Low-level red laser therapy alters effects of ultraviolet C radiation on Escherichia coli cells

Abstract

Low-level lasers are used at low power densities and doses according to clinical protocols supplied with laser devices or based on professional practice. Although use of these lasers is increasing in many countries, the molecular mechanisms involved in effects of low-level lasers, mainly on DNA, are controversial. In this study, we evaluated the effects of low-level red lasers on survival, filamentation, and morphology of Escherichia colicells that were exposed to ultraviolet C (UVC) radiation. Exponential and stationary wild-type and uvrA-deficientE. coli cells were exposed to a low-level red laser and in sequence to UVC radiation. Bacterial survival was evaluated to determine the laser protection factor (ratio between the number of viable cells after exposure to the red laser and UVC and the number of viable cells after exposure to UVC). Bacterial filaments were counted to obtain the percentage of filamentation. Area-perimeter ratios were calculated for evaluation of cellular morphology. Experiments were carried out in duplicate and the results are reported as the means of three independent assays. Pre-exposure to a red laser protected wild-type and uvrA-deficient E. coli cells against the lethal effect of UVC radiation, and increased the percentage of filamentation and the area-perimeter ratio, depending on UVC fluence and physiological conditions in the cells. Therapeutic, low-level red laser radiation can induce DNA lesions at a sub-lethal level. Consequences to cells and tissues should be considered when clinical protocols based on this laser are carried out.

Low-level laser effects on bacterial cultures submitted to heat stress

“…coli cultures previously exposed to a red laser, but this effect seems more evident in these cultures (figure 2). In fact, data in others studies have demonstrated that laser-induced effects are dependent on the growth phase in E. coli cultures [12,22,23]. These results indicate that, at least in wild type cultures, laserinduced effects on cells submitted to heat stress are dependent on laser wavelength, which is different than the laser-induced effects on cells submitted to hyposmotic [8] and hyperosmotic stress [9].…”

“…However, there are few studies comparing laser-induced effects on biological systems on physiological with non physiological (stressful) conditions [8,9]. Also, genetic characteristics' influence on the effects of these lasers on cells and the participation of DNA repair mechanisms on laser-induced effects has been reported more recently [10][11][12], but this is still controversial, although some data have suggested that these lasers induce sublethal DNA lesions by free radicals generation [13,14].…”

A Comprehensive Review on the Effects of Laser Photobiomodulation on Skeletal Muscle Fatigue in Spastic Patients

“…In addition, it has also been suggested that LLLT may promote changes in the cell's redox state, playing an important role in ion homeostasis and consequently in cellular activity and induce photobiostimulation processes. Besides that, preexposure of PBM has a protective effect against many external agents, such as hydrogen peroxide (H 2 O 2 ) and UV radiation [124,125].…”

Assessing the impact of low level laser therapy (LLLT) on biological systems: a review

“…It was suggested that LLLT might promote changes in the cellular redox state, playing an important role in sustaining cellular activities, and induce photobiostimlative processes [64]. In addition to the above, pre-exposure of PBM had a protective effect against many external agents such as hydrogen peroxide, H 2 O 2 , and UV radiation [65,66]. There is an evolutionary standpoint confirm that NIR pre-exposure protect cells from the hazard impacts of UV exposure, and the re-exposure for NIR radiation could be important for protection maintenance [67,68]…”