Delaying the Onset of Resistance Formation: Effect of Manipulating Dose, Wavelength, and Rate of Energy Delivery of 405-, 464-, and 850-Nanometer Light for Staphylococcus aureus

To determine whether manipulation of dose, wavelength, and rate of energy delivery could delay the onset of previously demonstrated Staphylococcus aureus resistance to blue light. The organism was treated in vitro with 405 nm, 464 nm, and combined 464 nm and with 850 nm light emitted from a supraluminous diode (SLD) array. Doses of 9 J/cm2 and 30 J/cm2 were used. Rates of energy delivery were also varied from 10 mW/cm2 to 125 mW/cm2. Seven stages were employed to test for resistance formation. Colony counts were performed and compared to untreated controls using Student t tests and one-way ANOVA with Tukey post hoc analysis. A best dose, wavelength, and rate of delivery combination was determined at each stage and it did produce a significant kill rate (P ≤ 0.05) at each stage. Analysis of variance demonstrated that no loss of effectiveness (formation of resistance) occurred over the 7 stages. Appropriate combinations of dose, wavelength, and rate of energy delivery can delay resistance formation to light as a bactericidal agent for S. aureus. .