The biofilms were grown on sample pieces of acrylic resin and subjected to photodynamic therapy using a 660-nm diode laser and photosensitizer concentrations ranging from 37.5 to 3000 ¦ÌM. After photodynamic therapy, cells from the biofilms were dispersed in a homogenizer and cultured in Brain Heart Infusion broth for quantification of colony-forming units per experimental protocol. For each tested microorganism, two control groups were maintained: one exposed to the laser radiation without the photosensitizer (L+PS? and other treated with the photosensitizer without exposure to the red laser light (L?PS+). The results were subjected to descriptive statistical analysis.
The best results for S. aureus and E. coli biofilms were obtained with photosensitizer concentrations of approximately 300 ¦ÌM methylene blue, with microbial reductions of 0.8-1.0 log10; 150 ¦ÌM toluidine blue, with microbial reductions of 0.9-1.0 log10; and 3000 ¦ÌM malachite green, with microbial reductions of 1.6-4.0 log10.
Greater microbial reduction was achieved with the malachite green photosensitizer when used at higher concentrations than those employed for the phenothiazinic dyes.