Attacking MRSA with metals from antibacterial clays

May 17, 2013

In the race to protect society from infectious microbes, the bugs are outrunning us. The need for new therapeutic agents is acute, given the emergence of novel pathogens as well as old foes bearing heightened antibiotic resistance.

Shelley Haydel, a researcher at Arizona State University’s Biodesign Institute and associate professor in the School of Life Sciences, has a new approach to developing effective, topical antibacterial agents – one that draws on a naturally occurring substance recognized since antiquity for its medicinal properties: clay. Download Full Image

In research appearing in the journal PLOS ONE, Haydel and her graduate student, Caitlin Otto, lay out the case for clay, demonstrating that certain varieties of clay have the ability to aggressively kill a range of pathogens including E. coli and methicillin-resistant Staphylococcus aureus (MRSA) – a stubborn, highly contagious and dangerous pathogen that has lately been the scourge of many hospitals, and is a common cause of skin infections in the community. Their study further indicates that, rather than the physical particles of the clays, particular metal ions attached to the clay are likely responsible for its potent antibacterial properties.

“While some natural clays, which have absorptive properties similar to sponges, have been used topically for centuries, scientific studies investigating the antibacterial mechanisms represent a relatively new area of research,” Haydel says. “With this study, we have demonstrated that the antibacterial activity of these natural clays is not dependent on the physical clay particles, but rather the abiotic, microbicidal activities of specific metal ions desorbed from the clay surface. While we are still working on a mechanism of action studies, determining that specific metal ions influenced antibacterial activity was critical in leading us in the appropriate scientific directions.”

Medical use of clay has a storied history. As early as 5,000 years ago, clay was listed in the ancient tablets of Nippur as a wound-healing medicament. Around 1600 BC, the Ebers Papyrus – recognized as the world’s oldest medical text – recommended clay for ailments including diarrhea, dysentery, tapeworm, hookworm, wounds and abscesses. Clays came into common use in the 19th century as topical treatments for surgical wounds, demonstrating their beneficial effects for pain management, inflammation, putrefaction and healing processes.

In their current study, Otto and Haydel examined four clay samples and their respective aqueous mineral extracts or leachates and determined that the clays exhibited different in vitro antibacterial activities against E. coli and MRSA. Mineralogically, the samples were nearly identical with 52 percent clay and 48 percent non-clay minerals, but the composition of metal ions released from the mineral surfaces varied considerably across the samples. The tests, using aqueous mineral leachates of the four clay samples, uncovered a variety of elements in varying concentrations. Based on previous studies, the research team focused on five metal ions – iron (Fe), copper (Cu), cobalt (Co), nickel (Ni) and zinc (Zn).  

When non-antibacterial clays with low concentrations of these five critical metal ions were supplemented with higher amounts and the pH was matched with that of antibacterial clays, the new formulation displayed killing ability against E. coli and MRSA. The result pointed to the presence of metal ions in sufficient concentration as the antibacterial agent in the clay. Further tests narrowed the field of antibacterial candidates, establishing Fe+2, Cu+2 and Zn+2 ions as contributing antibacterial agents.

While the pH level was found to play a mediating role, the lethal effect of the clays could not be attributed exclusively to pH, absent in the influence of metal ions. Metal speciation modeling and statistical analysis of the results indicated that Cu+2, Co+2, Ni+2 and Zn+2 are effective against E. coli, while Cu+2, Co+2 and Zn+2 are effective against MRSA. Intriguingly, the study found that the metal ion toxicity of a given clay sample is not always proportional to the total ion concentration. Toxicity instead is critically dependent on a variety of other factors including pH, ion solubility, osmotic strength and temperature. The tests undertaken helped to evaluate the interplay of these factors in determining both the antibacterial effectiveness and toxicity of the samples.

Haydel notes that physical and chemical properties of minerals contained in clays together contribute to healing properties. Minerals contained in clay mixtures have a negative surface charge that allows the free exchange of compounds from the environment, including bacteria, viruses, proteins, nucleic acids and cations. Kaolinite, talc and smectite clay minerals are highly absorptive. Due to their ability to adhere to the skin, clays offer mechanical protection similar to a bandage, sealing out external physical or chemical agents, as well as absorptive properties which assist in removing devitalized tissue, particulate matter or foreign materials from a wound.

Haydel is optimistic about the potential for medicinal clays to play a greater therapeutic role, particularly against the growing threat of topical and antibiotic-resistant infections:

“We have demonstrated that mineralogically-identical clays exhibit chemical variability which correlates with variability in antibacterial activity. 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.”

Shelley Haydel is an associate professor in the School of Life Sceinces (SOLS) and recently received the SOLS Teaching Excellence and Innovation Award.

Caitlin Otto recently received an ARCS Scholar Award from the Advancing Science in America Foundation Phoenix Chapter.

Richard Harth

Science writer, Biodesign Institute at ASU


ASU recognizes outstanding teen research at Intel Science and Engineering Fair

May 17, 2013

Last week, the rooms of the Phoenix Convention Center were lined with booths and panels showcasing innovative student research from around the world.

Renowned as the world’s largest pre-college science competition, the Intel International Science and Engineering Fair (ISEF) came to Phoenix May 12-17 in an effort to inspire and empower teens to become tomorrow’s innovators in the field of research. Intel ISEF Competition Download Full Image

ASU’s Office of Knowledge Enterprise Development (OKED) partnered with the Provost’s Office to offer Special Awards to outstanding students at ISEF.

“This is a prime opportunity for ASU to learn about the activities of these students, and for them to learn about ASU's emphasis on integrating use-inspired research into its learning environment and directing our entrepreneurial attention towards solving society's problems,” said William Petuskey, associate vice president of science, engineering and technology for OKED. “While ASU is pleased to recognize some of the ISEF finalists with awards, it salutes all of the students for the extraordinary high quality of their work and presentations.”  

Every year, approximately 1,500 high school students from 70 countries, regions and territories gather to solve problems through independent research. This year, Arizona saw 20 of its high school students hosting expo booths and competing for scholarships.

ASU joins organizations such as NASA and Google in recognizing individual student research through Special Awards such as scholarships.

This year ASU played a key role by providing volunteer judges in the form of ASU faculty and senior-level graduate students who were qualified and eager to inspire the future generation of scientists and engineers. Judges were required to have a doctorate or master’s degree with six years of relevant experience. These judges were tasked with selecting students for ISEF Grant Awards across 17 different science and engineering categories.

For William and Lorna Glaunsinger, co-chairs of the judging committee for this year’s Grand Awards, the fair is one that they happily returned to after its first appearance in Phoenix in 2005.

“One of the reasons we’re involved is that any time this fair comes to the state, there is an improvement in education that comes along with it,” said William Glaunsinger. “It sets a standard of achievement because of the huge impact it has on the schools in the area.”

Looking toward the future, the Glaunsingers are conscious of the challenges that are in store for future conferences in regards to recruiting judges, maintaining innovative topic ideas and raising local awareness for the fair.

“We are always looking at being on the cutting edge of science in terms of our categories,” said Lorna Glaunsinger. “Things are constantly changing in this field and we’re seeing a mixing of knowledge in regards to the different disciplines.”

ASU’s Office of Knowledge Enterprise Development, in partnership with the Provost’s Office, also offered Special Awards to 29 students. Award packages included four-year scholarship Provost’s Awards in addition to a research stipend for students who choose to attend ASU. The list of Special Award recipients may be found online at

The Global Institute of Sustainability’s Rob and Melani Walton’s Sustainability Initiatives also supported scholarships to students whose projects demonstrated excellence in the field of sustainability.

ASU’s contribution to Special Awards together constituted one of the largest awards offered at the competition, and represents the university’s commitment to support the goals and mission of ISEF.

Student winners of this year’s New American University Provost Scholarship include in-state students Tejas Dharmaraj, 15, and Manav Ajay Sevak, 16, both students at Chandler High School.

Dharmaraj and Sevak won for their project “Indicting Alzheimer's: Novel Methods of Preventing Glial Scarring through the Downregulation of Cerebral Vimentin and Glial Fibrillary Acidic Protein.”

Additional in-state winners include Kelsey Mackenzie Barter, 17, of University High School in Tucson.

Barter was awarded the scholarship for her research on cancer treatment, titled, “Targeting Survivin as a Potential Cancer Therapeutic.”

In addition to hosting expo booths and symposiums, ASU held a discussion about its new online research platform, Quanta. Launching in the fall of 2013, Quanta is a new program geared toward engaging high school students in research and creating an online social community that encourages passion in various research fields.

Begun as a student-led program in 2011, Quanta initially set out to promote careers in the fields of science, technology engineering and mathematics (STEM) to high school students while simultaneously providing access to university experiences and resources through university mentors.

Quanta encourages high school students, college students and research professionals alike to participate in the program, which allows them to collaborate with and mentor one another in programs focused on fostering sustained involvement in research.

The Intel ISEF Competition will return to Arizona in 2016 and 2019. The Office of Knowledge Enterprise Development, the Global Institute of Sustainability and other groups at ASU also plan to continue their presence at the fair for the upcoming 2014 Intel ISEF in Los Angeles.

Written by Lorraine Longhi