Effect of curcumin-mediated photodynamic therapy on methicillin-resistant Staphylococcus aureus and biofilm in vitro

Objective To examine the effect of curcumin-mediated photodynamic therapy (PDT) on Methicillin-resistant Staphylococcus aureus (MRSA) and its biofilm structure. Methods Singlet oxygen sensor green reagent (SOSG) was used to test reactive oxygen species (ROS) generation induced by curcumin-PDT. Both bacterial suspension and MRSA biofilm were divided into 4 groups respectively: Curcumin group, PDT group, Curcumin-PDT group and the Control group. The concentration of curcumin in curcumin group and irradiation group was 1.00, 6.25, 12.50, 25.00 μmol/L. PDT is treated as a 450 nm wavelength light source (irradiance 1 W/cm squared). The survival rates of MRSA planktonic bacteria were calculated with Diluted plate. Survival rates of bacteria within biofilm structure were measured with tetrazolium salt colorimetry (MTT) assay. Microscope was used to observe and identify the changes of the structure of MRSA biofilm. Results The production of ROS induced by curcumin-PDT was increased in a concentration-dependent manner. ROS expression tended to be stable after 5 min within same curcumin concentration. The killing effect of curcumin-PDT on MRSA planktonic bacteria and bacteria inside the biofilm culture was occurred in a concentration-dependent manner, and the survival rate was decreased to (0.38±0.32)% and (34.50±1.44)% respectively with 25 μmol/L curcumin treatment. Meanwhile, scanning electron microscope results showed that the biofilm integrity was disrupted seriously in the curcumin-PDT group. There were no obvious differences between Curcumin group, PDT group and the Control group (t=0.28, 0.71, P>0.05). Conclusion Our study showed that curcumin-PDT not only has a killing effect on MRSA planktonic bacteria and the bacteria inside the biofilm culture in a concentration-dependent manner but also destroy the structure of biofilm. Key words: Curcumin; Photodynamic therapy; Methicillin-resistant staphylococcus aureus; Biofilm