Charge-changing nanoparticles can help kill resistant bacteria

While the field of antibiotics has come a long way since the days of Louis Pasteur, the evolution of bacteria has created challenges for doctors trying to treat infections that have become largely drug-resistant. Researchers at MIT and Brigham and Women's Hospital may have found a solution: bombarding bacteria with antibiotics using nanoparticles that can evade the body's defenses.

In a paper published in ACS Nano, the researchers explain that while antibiotics strong enough to kill dangerous bacteria exist, getting them to the infection sites can be exceedingly difficult. So, they designed polymer nanoparticles to carry them, coated in nontoxic polyethylene glycol to help guide them toward infection and avoid getting flushed out by the body's immune system.

But that's not the novel part. The nanoparticles need to be positively charged in order to bind with the bacteria's negative charge, but, in practice, the immune system tends to detect and dispel positively charged materials before they can reach their target. The researchers' answer: Design the nanoparticles to change charges when they encounter bacteria.

The area around a bacterial infection is slightly acidic compared with the rest of the body, the researchers said, so they equipped the nanoparticles with a layer of pH-sensitive amino acids. When a particle veers into acidic territory, the molecule gains protons and flips its charge, allowing the polymer to bind to bacteria and release its antibiotic payload.

The researchers say they have a lot more work to do, but they're optimistic that applying nanotechnology to fighting bacteria could create new opportunities in the treatment of infectious diseases by overcoming resistance. "When bacteria are drug-resistant, it doesn't mean they stop responding; it means they respond but only at higher concentrations," said Aleks Radovic-Moreno, one of the paper's lead authors. "And the reason you can't achieve these clinically is because antibiotics are sometimes toxic, or they don't stay at that site of infection long enough."

- read MIT's story

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