urgently needed.”

Humans have been applying clay to wounds for millennia, long before any knowledge of pathogens or antibiotics existed. Williams published a paper in 2012 that explored the antibiotic potential of two French green clays rich in iron smectite when in contact with Buruli ulcers. The infections are caused by Mycobacterium ulcerans that causes a necrotic lesion which can lead to disability or death if left untreated. Though the clay was effective at killing the bacteria, the deposit became used up and a suitable replacement was difficult to find.

This recent research explored the antibiotic efficacy of clay from a deposit in the Crater Lake region in Oregon. The clays in this area were likely formed 20-30 million years ago and have incorporated deposits of volcanic ash, including that from the eruption of Mt. Mazama about 7,700 years ago. There were four types of clays sampled from this region: two blue, one white, and one red.

Both blue clay samples completely eliminated superbugs methicillin-resistant S. aureus (MRSA) and extended-spectrum beta lactamase (ESBL) E. coli, along with several other bacteria. The white clay was also effective against E. coli and S. epidermidis, but the red did not demonstrate any significant antibiotic properties.

"To date, the most effective antibacterial clays are those from the Oregon deposit,” Williams stated.

Williams and her team were able to learn more about the mechanism that fights these infectious bacteria, supporting their previous research with the French deposits. Skin typically has a pH below 5.0, making it slightly acidic and helps to keep bacteria in check. However, chronic wounds are usually more alkaline.

"Antibacterial clays can buffer wounds to a low pH," Williams explained. "The clays may shift the wound environment to a pH range that favors healing, while killing invading bacteria."

Additionally, the minerals within the clay uptake iron too rapidly, which was too much for the iron-storing proteins within the bacteria to handle. As the iron oxidizes, it creates molecules that damage the cell and kill the bacterium. While there are currently available wound treatments that make the lesion more acidic to help kill bacteria, understanding more about how the task is accomplished could lead to the development of new topical treatments that fight drug-resistant superbugs.