The antimicrobial effect of lethal photosensitization using lasers is well established. Recently, there has been an increasing interest in the replacement of lasers for Light Emission Diode (LEDs) specially in order to decrease the cost of this therapy.
Objectives: The purpose of this study was evaluate the effect of LED associated to toluidine blue O (TBO) on the viability of oral bacteria in different growth phases.
Methods: Suspensions of Streptococcus mutans (Sm), Streptococcus sobrinus (Ss), Streptococcus sanguinis (Sa), S. mutans + S. sobrinus (SmSs), S. mutans + S. sanguinis (SmSa), S. sobrinus + S. sanguinis (SsSa) and S. mutans + S. sobrinus + S. sanguinis (SmSsSa) were grown in brain heart infusion broth in order to establish the exponential, stationary and decline growth phases. Aliquots of each bacterial suspension were exposed to LED (predominant wavelength in 640,8nm - varying between 620-640 nm) using 51,4 J/cm
2 light energy dose in the presence of TBO photosensitizer at 0.1 mg/mL concentration (absorption peak at 632,8 ± 8nm) at the three different growth phases. Controls without exposure to LED/TBO and exposed only to LED or TBO were performed. After irradiation, the suspensions (triplicates) were added to 96 well microtiter plate containing fresh culture medium. The plates had their absorbance measured (660nm) at this moment and 24h later. The bacteria were incubated at 37°C in partial atmosphere of 10% CO
2.
Results: The association of LED/TBO resulted in a total growth inhibition for all microorganisms at three different growth phases. However, significant difference between TBO and LED/TBO treatment was detected only on bacteria submitted to lethal photosensitization at stationary phase.
Conclusion: LED in association to toluidine blue O is effective to kill single and multiple oral bacteria cultures under the mentioned conditions. (Supported by FAPESP #02/00393-8).