title: Effects of 630-, 660-, 810-, and 905-nm laser irradiation delivering radiant exposure of 1-50 J/cm2 on three species of bacteria in vitro.
abstract: OBJECTIVE
  To examine the effects of low-intensity laser therapy (LILT) on bacterial growth in vitro.
  
  
  BACKGROUND
  LILT is undergoing investigation as a treatment for accelerating healing of open wounds. The potential of coincident effects on wound bacteria has received little attention. Increased bacterial proliferation could further delay recovery; conversely inhibition could be beneficial.
  
  
  METHODS
  Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus were plated on agar and then irradiated with wavelengths of 630, 660, 810, and 905 nm (0.015 W/cm(2)) and radiant exposures of 1-50 J/cm(2). In addition, E. coli was irradiated with 810 nm at an irradiance of 0.03 W/cm(2) (1-50 J/cm(2)). Cells were counted after 20 h of incubation post LILT. Repeated measures ANOVA and Tukey adjusted post hoc tests were used for analysis.
  
  
  RESULTS
  There were interactions between wavelength and species (p = 0.0001) and between wavelength and radiant exposure (p = 0.007) in the overall effects on bacterial growth; therefore, individual wavelengths were analyzed. Over all types of bacteria, there were overall growth effects using 810- and 630-nm lasers, with species differences at 630 nm. Effects occurred at low radiant exposures (1-20 J/cm(2)). Overall effects were marginal using 660 nm and negative at 905 nm. Inhibition of P. aeruginosa followed irradiation using 810 nm at 5 J/cm(2) (-23%; p = 0.02). Irradiation using 630 nm at 1 J/cm(2) inhibited P. aeruginosa and E. coli (-27%). Irradiation using 810 nm (0.015 W/cm(2)) increased E. coli growth, but with increased irradiance (0.03 W/cm(2)) the growth was significant (p = 0.04), reaching 30% at 20 J/cm(2) (p = 0.01). S. aureus growth increased 27% following 905-nm irradiation at 50 J/cm(2).
  
  
  CONCLUSIONS
  LILT applied to wounds, delivering commonly used wavelengths and radiant exposures in the range of 1-20 J/cm(2), could produce changes in bacterial growth of considerable importance for wound healing. A wavelength of 630 nm appeared to be most commonly associated with bacterial inhibition. The findings of this study might be useful as a basis for selecting LILT for infected wounds.
authors.affiliation: Rehabilitation Services, Mount Sinai Hospital and Department of Physical Therapy, University of Toronto, Toronto, Ontario, Canada. e.nussbaum@utoronto.ca
authors.forename: Ethne L
authors.initials: EL
authors.lastname: Nussbaum
authors.forename: Lothar
authors.initials: L
authors.lastname: Lilge
authors.forename: Tony
authors.initials: T
authors.lastname: Mazzulli
mesh_terms: D004926:Escherichia coli / Q000528:radiation effects*; D028022:Low-Level Light Therapy / Q000379:methods*; D011550:Pseudomonas aeruginosa / Q000528:radiation effects*; D013211:Staphylococcus aureus / Q000528:radiation effects*; D014945:Wound Healing / Q000528:radiation effects; D014946:Wound Infection / Q000532:radiotherapy