Inactivation of Bacteria Using Single Wavelength 405 nm Light

Introduction: Vital Vio LLC of Troy, NY has developed a system containing light emitting diodes that give off a single wavelength of light at 405 nm. This is a visible form of light that is near the border between visible and ultraviolet light. This wavelength of light is capable of producing “reactive oxygen species” (ROS) within bacteria that leads to cell death.

Purpose: This study tested the efficacy of bacterial inactivation over time using a continuous 405 nm light source.

Methods: Glass slides were coated with equal volumes of a bacterial suspension (Staphylococcus aureus or Pseudomonas aeruginosa). The dried slides were placed on shelves that were two and eight feet from the light source. On the opposite side of the experimental set up there were two shelves at the same height intervals that contained an equal number of bacteria-coated glass slides, but the light source was from fluorescent fixtures on the ceiling of the laboratory (controls). Triplicate samples from each shelf (treatment and controls) were collected at times: 0, 0.5, 1, 2, 4, 7, 14, 21, 28, and 35 days for Staphylococcus aureus and 0-28 days for the Pseudomonas aeruginosa.The concentration of live bacteria on each slide was determined by classical methods of serial dilution and plating onto a standard growth medium.

Results: There was a small (0.5-2 log) but statistically significant (95% confidence interval) difference between the bacteria exposed to the 405 nm light and the ambient light for the Staphylococcus aureus, while Pseudomonas aeruginosa analyses yielded mixed results with regards to statistically significant differences.

Significance: The combination of continuous exposure to low-level biocidal light plus episodic cleaning/sanitizing of food-related surfaces can improve pathogen control.