Polymers Help Researchers Form New Antibiotics

Scientists have developed a method using nanoparticles laced with polymers that promises to deliver potent antibiotics directly to bacteria. The method would bypass the body’s natural resistance to certain designer drugs, and combat bacteria that have grown resistant to existing drugs.

A team of researchers built the nanoparticles from a polymer coated with polyethylene glycol, commonly used to deliver drugs within the body because it is nontoxic, writes Infection Control Today. The polymer also is known for its ability to travel through the bloodstream without being detected by the immune system.

An advantage that the nanoparticles have is that they can switch their charge depending on the environment. Previously used nanoparticles were designed to have a positive charge, which is attracted to bacteria’s negatively charged cell walls. However, the body’s immune system tends to clear positively charged nanoparticles from the body before they encounter the bacteria.

Because the new nanoparticles can switch charges, they move in the bloodstream with a negative charge. But when they reach the infection site, they change to a positive charge, allowing them to bind to the bacteria and release the drug.

The environment surrounding bacteria is slightly acidic. Often, antibiotics lose their effectiveness as acidity increases, but the scientists found that their antibiotics carried by the nanoparticles kept their potency better than traditional antibiotics.

The antibiotics release their drug payload over a one- to two-day period. “You don’t want just a short burst of drug because the bacteria can recover once the drug is gone,” says Aleks Radovic-Moreno, an MIT graduate student and one of the researchers, who was the lead author of a paper describing the nanoparticles in the journal, ACS Nano. “You want an extended release of drug so that bacteria are constantly being hit with high quantities of drug until they’ve been eradicated.”

Further research will continue, but the researchers hope that the high doses that can be delivered by the nanoparticles will help overcome bacterial resistance. “When bacteria are drug resistant, it doesn’t mean they stop responding, it means they respond but only at higher concentrations. 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,” Radovic-Moreno says.

Source: “Engineers Design Nanoparticles that Deliver High Doses of Antibiotics Directly to Bacteria,” Infection Control Today, 5/4/12
Image by NIAID/RML, used under Fair Use: Reporting.