Bio Focus: Light-activated quantum dots kill antibiotic-resistant superbugs
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ith the growth and spread of “superbugs,” bacteria resistant to multiple drugs, the world is quickly approaching a post-antibiotic era defined by incurable bacterial infections. To try to avoid this fate, researchers have devised alternative means to kill these hardy bacteria, such as using different types of nanoparticles, with varying degrees of success. In a major step toward this goal, scientists at the University of Colorado Boulder (UCB) have developed photoexcitable (light-activated) quantum dots that can effectively and specifically kill superbugs without harming mammalian cells. The semiconductor nanoparticles, described recently in Nature Materials (DOI: 10.1038/ NMAT4542), were able to kill 92% of multidrug-resistant bacteria in culture tests. “The problem of superbugs is current, it’s real, it’s alarming,” said study co-lead author Anushree Chatterjee, a chemical engineer at UCB. “We are out of antibiotics and we really, really need therapeutics that can work. This invention is important for this reason, and we have an extreme need to move forward to clinical trials.”
Light-activated cadmium telluride nanoparticle quantum dot (shown here in a highresolution transmission electron micrograph with a scale bar of 2 nm) designed to kill a number of multidrug-resistant bacteria without harming mammalian cells. Credit: Chatterjee and Nagpal labs, University of Colorado Boulder.
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MRS BULLETIN
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VOLUME 41 • MARCH 2016
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The overuse and misuse of antibiotics has recently led to a global epidemic of drug-resistant bacteria. In the United States alone, superbug infections affect nearly two million people and kill at least 23,000 each year, according to the Centers for Disease Control and Prevention. Some strains of bacteria, such as Neisseria gonorrhoeae (gonorrhea) and Klebsiella, are resistant to nearly all antibiotics, rendering them nearly untreatable. Various research groups have investigated nano-therapeutics—in particular, light-activated metal nanoparticles that destroy bacteria through heat or other means—as a replacement for antibiotics. While they are sometimes effective in killing superbugs, a common problem with these approaches is their non-specificity, or the propensity for the nano-therapeutics to be toxic to or damage mammalian cells. A different and promising approach with nano-therapeutics is to use them to attack superbugs with reactive oxidative species. Aerobic bacteria are able to mitigate or use free oxidative species to survive, but introducing specific oxidative species, such as superoxide radicals and peroxide, can disrupt the bacteria’s redox homeostasis and cause cell death; various antibiotics, such as ampicillin, gentamicin, and ciprofloxacin, are known to work through a similar process. While trying to develop intelligent, non-natural therapeutics to target antibiotic-resistant bacteria, Chatterjee teamed up with UCB chemical engineer Prashant Nagpal, co-lead author who was initially working on developing nanoelectronic techniques for single-molecule DNA and RNA sequenci
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