Abstract
Objective: This study investigates possible advantages in pulsed over continuous 405-nm light-emitting diode (LED) light for bacterial inactivation and energy efficiency. Background: Alternative nonantibiotic methods of disinfection and infection control have become of significant interest. Recent studies have demonstrated the application of systems using 405-nm LEDs for continuous disinfection of the clinical environment, and also for potential treatment of contaminated wounds. Methods: Liquid suspensions of 103 colony-forming units/mL populations of Staphylococcus aureus were subject to pulsed 405-nm light of different frequencies, duty cycles, and intensities and for different lengths of time. Results: Pulsed exposures with the same average irradiance of 16 mW/cm2 and varying duty cycle (25%, 50%, 75%) showed very similar performance compared with continuous exposures, with 95–98% reduction of S. aureus achieved for all duty cycles. The pulsing frequency was varied in intervals from 100 Hz to 10 kHz and appeared to have little effect on antimicrobial efficacy. However, when comparing pulsed with continuous exposure, an improvement in inactivation per unit optical energy was achieved, with results showing an increase of approximately 83% in optical efficiency. Conclusions: These results suggest that under pulsed conditions, a lower energy consumption and lower perceived brightness could be achieved, thus potentially providing improved operating conditions for medical/infection control applications without compromising antimicrobial efficacy.
Highlights
The antimicrobial effects of violet–blue light have been reported using wavelengths in the region of 400– 420 nm, with peak inactivation demonstrated at 405 nm.[1]
Control samples showed no significant change over the course of the experiments ( p ‡ 0.05). These results suggest that with the same dose applied over the same exposure time, the antimicrobial efficacy is not affected, either beneficially or adversely, when the light is applied in a pulsed rather than continuous regime
This study has indicated that pulsing of 405-nm light-emitting diode (LED) light, while maintaining the same dose over the same period of time, or varying the frequency, has similar performance when compared with the continuous exposure in terms of antimicrobial efficacy
Summary
The antimicrobial effects of violet–blue light have been reported using wavelengths in the region of 400– 420 nm, with peak inactivation demonstrated at 405 nm.[1] Absorption of this light by endogenous porphyrins results in the production of reactive oxygen species, including H2O2 and singlet oxygen, leading to oxidative damage and cell death.[2,3,4,5] Compared with ultraviolet (UV) radiation, 405-nm light offers reduced germicidal efficiency; it can be used at levels that are lethal to microorganisms,[1,6,7,8,9,10,11] without affecting exposed mammalian cells.[12,13,14]. Pulsed operation of UV light-emitting diodes (LEDs) has reportedly resulted in improved antimicrobial efficacy[19,20]; it is of interest to investigate whether the same principle can be applied to 405-nm light
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