Publication:

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.