Seeing the light: Exploring the potential of visible light as a means of controlling listeria monocytogenes in the food chain

The ability of Listeria monocytogenes to withstand processes employed by the food industry to inhibit or limit bacterial growth has become a major health and economic problem worldwide. The bacterium's survival is due, in part, to the action of the alternative sigma factor σ^B . This alternative transcription factor is responsible for regulating defence mechanisms in response to stresses such as extremes of temperature, osmotic, acid and ethanol stress, as well as contributing to virulence. Recently, light therapies have been proposed as additional means for the control of contamination, with applications focused on the food and medical device industries. Several variations of light treatment are currently being investigated, among them UV light therapy and photodynamic inactivation therapies. While these therapies are not limited solely to the management of L. monocytogenes, the discovery of the blue light photoreceptor Lmo0799 upstream of the Listerial σ^B activation cascade has resulted in increased interest in the effects of light on L. monocytogenes. This chapter reviews the mechanisms by which light is known to stimulate the σ^B activation cascade, and light treatments currently being investigated as suitable regimes for management of contamination. A detailed understanding of the mechanisms by which light influences virulence and the stress response in L. monocytogenes, as well as the mechanisms by which light causes cellular damage, is key for the successful development of new light-based control measures.