The potential of violet, blue, green and red light for the inactivation of P. fluorescens as planktonic cells, individual cells on a surface and biofilms

Abstract Microbial contaminations are among the major health concerns worldwide. New innovative non-thermal technologies, such as photodynamic inactivation (PDI), are emerging as mild antimicrobial treatments. This research focussed on the effects of four different colours of visible light-emitting diodes (violet, blue, green and red, at 400, 470, 522 and 644 nm) on three different types of P. fluorescens contaminations: planktonic cells, individual cells on a surface and biofilms. The results demonstrated that only violet light inactivates planktonic P. fluorescens in a suspension (0.5-log reduction). Individual cells on a surface could be inactivated (i) effectively by violet light (3.7-log reduction in 30 min) when the cells were at optimal conditions and (ii) below the detection limit by both violet and blue light when salt stress was added to the environment. Finally, for the hydrated biofilms on polystyrene surfaces, no inactivation was achieved with any of the light sources. This study suggests that PDI is a promising technology for decontamination and preservation applications in the food industry where continuous lighting can be easily applied. It is considered more suitable as a technology to prevent microbial proliferation by intensive implementation than as a method to disinfect developed microbial populations.