Inactivation of mycobacterium smegmatis following exposure to 405-nanometer light from a supraluminous diode array.

Objective: To determine the potential for blue light (405 nm) to produce a bactericidal effect on Mycobacterium smegmatis. Additionally, the study sought to evaluate a series of doses in terms of their respective bactericidal capabilities.

Background Data: The effect of blue light on Staphylococcus aureus has been studied and it was found that a bactericidal outcome can be obtained with low doses of blue light.

Methods: M. smegmatis was tested because of the recent appearance of the Mycobacterium family of organisms as a public health threat among persons receiving tattoos. The organism was treated in vitro with 405 nm light emitted from a supraluminous diode (SLD) array. Doses of 60 Jcm-2, 90 Jcm-2, 120 Jcm-2, 150 Jcm-2, 180 Jcm-2, 215 Jcm-2, and 250 Jcm-2 were used. Colony counts were performed and compared to untreated controls using Student t tests and one-way ANOVA with Tukey post hoc analysis.

Results: The results revealed statistically significant bactericidal effects of the blue light on M. smegmatis (F6, 28 = 50.518, P = 0.000). The treatment reduced the number of bacterial colonies at all doses, but 60 Jcm-2 did not produce a statistically significant kill rate. All other doses produced a significant kill rate with 120 Jcm-2, 150 Jcm-2, and 215 Jcm-2, demonstrating the most effective kill rates of 98.3%, 96.7%, and 100%, respectively.

Conclusions: Appropriate doses of 405 nm light from an SLD array can kill M. smegmatis in vitro. A dose of at least 100 Jcm-2 dose is needed for the most effective inactivation of the organism. The dose response for this organism to blue light is not linear. Some degree of effectiveness is lost at 180 Jcm-2 and 250 Jcm-2. .