Joined: 16 Mar 2004
|Posted: Tue Aug 25, 2009 8:44 am Post subject: White Paint and UV Light Kill Deadly Superbugs
Image credit: Annie Cavanagh and David McCarthy - Wellcome Image Awards 2008
Hospitals could tackle superbugs by painting walls and ceiling with a "killer paint" that destroys bacteria when exposed to light, if preliminary work by UK biochemists works out.
Tiny grains of titanium dioxide are used to give white paint its colour because it is very opaque, and very bright. But in 1985, biologists realised that titanium dioxide has more dangerous properties too, at least to bacteria.
Tadashi Matsunaga's team at the Tokyo University of Agriculture and Technology found that under UV light, microbes died on contact with a titanium dioxide-platinum compound.
Biologists later discovered that UV light excited electrons on the surface of titanium dioxide particles, and triggered a reaction with any water molecules on the particle surface.
The result is a potent mix of hydroxyl radicals and superoxide ions – reactive products that kill cells by degrading their membranes and letting their contents spill out.
Now Lucia Caballero and colleagues at Manchester Metropolitan University, UK, have set out to study whether white paint could be modified into a new weapon against superbugs in hospitals.
White paint typically contains around 20 to 30% titanium dioxide, combined with other additives such as calcium carbonate.
Caballero's team began by exposing samples of the bacterium Escherichia coli to paints containing no additives but high concentrations – up to 80% – of titanium dioxide. They also experimented with paints lower in titanium dioxide, but with paint additives such as calcium carbonate.
In the course of those experiments, they found that the paint additives can block the killer properties of titanium dioxide. "If calcium carbonate was present, the kill rate dropped by up to 80%," says Caballero. She thinks the additives block some titanium dioxide particles from becoming excited by UV.
The results suggest paint could be made into a bacteria killer by adding more titanium dioxide and removing fillers. But things are not so simple, Caballero says.
The reactive products made by exposing titanium dioxide to UV light draw no distinction between bacteria and any other substances. They attack and break down the acrylic emulsifier in the paint.
The Manchester researchers are currently considering possible ways to get around this.
Striking a balance between paint that is suitably deadly, but still long-lasting could prove difficult, thinks John Kiwi at the École Polytechnique Fédérale de Lausanne in Switzerland. Other approaches may be needed to solve the problem of bactericidal paints, he said.
Lucia Caballero presented her work at the Society for General Microbiology at Trinity College Dublin, Ireland, on 10 September.