Six bangs and the bug’s out: light pulses as disinfectants

Intense light pulses can kill 99.999% of food poisoning bugs in just six bursts, say researchers from Strathclyde University today (Wednesday, 06 April 2005) presenting at the Society for General Microbiology’s 156th Meeting at Heriot-Watt University, Edinburgh.

The dangerous food poisoning bacteria Listeria monocytogenes can be effectively cleared from contaminated kitchen surfaces, water treatment plants, hospital operating theatres, and even from the air by using pulses of intense ultra-violet light, according to scientists from the Robertson Trust Laboratory for Electronic Sterilisation Technologies (ROLEST), based at the University of Strathclyde in Scotland.

The bursts of UV-rich light last just one millionth of a second each, but six pulses are enough to effectively disinfect an area, killing all but one in every hundred thousand bacteria. The researchers found that the way the bacteria were grown affected their susceptibility to the light pulses, with already stressed bacteria most likely to be killed.

Traditional methods of sterilising foods by using pasteurisation or chemical treatments are generally effective, but they can leave behind dangerously resistant bacteria. The new pulsed-light form of disinfection can kill food bugs very rapidly in exposed situations, if used at the right time in the bacteria’s development.

“Listeria can cause serious disease, especially during pregnancy or in people with weakened immunity, such as the elderly, sick or young children,” says Mohd Nizam Lani, who is undertaking PhD research in this area under the supervision of Professor John Anderson (microbiologist) and Professor Scott MacGregor (electrical engineer) at Strathclyde. “By developing a new method to control these bacteria we hope to help safeguard foods and protect consumers.”

The ability of the bacteria to survive exposure to UV light depended upon the way they were originally grown. The researchers found that Listeria monocytogenes also has a light repair mechanism, and some of the UV damaged bacteria could recover if they were later exposed to light of a longer wavelength.

The findings of the research open up new methods of preventing human illness, and will have important applications in catering, food and beverage handling, waste and water treatment, and hospital settings. In the clinical and healthcare sector, pulsed light may provide an effective treatment to destroy bacteria in the air and on surfaces in hospitals, helping to control the spread of hospital-acquired infections.