In this study, we evaluated the effectiveness of ALA-PDT on biofilms formed by methicillin-resistant Staphylococcus aureus (ATCC 43300) and methicillin-resistant S epidermidis (MRSE 287). The strains were cultured with 40 mM of ALA in 24-well microtiter plates containing coverslips at 37¡ãC for 24 h in the dark. PpIX fluorescence in biofilms formed by the two strains was observed by confocal laser scanning microscopy (CLSM). ALA-treated biofilms were irradiated at different doses (0, 100, 200, and 300 J/cm2) using a semiconductor laser. Biofilm exposed only to Tryptone Soy Broth or irradiation (300 J/cm2) was investigated. Viability determination, CLSM, and scanning electron microscopy were used to investigate the photodynamic inactivation of ALA-PDT.
ALA was absorbed and converted to PpIX by both methicillin-resistant S aureus and methicillin-resistant S epidermidis. No cell inactivation was detectable in biofilms of either strain incubated with ALA without exposure to light, incubated with Tryptone Soy Broth only, or irradiated with red light only. However, a significant number of cells within biofilms were inactivated during irradiation with different doses of red light in the presence of 40 mM of ALA in a dose-dependent manner. The drastic reduction in cell survival within biofilms and the disruption of biofilms were confirmed by CLSM and scanning electron microscopy.
ALA-PDT has the potential to eliminate the biofilm of Staphylococcus, especially antibiotic-resistant strains, effectively. It will be suitable for the treatment of superficial local infections such as surface wounds, burns, oral and dental infections, dermatologic infections such as acne and rosacea, and soft tissue and bone infections with bone exposure.