Researchers at Arizona State University’s Biodesign Institute have published a study that lends some merit to the colloquial first aid advice to "rub some dirt in it."
Associate professor Shelley Haydel and graduate research associate Caitlin Otto looked into the practice and found a family of antibacterial clays capable of killing pathogens ranging from E. coli to methicillin-resistant Staphylococcus aureus, otherwise known as hard-to-kill MRSA.
Clays have been used since antiquity for wounds, in poultices and in baths. Clays were ingested to treat diarrhea, dysentery, tapeworm and hookworm. In the 19th century, clays were applied to surgical wounds to reduce inflammation and putrefaction, and to aid healing and pain management.
Researchers tested a variety of different clays and found that five metal ions -- iron, copper, cobalt, nickel and zinc -- had antibacterial properties when present in sufficient quantities with an acceptable pH. The study, published in the journal PLoS ONE, also identifies the specific ions which are effective against E. coli and MRSA.
Haydel is optimistic about the potential for medicinal clays in the fight against antibiotic-resistent pathogens. Currently, MRSA is highly contagious and often plagues hospitals.
The authors also suggest more widespread use for the clay, particularly as bandages. The clays adhere to the skin to seal out external contaminants, and their absorptive properties help remove devitalized tissue and foreign materials from a wound, while the antiseptic metal ions prevent infection.
Haydel notes that many minerals found in clays are toxic. "Since clays can contain toxic metals, such as arsenic, cadmium, lead, and mercury, safety precautions must be in place to minimize exposure to toxic ions. Efforts must be taken to standardize the composition and antibacterial efficacy of clays if they are to be used therapeutically and prophylactically."