Photoinactivation of Escherichia coli by 405 nm and 450 nm light-emitting diodes: Comparison of continuous wave and pulsed light

Background: Antimicrobial blue light (ABL) therapy is one of the novel non-antibiotic approaches and recent studies showed the potential of pulsed ABL.Purpose: Comparing photoinactivation effect of continuous wave (CW) and pulsed blue light and investigating the impact of varying light parameters.Methods: E. coli cells in planktonic were treated with CW and pulsed light (405 nm and 450 nm) at 60 mW/cm2, and the samples were taken to assess survival, reactive oxygen species (ROS) level, damage of cell membrane and metabolic activity. Further, a ROS scavenger was used to find the role of ROS played in ABL therapy. Results: E. coli was more sensitive to 405 nm light and the photoinactivation was dose-dependent. Pulsed 405 nm light showed the better antimicrobial effect on E. coli and caused increasing damage of cell membrane. It might be attributed to the ROS production in bacteria.Conclusion: Pulsed light has a potential of improving the efficacy of ABL therapy and is worth to be explored deeply further.