Effects of low-level laser therapy (LLLT) of 810 nm upon in vitro growth of bacteria: relevance of irradiance and radiant exposure.
OBJECTIVE
The aim of this study was to investigate the irradiance-dependency of low-level laser therapy (LLLT) effects on bacterial growth.


BACKGROUND
LLLT is applied to open wounds to improve healing; however, its effect on wound bacteria is not well understood.


METHODS
Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus were irradiated using a wavelength of 810 nm at irradiances of 0.015 W/cm2 (0-50 J/cm2) and 0.03 W/cm2 (0-80 J/cm2). Bacteria were counted after 20 h of incubation.


RESULTS
LLLT effects varied significantly with species. P.aeruginosa growth decreased overall dependent on an interaction of irradiance and radiant exposure; greatest inhibition was produced using high irradiance delivering radiant exposures in the range of 1-20 J/cm2 (p = 0.001-0.04). In contrast, E. coli growth increased overall (p = 0.01), regardless of irradiance; greatest effects were produced using low radiant exposures (1-20 J/cm2). There was a main effect for irradiance (p = 0.03) on S. aureus growth; however, growth was not different compared with controls. Additional analysis showed that there were differences in growth of P.aeruginosa when comparing samples that were matched by exposure times (66, 329, 658, 1316, 1974, and 2632 sec) rather than radiant exposure; this suggests that irradiance rather than exposure time was the significant factor in P. aeruginosa inhibition.


CONCLUSIONS
These findings have immediate relevancy in the use of LLLT for infected wounds. Exposure to 810-nm irradiation (0.03 W/cm2) could potentially benefit wounds infected with P. aeruginosa. However, increased E. coli growth could further delay recovery.
Nussbaum
Ethne L
EL
Rehabilitation Services, Mount Sinai Hospital and Department of Physical Therapy, University of Toronto, Toronto, Ontario, Canada. e.nussbaum@utoronto.ca
Lilge
Lothar
L
Mazzulli
Tony
T
D001419:Bacteria / Q000254:growth & development* / Q000528:radiation effects; D018407:Bacterial Physiological Phenomena / Q000528:radiation effects*; D002460:Cell Line; D004926:Escherichia coli / Q000254:growth & development / Q000528:radiation effects; D028022:Low-Level Light Therapy / Q000379:methods*; D011550:Pseudomonas aeruginosa / Q000254:growth & development / Q000528:radiation effects; D013211:Staphylococcus aureus / Q000254:growth & development / Q000528:radiation effects