Researchers from the Center for Food Safety, University of Georgia, have determined that blue light — which is commonly used to disinfect hospitals — destroys both dried cells and biofilms of the pathogen Listeria monocytogenes, a contaminant of food processing facilities.

According to the researchers, while L. monocytogenes has previously proven to be powerfully resistant to elimination, its destruction was expedited when the cells or biofilms of it were placed on polystyrene — a commonly used transparent plastic.

Electron micrograph of a flagellated Listeria monocytogenes bacterium, magnified 41,250X. Source: CDC/public domain

To make this determination, researchers placed liquid suspensions of mixtures of five strains of L. monocytogenes on sterile plates composed of six different materials — polystyrene, stainless steel and silicone rubber, among others — and then allowed to dry. Biofilms of L. monocytogenes on similar plates were also prepared.

Once dried, the researchers then shone blue light onto the biofilms and onto the dried suspensions of cells to discover which combinations of doses and wavelengths were most effective as well as the surface on which to most effectively eliminate the pathogens.

"The application of blue light for controlling microbial contamination has the potential to offer an additional technology that could complement existing methods for disinfecting surfaces in contact with foods," the researchers explained.

An article detailing the findings, “Inactivation of dried cells and biofilms of Listeria monocytogenes by exposure to blue light at different wavelengths and the influence of surface materials,” appears in the journal Applied and Environmental Microbiology.