Sonophotodynamic Therapy for the inactivation of Staphylococcus aureus biofilm

Antimicrobial Photodynamic Therapy (aPDT) has been investigated as an alternative method for the inactivation of microorganisms. This treatment, which is based on the application of a photosensitizer and visible light, has a reduced effectiveness when the microorganisms are organized as biofilm. Recently, Sonodynamic Therapy (SDT) has also been suggested as an antimicrobial treatment presenting the advantage of activating photosensitizer by the use of ultrasound (US), which propagates deeper into the tissue and is able to disrupt the biofilm. In this sense, this study aimed to evaluate the efficacy of associating US with aPDT mediated by curcumin (Cur), in order to disrupt Staphylococcus aureus biofilms and increase the inactivation of the bacteria. For this, standardized suspensions of S. aureus were prepared (108) and after 48 h of biofilm formation, samples received the following treatments: aPDT (Cur and blue LED light), SDT (Cur and US) and SPDT (incubation with Cur and, then, simultaneously application of US and light). Additional samples received Cur, light or US only, or no treatment (control). To determine cell survival, the biofilms were removed and aliquots were serially diluted and plated in Brain Heart Infusion Agar. After 24 h of incubation at 37°C, the colony forming units were calculated. The preliminary results demonstrated that US in combination with aPDT (SPDT) showed higher and significant bacteria reduction compared to the application of SDT and aPDT. Cur, LED light or US alone did not have any effect. This result highlights the enhanced effect of ultrasound and aPDT against S. aureus biofilms.