Superbugs may meet their match in these nanoparticles

Antibiotics may have a new teammate in the fight against drug-resistant infections.

Researchers have engineered nanoparticles to produce chemicals that render bacteria more vulnerable to antibiotics. These quantum dots, described online October 4 in Science Advances, could help combat pathogens that have developed resistance to antibiotics (SN: 10/15/16, p. 11).

“Various superbugs are evolving too rapidly to be counteracted by traditional drugs,” says Zhengtao Deng, a chemist at Nanjing University in China not involved in the research. “Drug-resistant infections will kill an extra 10 million people a year worldwide by 2050 unless action is taken.”

In the study, antibiotics spiked with quantum dots fought off bacteria as effectively as 1,000 times as much antibiotic alone. That’s “really impressive,” says Chao Zhong, a materials scientist at ShanghaiTech University who was not involved in the study. “This is a really comprehensive study.”

Quantum dots, previously investigated as a tool to trace drug delivery throughout the body or to take snapshots of cells, are made of semiconductors — the same kind of material in such electronics as laptops and cell phones (SN: 7/11/15, p. 22). The new quantum dots are tiny chunks of cadmium telluride just 3 nanometers across, or about as wide as a strand of DNA.

When illuminated by a specific frequency of green light, the nanoparticles’ electrons can pop off and glom onto nearby oxygen molecules — which are dissolved in water throughout the body — to create a chemical called superoxide. When a bacterial cell absorbs this superoxide, it throws the microbe’s internal chemistry so off-balance that the pathogen can’t defend itself against antibiotics, explains study coauthor Anushree Chatterjee, a chemical engineer at the University of Colorado Boulder.

Chatterjee and colleagues mixed various amounts of quantum dots into different concentrations of each of five antibiotics, and then added these concoctions to samples of four drug-resistant bacterial strains, such as Salmonella. More than 75 percent of the 271 tested antibiotic and quantum dot combinations were better at killing or curbing the growth of bacteria than antibiotics would have been alone.  

One limitation of this treatment is that the green light that activates the nanoparticles can shine through only a few millimeters of flesh, says coauthor Prashant Nagpal, a chemical engineer also at the University of Colorado Boulder. So these quantum dots could probably be used only to treat skin or accessible wound infections.

The researchers are now designing nanoparticles that absorb infrared light, which can pass through the body. “That could be really effective in deep tissue and bone infections,” Nagpal says.

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Editor’s note: This story was updated October 25, 2017, to correct details about the tests of quantum dot-antibiotic combinations against drug-resistant bacterial strains.