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  • Germs check in, but they don’t check out

Jan 2009
Amanda D. Francoeur,

GAINESVILLE, Fla. – Small capsules that act like tiny roach motels catch and destroy even the most persistent and harmful bacteria. Researchers have conducted a study on a new antiseptic that may hold the potential to disinfect common household surfaces and medical instruments and even to destroy agents of bioterrorism such as anthrax. The research team is led by Dr. Kirk Schanze, a chemistry professor at the University of Florida, and Dr. David Whitten, a research professor in the department of chemical and nuclear engineering at the University of New Mexico in Albuquerque.

The capsules, ranging in size from 1 to 5 μm, are hollow and made up of two alternating layers of conducting polymers – one positively charged and the other negatively charged. A bacterium that comes in contact with a capsule is directed inside by fine polymer fibrils, or threadlike elements, attached to the capsule.

When exposed to light, the capsules absorb energy and transfer it to oxygen molecules that are located close by. The interaction forms an extremely toxic substance called singlet oxygen, which destroys the seized bacterium. “The bacteria are attracted to the spheres by a combination of electrostatic (charge-charge) and hydrophobic (water-hating) interactions,” Schanze said.

When kept in the dark for 10 minutes, a cluster of disinfecting capsules (green) has little interaction when combined with (red) P. aeruginosa bacteria (top). After an hour of exposure to white light, the capsules detained and destroyed 95 percent of the bacteria (bottom). The combination of heat from the capsules and nearby oxygen molecules formed singlet oxygen, which is extremely toxic to bacteria. Courtesy of the American Chemical Society.

For their study, the scientists tested the capsules with two strains of bacteria. The first was a comparatively safe form called Pseudomonas aeruginosa PAO1. Standard P. aeruginosa bacteria, which frequently are transferred via contaminated medical devices in hospitals, are dangerous germs that can seriously affect those with burns, cancer, AIDS and other ailments. The second strain was Cobetia marina, a nonpathogenic bacterium associated with marine equipment and ships.

After combining the capsules with either P. aeruginosa or C. marina, the researchers exposed the specimens to a fiber optic light source, and activity was monitored by confocal fluorescence microscopy. After about an hour of light exposure, testing revealed that more than 95 percent of both the PAO1 and C. marina bacteria had been destroyed. The findings were published online Nov. 24, 2008, in the American Chemical Society journal ACS Applied Materials & Interfaces.

These results demonstrate that the capsules could be especially helpful in developing coatings for medical devices that are particularly hard to keep sanitary. Heat or ultraviolet light can be used for sterilization in certain situations but not all. In addition, the capsules have been proposed as a method of killing gram-negative bacteria such as Escherichia coli and salmonella, which typically are especially resistant to antiseptics.

Schanze believes that the capsules could be effective enough also to sterilize hazardous biological agents such as anthrax. “In previous work, we have shown that the polymers that make up the capsules kill anthrax spores in a light-activated process,” he said. “So we expect that the capsules will have similar reactivity.”

Ultimately, with an increasing number of bacteria-related deaths – approximately 1.4 million resulting from bacteria attached to surfaces in clinics and hospitals – and with bacteria’s tendency to develop resistance to antibiotics, the tiny roach motels could prove to be a valuable resource in fighting the battle against lethal bacteria.

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