Effects of low intensity laser irradiation during healing of skin lesions in the rat

Abstract

This study demonstrates that while clearing wounds of certain bacteria is feasible it does not necessarily translate into a healing advantage. When normal flora are disturbed, environmental organisms more readily colonize the wound surface. It is not clear when using 808 nm light whether the loss of normal flora in the wound alone is responsible for the proliferation of S. aureus or whether the light adds to the effect by stimulating S. aureus growth.

Effects of low intensity laser irradiation during healing of infected skin wounds in the rat

“…Dependent on radiant exposure, growth may be increased or decreased; clearing wounds of bacteria is possible using some combinations of wavelength and radiant exposure. In our laboratory, wounds in the rat were cleared of bacteria using red light at radiant exposure of 20 J/cm 2 ; importantly, these sterile wounds healed more slowly than control wounds [22]. We found that 635-nm light at radiant exposure of 1 J/cm 2 produced the most beneficial effects on wound healing, interestingly, without disturbing the normal wound bioburden [22].…”

“…Day 8 was selected because the early inflammatory processes should have resolved by this time. Day 19 was selected in order to conclude the study at a standardized time for all animals and when above 70% wound closure could be expected; this was based on pilot work and a previous study [22].…”

“…Red light was selected because in previous work we found that red light at low radiant exposure improved healing during the inflammatory phase of wound repair and that at higher radiant-exposure red light had a bactericidal effect [22]. Selection of 808-nm light was also based on previous work demonstrating that 808-nm light produced undesirable proliferation of S. aureus [22].…”

“…Sections were graded for wound healing according to seven parameters related to acute inflammatory response and repair: edema, polymorphonuclear leucocytes, macrophages, granulation tissue, fibroblasts, collagen deposition, and evidence of epithelialization. Each feature was semi quantitatively evaluated (from 0=absent, to 3=prominent) based on well defined and reproducible histological parameter classification reported by us previously [16,22].…”

“…In our laboratory, wounds in the rat were cleared of bacteria using red light at radiant exposure of 20 J/cm 2 ; importantly, these sterile wounds healed more slowly than control wounds [22]. We found that 635-nm light at radiant exposure of 1 J/cm 2 produced the most beneficial effects on wound healing, interestingly, without disturbing the normal wound bioburden [22]. The major difference between the prior study and the work reported here is that previously the wounds were exposed to opportunistic environmental organisms whereas in this study wounds were infected using a standardized bacterial inoculum.…”