Death by a thousand cuts: how antibacterial clays kill

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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

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Saving brains: malaria in pregnancy leads to cognitive deficits in offspring

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The malaria clinic at Nalufenya Children’s Hospital in Jinja, Uganda (Credit: Chloe McDonald)

In the global effort to eradicate malaria, the focus has often been on the number of lives saved—through insecticide-treated bed nets, artemisinin-based therapies, vector control and other strategies. Equally important in this fight is the concept of saving brains, particularly in young children.

Malaria is caused by an infection with the parasite Plasmodium falciparum and can manifest as either an uncomplicated or severe disease. The most severe neurological complication is cerebral malaria, a disease that disproportionally affects young children because they have not yet developed immunity against Plasmodium parasites. More than 785,000 children under the age of nine living in sub-Saharan Africa are affected by cerebral malaria each year. The idea of saving brains becomes especially relevant in this population because cerebral malaria can have long-lasting effects on the cognitive function of these children. An early study found that children who developed cerebral malaria were roughly three and a half times more likely to have a cognitive deficit than children who did not have malaria. Importantly, researchers observed this difference two years after the initial episode of cerebral malaria and long after the disease itself had been treated.

If exposure to malaria at a young age could have long-lasting effects on the cognitive abilities of children, what happened when that exposure happened much earlier? Like during pregnancy? In a new study published in PLoS Pathogens, a team of researchers led by Dr. Chloë McDonald and Dr. Kevin Kain showed that malaria in pregnancy leads to cognitive impairments in the offspring that persist into adulthood. Continue reading

Phages fight back: how anti-CRISPRs interfere with the bacterial immune system

A transmission electron micrograph of phage JBD93, which contains an anti-CRISPR gene. (Credit: Joe Bondy-Denomy)
A transmission electron micrograph of phage JBD93, which contains an anti-CRISPR gene. (Credit: Joe Bondy-Denomy)

So nat’ralists observe, a flea
Hath smaller fleas that on him prey;
And these have smaller fleas to bite ‘em.
And so proceeds Ad infinitum.

Jonathan Swift, 1733

When the Anglo-Irish satirist wrote these words nearly two centuries ago, he could not have known just how far down the tree of life his observations would hold true. These predator-prey relationships exist beyond the plains of Africa or the jungles of Borneo. They extend to the realm of microscopic organisms and to the world of bacteria and the teeny tiny, itsy bitsy viruses that prey on them. These viruses are called bacteriophages, or phages for short.

Like human and other animal viruses, phages rely completely on their host for reproduction. They enter a bacterial cell and hijack the cellular machinery to make new phages until the cell is literally bursting with viral cargo. A torrent of phages is unleashed that go on to infect more bacteria and continue the cycle.

But bacteria are not helpless victims in this story. They have a large arsenal of anti-phage weapons to keep phages out and prevent them from taking over. Perhaps the coolest of these weapons is the CRISPR-Cas system. First discovered in 2007, the CRISPR-Cas system functions as the bacteria’s immune system. It is both a memory keeper and a hitman. Every time a bacteria survives a phage infection (which doesn’t happen often), the CRISPR-Cas complex takes a small piece of phage DNA and adds it to the bacteria’s own DNA, gradually building a database of unique DNA fingerprints from every phage that has ever tried to kill it. In other words, bacteria with CRISPR-Cas systems are able to “learn” from their previous phage encounters and acquire immunological memory based on those experiences—a trait that was previously thought to be unique to animals.

“It’s the first example of a single cell, simple [bacteria] having an adaptive immune system,” says Dr. Joseph Bondy-Denomy, a faculty fellow at the University of California, San Francisco. “The adaptability of CRISPR is very, very rapid. I think that’s why it’s so exciting.” Continue reading