Red and infrared laser therapy inhibits in vitro growth of major bacterial species that commonly colonize skin ulcers.

Low-level laser therapy (LLLT) is used in chronic wounds due to its healing effects. However, bacterial species may colonize these wounds and the optimal parameters for effective bacterial inhibition are not clear. The aim of this study was to analyze the effect of LLLT on bacterial growth in vitro. Bacterial strains including Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa were suspended in saline solution at a concentration of 10(3) cells/ml and exposed to laser irradiation at wavelengths of 660, 830, and 904 nm at fluences of 0 (control), 3, 6, 12, 18, and 24 J/cm(2). An aliquot of the irradiated suspension was spread on the surface of petri plates and incubated at 37 °C for quantification of colony-forming unit after 24, 48, and 72 h. Laser irradiation inhibited the growth of S. aureus at all wavelengths and fluences higher than 12 J/cm(2), showing a strong correlation between increase in fluence and bacterial inhibition. However, for P. aeruginosa, LLLT inhibited growth at all wavelengths only at a fluence of 24 J/cm(2). E. coli had similar growth inhibition at a wavelength of 830 nm at fluences of 3, 6, 12, and 24 J/cm(2). At wavelengths of 660 and 904 nm, growth inhibition was only observed at fluences of 12 and 18 J/cm(2), respectively. LLLT inhibited bacterial growth at all wavelengths, for a maximum of 72 h after irradiation, indicating a correlation between bacterial species, fluence, and wavelength.

Blue Laser Inhibits Bacterial Growth of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa.

OBJECTIVE: The purpose of this study was to analyze the influence of blue laser on bacterial growth of the main species that usually colonize cutaneous ulcers, as well as its effect over time following irradiation. BACKGROUND DATA: The use of blue laser has been described as an adjuvant therapeutic method to inhibit bacterial growth, but there is no consensus about the best parameters to be used. METHODS: Strains of Staphylococcus aureus ATCC 25923, Pseudomonas aeruginosa ATCC 27853, and Escherichia coli ATCC 25922 were suspended in saline solution at a concentration of 1.5×10(3) colony forming units (CFU)/mL. Next, 300 µL of this suspension was transferred to a microtitulation plate and exposed to a single blue laser irradiation (450 nm) at fluences of 0 (control), 3, 6, 12, 18, and 24 J/cm(2). Each suspension was spread over the surface of a Petri plate before being incubated at 37°C, and counts of CFU were determined after 24 and 48 h. RESULTS: Blue laser inhibited the growth of S. aureus and P. aeruginosa at fluences >6 J/cm(2). On the other hand, E. coli was inhibited at all fluences tested, except at 24 J/cm(2). CONCLUSIONS: Blue laser light was capable of inhibiting bacterial growth at low fluences over time, thus presenting no time-dependent effect.