Inhibition of Mycobacterium smegmatis using near-IR and blue light.

Background: Objective of current study is to determine whether near-IR, alone or combined with blue light and delivered at a low rate, could lower the dose needed to effectively inhibit Mycobacterium smegmatis in vitro. We have studied the effect of blue light on M. smegmatis and found that a bactericidal outcome can be obtained with high doses of blue light. Methods: The organism was treated in vitro with 464, 850 and combined 464 & 850nm light emitted from a supraluminous diode (SLD) array. Doses of 30, 45 and 60 J/cm2 were used. Colony counts were performed and compared to untreated controls using Student t tests, a two-way Repeated Measures ANOVA and a one-way ANOVA with Tukey post hoc analysis. Results: Statistically significant inhibition was observed for each individual wavelength and dose combination (p < 0.05). Two-way ANOVA demonstrated an interaction effect between wavelength and dose (F1, 9 = 358.585; p - 0.000). Post hoc analysis using one-way ANOVA (F2, 27 = 11.211; p = 0.00) and Tukey’s HSD identified 850nm at 45 J/cm2 to be the most effective wavelength / dose combination. Conclusions: 850nm irradiation delivered at 45 J/cm2 is a wavelength /dose combination that can be expected to produce a significant inhibition of M. smegmatis in vitro.

Combined 624-nm and 850-nm illumination at low rates leads to enhanced inhibition of Candida albicans.

Background: To determine whether combinations of red and infrared light could improve inhibition of Candida albicans and whether combining wavelengths and altering rate of energy delivery could prevent the formation of resistance to light energy. Methods: C. albicans was tested because of the common appearance in human skin and mucous membrane infections. The organism was treated in vitro with a combination of 624-nm (red) and 850-nm (infrared) light emitted from a supraluminous diode (SLD) array. Doses of 9, and 30 J/cm2 were used. Rate of energy delivery was also manipulated. Colony counts were performed and compared to untreated controls using Student t tests and one-way ANOVA with Tukey post hoc analysis. Results: The combination of 624 and 850-nm light energy at 30 J/cm2 was an effective (p ≤ 0.05) inhibitor of C. albicans across all seven stages of the experiment. The combination of 624 and 850-nm wavelengths produced a maximum kill rate [{control – treated / control} X 100] of 76.24% and an average kill rate of 54% across the seven stages of the experiment. Conclusions: A Combination of 624-nm and 850-nm light from an SLD array can inhibit the growth of C. albicans in vitro. Altering delivery rate of the energy can delay resistance formation in this organism.