Death by a thousand cuts: how antibacterial clays kill

OMT blue clay
A section of blue clay from the open pit mine at the Oregon Mineral Technologies clay deposit near Crater Lake. The antibacterial blue clay is surrounded by white clay which lacks antibacterial properties. (Credit: Keith Morrison)

By now most of you will have heard that more and more bacteria are becoming impervious to the many life-saving antibiotics on which we’ve come to rely. In November, scientists in China sampling bacteria from meat and hospitalized patients found a new gene called MCR-1 that confers resistance to colistin, a drug that is currently used as a last resort when all other antibiotics have failed. This report was the latest in a series of increasingly worrisome news that have spurred researchers to look for new ways to combat antimicrobial resistance. While some scientists are exploring futuristic ideas like light-activated nanoparticles, others are looking to nature and literally digging up dirt for inspiration.

In a paper published recently in Scientific Reports, researchers have revealed for the first time the mechanism behind the antibacterial properties of medicinal clay.

“People have been eating clays for thousands of years,” says Dr. Keith Morrison, the report’s lead author and now a postdoctoral fellow at the Lawrence Livermore National Laboratory. The purported benefits of eating clay relate to its ability to grab heavy metals and other “toxins” and expel them from your body. However, the scientific evidence supporting this idea (and the idea that our bodies need any detoxing at all) is lacking.

As a PhD student at Arizona State University, Morrison was interested in another curious property of some medicinal clays—their ability to kill bacteria. While the use of clay to treat wounds and skin infections can be traced back to the 19th century, the scientific study of these antibacterial clays is a fairly new field. Continue reading

Too hot to handle: investigating birds’ heat tolerance sheds light on their ability to adapt to climate change

A Gambel’s quail (Credit: Dick Daniels. CC BY 3.0)

In January 2014 more than 100,000 megabats died in the Australian state of Queensland. The cause? Heat.

That summer, a heatwave passed through Queensland causing temperatures to reach highs of nearly 45°C (113°F). Unable to cope with the extreme heat and subsequent dehydration, megabats, or flying foxes as they’re known locally, started dropping from the sky. On one extremely hot day, researchers recorded at least 45,500 dead bats in southeast Queensland.

“Most of the stuff you read about on climate change [talks about] average monthly temperature or average annual temperature rising by two degrees. But what’s also going to happen is the occurrence of extreme events is going to increase—in frequency and in intensity,” says Dr. Alex Gerson, an assistant professor in the department of biology at the University of Massachusetts, Amherst. “So what’s a desert going to look like in 100 years? Is it going to be devoid of birds completely or is something going to be able to make it?” Continue reading

Asymptomatic dengue-infected humans can transmit the virus to mosquitoes

A drawing of a female Aedes aegypti mosquito (Credit: E.A. Goeldi)

An estimated 3.9 billion people in 128 countries are at risk of dengue virus infection. Of the estimated 390 million dengue infections that occur each year, 96 million will manifest clinically with flu-like symptoms including fever, headache, nausea and muscle and joint pain. Unlike the flu virus, dengue virus cannot be transmitted directly from person to person. It instead relies on an insect vector, the mosquito Aedes aegypti. Female mosquitoes contract the virus when they bite and feed on an infected human. After a period of four to ten days, the virus disseminates to various tissues in the mosquito, where it remains for the rest of the mosquito’s life. At this point, the mosquito is infectious and can transmit the virus through its saliva and bite.

Earlier studies showed that the time during which dengue virus-infected humans can transmit the virus to mosquitoes coincides with the onset of clinical symptoms and an increase in viral load in their blood. These observations led to the assumption that infected, asymptomatic humans are so-called “dead-end hosts” for the virus because their viral levels are so low as to make them noninfectious to mosquitoes, essentially breaking the transmission chain.

In a new paper published last week in the Proceedings of the National Academy of Sciences, an international group of researchers challenged a long-held assumption that asymptomatic patients infected with the dengue virus are not infectious. The team sought to experimentally test the assumption that asymptomatic people are noninfectious and to determine how human-to-mosquito transmission varied with timing of symptom onset. Continue reading