Scientists at MIT and Tufts University have too--and they're doing something about it. They've demonstrated that covalent attachment of N-alkylated poly(4-vinylpyridine) (PVP) to glass surfaces makes the surfaces lethal to several types of bacteria on contact [Proc. Natl. Acad. Sci. USA, 98, 5981 (2001)].

Several other research groups have shown that PVP and other polycationic polymers in solution can kill bacteria by disrupting bacterial cell membranes, and efforts have been made to immobilize such compounds. But immobilization always seemed to render the polymers totally inactive.

Postdoc Joerg C. Tiller, visiting scientist Chun-Jen (Jason) Liao, and professor of chemistry and bioengineering Alexander M. Klibanov at MIT, along with associate professor Kim Lewis at Tufts's Biotechnology Center, have now found a fairly narrow range of N-alkylated PVP compositions that allow the polymers to retain their bacteria-killing ability when coated on dry surfaces. These are the first engineered surfaces that have been shown to kill airborne microbes in the absence of any liquid medium.

Previous efforts to design dry bactericidal surfaces were unsuccessful, the researchers hypothesized, because the polymer chains weren't sufficiently long and flexible to penetrate bacterial cell walls. Their polymer includes a long linker that enables the toxic N-alkylated pyridine groups to cross the bacterial envelope.

Alkyl chain length also proved to be important. Dry surface-bonded PVP with either no N-alkyl chains or long N-alkyl chains (10 or more carbon units) is not bactericidal. But three- to eight-unit PVP chains have sufficient positive charge (from the cationic pyridine nitrogen) to repel each other and stay flexible and sufficient hydrophobicity to penetrate bacterial cell walls.

Such surfaces kill 94% to more than 99% of bacteria sprayed on them. And because the coating is chemically bonded to the surface, it doesn't wash off.

Chemical engineering professor Jonathan S. Dordick of Rensselaer Polytechnic Institute notes that the surface treatment is potentially long-lasting and capable of being scaled up to commercial production at moderate cost. "It's elegant in that it simply involves applying a certain molecule as a paint or coating," Dordick says, "and coating technologies are pretty advanced, so it's not hard to do."

Klibanov says his group now hopes to demonstrate "that you can take any common surface--whether it's polyvinyl chloride, polyethylene, metals, ceramics, wood, fabrics, or whatever--and use this kind of derivatization to make that surface capable of killing airborne bacteria. We also want to elucidate the mechanism of how this bacterial killing takes place."

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